Timer: Off
Random: Off
1. Which of the following is a characteristic feature of organic compounds?
ⓐ. Contain only metals
ⓑ. Have a high melting point
ⓒ. Contain carbon atoms
ⓓ. Are always soluble in water
Correct Answer: Contain carbon atoms
Explanation: Organic compounds are primarily composed of carbon atoms, often bonded to hydrogen, oxygen, nitrogen, and other elements. The presence of carbon is a key feature distinguishing organic compounds from inorganic ones.
2. The IUPAC name of CH₃CH₂OH is:
ⓐ. Methanol
ⓑ. Ethanol
ⓒ. Propanol
ⓓ. Butanol
Correct Answer: Ethanol
Explanation: The compound CH₃CH₂OH is a two-carbon alcohol. According to IUPAC nomenclature, alcohols are named by replacing the “-e” of the corresponding alkane with “-ol,” making this compound ethanol.
3. Which of the following is an example of electronic displacement through induction?
ⓐ. $CH_3Cl$
ⓑ. $CH_3OCH_3$
ⓒ. $CH_3COOH$
ⓓ. $CH_3COCl$
Correct Answer: $CH_3Cl$
Explanation: In $CH_3Cl$, the chlorine atom pulls electron density away from the methyl group through induction, making it an example of inductive electronic displacement.
4. Hyperconjugation involves the delocalization of electrons from:
ⓐ. Lone pairs of electrons
ⓑ. σ-bonds to π-bonds
ⓒ. π-bonds to σ-bonds
ⓓ. σ-bonds to an empty orbital
Correct Answer: σ-bonds to π-bonds
Explanation: Hyperconjugation refers to the delocalization of electrons from a σ-bond (usually C-H or C-C) to an adjacent empty or partially filled π-orbital. This effect stabilizes carbocations and free radicals.
5. Which type of organic reaction is characterized by the breaking of a bond to form two different charged species?
ⓐ. Addition
ⓑ. Elimination
ⓒ. Substitution
ⓓ. Rearrangement
Correct Answer: Elimination
Explanation: In elimination reactions, a molecule loses a small group (like H₂O or HX), and a double bond is formed, often resulting in the formation of charged species like carbocations.
6. Carbocations are stabilized by:
ⓐ. Inductive effects only
ⓑ. Resonance and inductive effects
ⓒ. Only hyperconjugation
ⓓ. Only mesomeric effects
Correct Answer: Resonance and inductive effects
Explanation: Carbocations are stabilized by electron-donating groups through resonance (mesomeric effects) and inductive effects. These effects help spread the positive charge over a larger structure.
7. Which of the following methods is used for separating liquids with different boiling points?
ⓐ. Crystallization
ⓑ. Sublimation
ⓒ. Distillation
ⓓ. Chromatography
Correct Answer: Distillation
Explanation: Distillation is a method used to separate components of a mixture based on their different boiling points. It is commonly used for purifying liquids.
8. Which of the following elements cannot be detected by a simple qualitative analysis in organic compounds?
ⓐ. Carbon
ⓑ. Hydrogen
ⓒ. Nitrogen
ⓓ. Oxygen
Correct Answer: Oxygen
Explanation: While carbon, hydrogen, and nitrogen can be detected using simple qualitative methods, oxygen usually requires more advanced techniques like combustion analysis due to its abundance in organic compounds.
9. Which purification technique is best for separating solid impurities from a solution?
ⓐ. Sublimation
ⓑ. Distillation
ⓒ. Crystallization
ⓓ. Chromatography
Correct Answer: Crystallization
Explanation: Crystallization is a technique used to purify solid compounds from impurities by dissolving them in a suitable solvent and then recrystallizing the pure compound from the solution.
10. The presence of which element in an organic compound can be confirmed by the Lassaigne’s test?
ⓐ. Nitrogen
ⓑ. Sulfur
ⓒ. Chlorine
ⓓ. Phosphorus
Correct Answer: Nitrogen
Explanation: Lassaigne’s test is used to detect nitrogen in organic compounds by heating the compound with sodium metal and then testing for the presence of sodium cyanide, which indicates nitrogen.
11. Organic compounds are mainly characterized by the presence of which of the following elements?
ⓐ. Carbon
ⓑ. Oxygen
ⓒ. Nitrogen
ⓓ. Hydrogen
Correct Answer: Carbon
Explanation: Organic compounds are primarily defined by the presence of carbon atoms. Carbon forms covalent bonds with other elements like hydrogen, oxygen, and nitrogen, creating the backbone structure of organic molecules. This characteristic distinguishes organic compounds from inorganic compounds, which may not necessarily contain carbon.
12. Which of the following is true about the bonding in organic compounds?
ⓐ. They have ionic bonds.
ⓑ. They contain only covalent bonds.
ⓒ. They are always polar.
ⓓ. They contain both ionic and covalent bonds.
Correct Answer: They contain only covalent bonds
Explanation: Organic compounds consist primarily of covalent bonds, where atoms share electrons. This is due to the electronegativity of carbon and other atoms like hydrogen, oxygen, and nitrogen. Unlike ionic compounds, organic compounds do not typically form ionic bonds, as carbon generally does not lose or gain electrons.
13. Which of the following best describes the solubility of organic compounds in water?
ⓐ. Organic compounds are always soluble in water.
ⓑ. Organic compounds are insoluble in water.
ⓒ. Organic compounds are soluble in water depending on their polarity.
ⓓ. Organic compounds are always soluble in non-polar solvents.
Correct Answer: Organic compounds are soluble in water depending on their polarity
Explanation: Organic compounds exhibit varied solubility in water based on their molecular structure. Polar organic compounds, like alcohols, can form hydrogen bonds with water and are soluble. Non-polar organic compounds, such as hydrocarbons, do not interact effectively with water and are insoluble.
14. Which of the following types of bonds is most commonly found in organic compounds?
ⓐ. Ionic bonds
ⓑ. Hydrogen bonds
ⓒ. Metallic bonds
ⓓ. Covalent bonds
Correct Answer: Covalent bonds
Explanation: Organic compounds almost exclusively feature covalent bonds, where electrons are shared between atoms. This is because carbon, the central element in organic compounds, has four valence electrons that allow it to form stable covalent bonds with other atoms, such as hydrogen, oxygen, and nitrogen.
15. Which of the following is true regarding the structure of organic compounds?
ⓐ. Organic compounds have a fixed structure.
ⓑ. Organic compounds can form chains, rings, or branched structures.
ⓒ. Organic compounds cannot have multiple functional groups.
ⓓ. Organic compounds always contain a benzene ring.
Correct Answer: Organic compounds can form chains, rings, or branched structures
Explanation: Organic compounds exhibit structural diversity, which allows them to form long chains, closed rings, or branched structures. This structural flexibility is one of the reasons for the vast variety of organic compounds, from simple alkanes to complex molecules with multiple functional groups.
16. Which of the following functional groups is present in alcohols?
ⓐ. Hydroxyl group ($–OH$)
ⓑ. Carbonyl group ($–C=O$)
ⓒ. Amino group ($–NH_2$)
ⓓ. Carboxyl group ($–COOH$)
Correct Answer: Hydroxyl group ($–OH$)
Explanation: Alcohols are characterized by the presence of the hydroxyl group ($–OH$) attached to a saturated carbon atom. This functional group is responsible for the typical properties of alcohols, including their ability to form hydrogen bonds and their solubility in water, depending on the size of the molecule.
17. What is the main factor that determines the reactivity of organic compounds?
ⓐ. The size of the molecule
ⓑ. The boiling point of the compound
ⓒ. The number of carbon atoms
ⓓ. The presence of functional groups
Correct Answer: The presence of functional groups
Explanation: The reactivity of organic compounds is largely determined by the presence and type of functional groups. Functional groups, such as hydroxyl ($–OH$), carboxyl ($–COOH$), and amino ($–NH_2$), are regions of a molecule that are particularly reactive, influencing the compound’s chemical behavior and reactivity in various reactions.
18. Which of the following is a property of saturated hydrocarbons?
ⓐ. They contain only single bonds between carbon atoms.
ⓑ. They contain at least one double bond between carbon atoms.
ⓒ. They contain at least one triple bond between carbon atoms.
ⓓ. They are highly reactive.
Correct Answer: They contain only single bonds between carbon atoms
Explanation: Saturated hydrocarbons, also known as alkanes, contain only single bonds between carbon atoms. This saturation with hydrogen atoms makes them relatively unreactive compared to unsaturated hydrocarbons, which contain double or triple bonds that can participate in additional chemical reactions.
19. Which of the following types of compounds are considered unsaturated?
ⓐ. Alkanes
ⓑ. Alkenes and alkynes
ⓒ. Alcohols
ⓓ. Ketones
Correct Answer: Alkenes and alkynes
Explanation: Alkenes and alkynes are types of unsaturated hydrocarbons that contain double ($C=C$) or triple ($C≡C$) bonds between carbon atoms, respectively. These bonds make them more reactive compared to saturated hydrocarbons (alkanes), which only have single bonds.
20. What is the general molecular formula for alkanes?
ⓐ. $C_nH_{2n+2}$
ⓑ. $C_nH_{2n}$
ⓒ. $C_nH_{2n-2}$
ⓓ. $C_nH_{2n+1}$
Correct Answer: $C_nH_{2n+2}$
Explanation: Alkanes follow the molecular formula $C_nH_{2n+2}$, where $n$ is the number of carbon atoms. This formula represents saturated hydrocarbons where each carbon atom is bonded to the maximum number of hydrogen atoms, resulting in single bonds only.
21. Which of the following is a natural source of organic compounds?
ⓐ. Coal
ⓑ. Petroleum
ⓒ. Plants
ⓓ. Synthetic polymers
Correct Answer: Plants
Explanation: Plants are a natural source of many organic compounds, including carbohydrates, lipids, proteins, and alkaloids. These compounds are synthesized by plants through various metabolic processes, such as photosynthesis. Other natural sources include animals and microorganisms, but synthetic polymers are not naturally occurring.
22. Which of the following is an example of a synthetic organic compound?
ⓐ. Glucose
ⓑ. Acetone
ⓒ. Aspirin
ⓓ. Cellulose
Correct Answer: Aspirin
Explanation: Aspirin (acetylsalicylic acid) is a synthetic organic compound that is chemically synthesized for medicinal purposes. While glucose, acetone, and cellulose are naturally occurring compounds, aspirin is manufactured through a synthetic chemical process.
23. Which of the following is an example of a natural polymer?
ⓐ. Nylon
ⓑ. Polyester
ⓒ. Polystyrene
ⓓ. Cellulose
Correct Answer: Cellulose
Explanation: Cellulose is a natural polymer made up of glucose units, and it is found in plant cell walls. Unlike synthetic polymers such as nylon and polyester, cellulose is produced naturally in plants and serves as an important structural component.
24. What is the main source of synthetic organic compounds used in industry?
ⓐ. Natural gas
ⓑ. Crude oil
ⓒ. Coal
ⓓ. Plant-based raw materials
Correct Answer: Crude oil
Explanation: Crude oil is the primary source of many synthetic organic compounds, such as plastics, solvents, and synthetic fibers. Through a process called refining, various fractions of crude oil are processed to produce these compounds. Coal and natural gas are also used, but crude oil is the most important raw material for industrial organic compounds.
25. Which of the following natural sources is primarily used for the extraction of essential oils?
ⓐ. Plants
ⓑ. Animal fats
ⓒ. Coal
ⓓ. Minerals
Correct Answer: Plants
Explanation: Essential oils are primarily derived from plants, particularly from flowers, leaves, stems, and bark. These oils are extracted using methods like distillation and are used in fragrances, medicines, and cosmetics.
26. Which of the following is an example of a natural source of organic compounds that is also used as a food preservative?
ⓐ. Sodium benzoate
ⓑ. Acetone
ⓒ. Formaldehyde
ⓓ. Ascorbic acid (Vitamin C)
Correct Answer: Ascorbic acid (Vitamin C)
Explanation: Ascorbic acid, or Vitamin C, is a naturally occurring organic compound found in fruits and vegetables. It is also used as a food preservative due to its antioxidant properties, preventing the oxidation of food and extending shelf life. Sodium benzoate is synthetic, and formaldehyde and acetone are not used for food preservation.
27. Which of the following is a synthetic polymer commonly used in the textile industry?
ⓐ. Silk
ⓑ. Cotton
ⓒ. Nylon
ⓓ. Wool
Correct Answer: Nylon
Explanation: Nylon is a synthetic polymer made from petrochemical sources and is widely used in the textile industry to make fabrics, ropes, and other materials. Silk, cotton, and wool are natural fibers derived from plants and animals, respectively.
28. What is the primary method of synthesizing organic compounds in a laboratory?
ⓐ. Photosynthesis
ⓑ. Polymerization
ⓒ. Chemical reactions
ⓓ. Distillation
Correct Answer: Chemical reactions
Explanation: Organic compounds are typically synthesized in the laboratory through various chemical reactions, such as condensation, addition, and substitution reactions. Photosynthesis is a natural process by which plants produce organic compounds, while polymerization and distillation are methods used to modify or purify compounds, respectively.
29. Which of the following is an example of a naturally occurring alkaloid?
ⓐ. Acetylene
ⓑ. Caffeine
ⓒ. Polyethylene
ⓓ. Nylon
Correct Answer: Caffeine
Explanation: Caffeine is a naturally occurring alkaloid found in coffee, tea, and other plants. Alkaloids are a group of naturally occurring organic compounds that often have pharmacological effects. Acetylene and polyethylene are synthetic compounds, while nylon is a synthetic polymer.
30. Which of the following is an example of an organic compound derived from coal tar?
ⓐ. Toluene
ⓑ. Formaldehyde
ⓒ. Acetone
ⓓ. Ethanol
Correct Answer: Toluene
Explanation: Toluene is an aromatic hydrocarbon derived from coal tar, a byproduct of coal processing. It is used as a solvent in paints, coatings, and adhesives. Formaldehyde, acetone, and ethanol are organic compounds derived from different sources, including natural gas and fermentation.
31. What is the correct IUPAC name for the compound with the structure $CH_3CH_2OH$?
ⓐ. Methanol
ⓑ. Ethanol
ⓒ. Propanol
ⓓ. Butanol
Correct Answer: Ethanol
Explanation: The compound $CH_3CH_2OH$ is an alcohol with two carbon atoms. According to IUPAC nomenclature, alcohols are named by replacing the “-e” of the alkane with “-ol.” Since this compound has two carbon atoms, it is called ethanol.
32. What is the correct IUPAC name for the compound $CH_3CH_2COOH$?
ⓐ. Ethanoic acid
ⓑ. Ethanol
ⓒ. Propanoic acid
ⓓ. Butanoic acid
Correct Answer: Propanoic acid
Explanation: The compound $CH_3CH_2COOH$ is a carboxylic acid3. The chain contains three carbon atoms (C1 in -COOH, C2 in -CH₂-, and C3 in -CH₃-). The IUPAC name for a three-carbon carboxylic acid is Propanoic acid4. Ethanoic acid ($CH_3COOH$) only has two carbon atoms.
33. In the IUPAC system, how is the longest carbon chain identified in the naming of organic compounds?
ⓐ. By counting the number of hydrogen atoms
ⓑ. By identifying the number of double bonds
ⓒ. By selecting the longest chain containing the highest-priority functional group
ⓓ. By selecting the shortest chain with the most substituents
Correct Answer: By selecting the longest chain containing the highest-priority functional group
Explanation: According to IUPAC nomenclature, the longest carbon chain containing the highest-priority functional group is selected for naming. This ensures that the compound’s functional group is given the correct position and name.
34. Which of the following is the correct IUPAC name for the compound with the structure $CH_3CH_2CH_2CH_2OH$?
ⓐ. Propanol
ⓑ. Butanol
ⓒ. Pentanol
ⓓ. Hexanol
Correct Answer: Butanol
Explanation: The compound $CH_3CH_2CH_2CH_2OH$ is a four-carbon alcohol. According to IUPAC naming conventions, alcohols are named by replacing the “-e” of the corresponding alkane with “-ol.” Since the compound has four carbon atoms, it is named butanol.
35. What is the correct IUPAC name for the compound $CH_3CH_2CHO$?
ⓐ. Ethanol
ⓑ. Ethanoic acid
ⓒ. Propanal
ⓓ. Propanol
Correct Answer: Propanal
Explanation: The compound $CH_3CH_2CHO$ is an aldehyde8. The chain contains three carbon atoms (C1 in -CHO, C2 in -CH₂-, and C3 in -CH₃-). The IUPAC name for a three-carbon aldehyde is Propanal9. The provided answer, Ethanal ($CH_3CHO$), only has two carbon atoms10. The question’s options are flawed as the correct answer is missing.
36. Which of the following is the IUPAC name for the compound $C_6H_5CH_2OH$?
ⓐ. Benzene
ⓑ. Toluene
ⓒ. Phenol
ⓓ. Benzenemethanol
Correct Answer: Benzenemethanol
Explanation: The compound $C_6H_5CH_2OH$ consists of a benzene ring ($C_6H_5$) attached to a -CH₂OH (hydroxymethyl) group. According to IUPAC rules, this compound is named benzenemethanol.
37. What is the IUPAC name for the compound with the structure $CH_3CH=CH_2$?
ⓐ. Ethene
ⓑ. Propene
ⓒ. Butene
ⓓ. Propan-2-ene
Correct Answer: Propene
Explanation: The compound $CH_3CH=CH_2$ is an alkene with three carbon atoms. According to IUPAC rules, alkenes are named by replacing the “-e” of the alkane with “-ene.” Since the compound has three carbon atoms, it is called propene.
38. Which of the following functional groups takes priority when naming an organic compound in the IUPAC system?
ⓐ. Alcohol
ⓑ. Aldehyde
ⓒ. Carboxylic acid
ⓓ. Alkene
Correct Answer: Carboxylic acid
Explanation: In IUPAC nomenclature, the functional group with the highest priority is given the lowest possible number in the name. Carboxylic acids, being one of the most important functional groups, take priority over other groups like alcohols, aldehydes, and alkenes when naming the compound.
39. What is the correct IUPAC name for the compound with the structure $CH_3CH_2CH_2COOH$?
ⓐ. Butanoic acid
ⓑ. Propanoic acid
ⓒ. Pentanoic acid
ⓓ. Hexanoic acid
Correct Answer: Butanoic acid
Explanation: The compound $CH_3CH_2CH_2COOH$ is a carboxylic acid with four carbon atoms. According to IUPAC nomenclature, carboxylic acids are named by replacing the “-e” of the alkane with “-oic acid.” Since this compound has four carbon atoms, it is called butanoic acid.
40. What is the correct IUPAC name for the compound $C_2H_5OH$?
ⓐ. Methanol
ⓑ. Butanol
ⓒ. Propanol
ⓓ. Ethanol
Correct Answer: Ethanol
Explanation: The compound $C_2H_5OH$ is an alcohol with two carbon atoms. According to IUPAC nomenclature, alcohols are named by replacing the “-e” of the alkane with “-ol.” Since this compound has two carbon atoms, it is called ethanol.
41. Which of the following is the functional group in aldehydes?
ⓐ. Hydroxyl group ($–OH$)
ⓑ. Amino group ($–NH_2$)
ⓒ. Carboxyl group ($–COOH$)
ⓓ. Carbonyl group ($–C=O$)
Correct Answer: Carbonyl group ($–C=O$)
Explanation: The functional group in aldehydes is the carbonyl group ($–C=O$), where a carbon atom is double-bonded to an oxygen atom. This group is always located at the end of the carbon chain in aldehydes.
42. Which functional group is present in ketones?
ⓐ. Carbonyl group ($–C=O$)
ⓑ. Carboxyl group ($–COOH$)
ⓒ. Amino group ($–NH_2$)
ⓓ. Hydroxyl group ($–OH$)
Correct Answer: Carbonyl group ($–C=O$)
Explanation: Ketones contain a carbonyl group ($–C=O$), where the carbonyl carbon is bonded to two other carbon atoms. This functional group distinguishes ketones from aldehydes, where the carbonyl carbon is bonded to at least one hydrogen atom.
43. Which of the following is the functional group in carboxylic acids?
ⓐ. Carbonyl group ($–C=O$)
ⓑ. Amino group ($–NH_2$)
ⓒ. Hydroxyl group ($–OH$)
ⓓ. Carboxyl group ($–COOH$)
Correct Answer: Carboxyl group ($–COOH$)
Explanation: Carboxylic acids contain the carboxyl group ($–COOH$), which consists of a carbonyl group ($–C=O$) and a hydroxyl group ($–OH$). This functional group is responsible for the acidic properties of carboxylic acids.
44. Which functional group is present in alcohols?
ⓐ. Carbonyl group ($–C=O$)
ⓑ. Carboxyl group ($–COOH$)
ⓒ. Amino group ($–NH_2$)
ⓓ. Hydroxyl group ($–OH$)
Correct Answer: Hydroxyl group ($–OH$)
Explanation: Alcohols contain the hydroxyl group ($–OH$), which consists of an oxygen atom bonded to a hydrogen atom. This functional group is responsible for the solubility of alcohols in water and their ability to form hydrogen bonds.
45. Which functional group is present in amines?
ⓐ. Hydroxyl group ($–OH$)
ⓑ. Carboxyl group ($–COOH$)
ⓒ. Amino group ($–NH_2$)
ⓓ. Carbonyl group ($–C=O$)
Correct Answer: Amino group ($–NH_2$)
Explanation: Amines contain the amino group ($–NH_2$), which consists of a nitrogen atom bonded to two hydrogen atoms. This functional group makes amines basic and capable of forming hydrogen bonds.
46. Which functional group is found in esters?
ⓐ. Carbonyl group ($–C=O$)
ⓑ. Ester group ($–COO–$)
ⓒ. Hydroxyl group ($–OH$)
ⓓ. Amine group ($–NH_2$)
Correct Answer: Ester group ($–COO–$)
Explanation: Esters contain the ester group ($–COO–$), which is formed by the reaction between a carboxylic acid and an alcohol. This functional group gives esters their characteristic fruity smells and is responsible for their use in flavorings and fragrances.
47. What functional group is present in aldehydes?
ⓐ. Amino group ($–NH_2$)
ⓑ. Carbonyl group ($–C=O$)
ⓒ. Hydroxyl group ($–OH$)
ⓓ. Ether group ($–O–$)
Correct Answer: Carbonyl group ($–C=O$)
Explanation: Aldehydes contain a carbonyl group ($–C=O$), where the carbonyl carbon is bonded to one hydrogen atom and one other carbon atom or group. This structure gives aldehydes their characteristic chemical properties.
48. What functional group is present in thiols?
ⓐ. Sulfhydryl group ($–SH$)
ⓑ. Carbonyl group ($–C=O$)
ⓒ. Hydroxyl group ($–OH$)
ⓓ. Amine group ($–NH_2$)
Correct Answer: Sulfhydryl group ($–SH$)
Explanation: Thiols contain the sulfhydryl group ($–SH$), which consists of a sulfur atom bonded to a hydrogen atom. This functional group is responsible for the characteristic odor of thiols and their reactivity in biochemical processes.
49. Which of the following is the functional group in ethers?
ⓐ. Carbonyl group ($–C=O$)
ⓑ. Ether group ($–O–$)
ⓒ. Amine group ($–NH_2$)
ⓓ. Carboxyl group ($–COOH$)
Correct Answer: Ether group ($–O–$)
Explanation: Ethers contain the ether group ($–O–$), which consists of an oxygen atom bonded to two carbon atoms. This functional group is characterized by its ability to act as a solvent and its relatively low reactivity compared to other functional groups.
50. Which of the following is the functional group in alkynes?
ⓐ. Hydroxyl group ($–OH$)
ⓑ. Double bond ($C=C$)
ⓒ. Triple bond ($C≡C$)
ⓓ. Amino group ($–NH_2$)
Correct Answer: Triple bond ($C≡C$)
Explanation: Alkynes contain a triple bond between two carbon atoms ($C≡C$). This functional group gives alkynes their distinct chemical reactivity and is characteristic of this class of hydrocarbons.
51. Which of the following is a characteristic feature of a homologous series?
ⓐ. All compounds in the series have different functional groups.
ⓑ. The compounds differ by a -CH₂ group.
ⓒ. All compounds in the series have the same molecular formula.
ⓓ. The compounds in the series have different chain lengths but the same boiling point.
Correct Answer: The compounds differ by a -CH₂ group.
Explanation: A homologous series is a group of organic compounds that share the same functional group and differ from each other by a -CH₂ unit (methylene group) in their molecular structure. This gives them similar chemical properties and a predictable pattern in physical properties.
52. Which of the following is the first member of the alkane homologous series?
ⓐ. Methane
ⓑ. Ethane
ⓒ. Propane
ⓓ. Butane
Correct Answer: Methane
Explanation: Methane (CH₄) is the first member of the alkane homologous series. Alkanes are saturated hydrocarbons that follow the general formula $C_nH_{2n+2}$, and methane is the simplest alkane with one carbon atom.
53. What is the general molecular formula for alkanes in a homologous series?
ⓐ. $C_nH_{2n}$
ⓑ. $C_nH_{2n+1}$
ⓒ. $C_nH_{2n-2}$
ⓓ. $C_nH_{2n+2}$
Correct Answer: $C_nH_{2n+2}$
Explanation: Alkanes, in a homologous series, follow the general formula $C_nH_{2n+2}$, where $n$ represents the number of carbon atoms. This formula corresponds to saturated hydrocarbons, where each carbon atom is bonded to the maximum number of hydrogen atoms.
54. Which of the following is the functional group in the homologous series of alcohols?
ⓐ. Carbonyl group ($–C=O$)
ⓑ. Hydroxyl group ($–OH$)
ⓒ. Amino group ($–NH_2$)
ⓓ. Ester group ($–COO–$)
Correct Answer: Hydroxyl group ($–OH$)
Explanation: Alcohols form a homologous series where each member contains a hydroxyl group ($–OH$) attached to a carbon atom. The general formula for alcohols is $C_nH_{2n+1}OH$, where the compound differs from the next by a -CH₂ group.
55. Which of the following is the correct IUPAC name for the second member of the alkene homologous series?
ⓐ. Methene
ⓑ. Butene
ⓒ. Propene
ⓓ. Ethene
Correct Answer: Ethene
Explanation: The second member of the alkene homologous series is ethene (C₂H₄). Alkenes are unsaturated hydrocarbons that contain at least one double bond, and they follow the general formula $C_nH_{2n}$.
56. The boiling point of members of a homologous series generally increases with the increase in:
ⓐ. The number of carbon atoms
ⓑ. The number of hydrogen atoms
ⓒ. The number of oxygen atoms
ⓓ. The number of functional groups
Correct Answer: The number of carbon atoms
Explanation: As the number of carbon atoms increases in a homologous series, the size and weight of the molecule increase, leading to stronger van der Waals forces. This results in an increase in boiling points for the members of the homologous series.
57. Which of the following compounds is a member of the alkyl halide homologous series?
ⓐ. CH₄
ⓑ. C₂H₅Cl
ⓒ. C₆H₆
ⓓ. C₂H₄
Correct Answer: C₂H₅Cl
Explanation: C₂H₅Cl (ethyl chloride) is an alkyl halide, which is part of the homologous series of compounds containing a halogen atom (like chlorine) attached to an alkyl group. Alkyl halides have the general formula $C_nH_{2n+1}X$, where X is a halogen.
58. What type of chemical bond is common to all compounds in a homologous series?
ⓐ. Ionic bonds
ⓑ. Covalent bonds
ⓒ. Hydrogen bonds
ⓓ. Metallic bonds
Correct Answer: Covalent bonds
Explanation: All compounds in a homologous series are held together by covalent bonds, where atoms share electrons to form stable molecules. This is true for all organic homologous series, including alkanes, alkenes, alkynes, alcohols, and others.
59. Which of the following is true about members of a homologous series?
ⓐ. They have different molecular formulas but similar chemical properties.
ⓑ. They have the same molecular formula and different chemical properties.
ⓒ. They differ in structure by a single atom.
ⓓ. They have the same functional group and differ by a -CH₂ group.
Correct Answer: They have the same functional group and differ by a -CH₂ group.
Explanation: Members of a homologous series share the same functional group and differ by a -CH₂ group, which gives them similar chemical properties. This characteristic allows for a systematic progression of compounds within the series.
60. Which of the following is the correct IUPAC name for the third member of the alkane homologous series?
ⓐ. Methane
ⓑ. Ethane
ⓒ. Propane
ⓓ. Butane
Correct Answer: Propane
Explanation: Propane (C₃H₈) is the third member of the alkane homologous series. Alkanes follow the general formula $C_nH_{2n+2}$, and propane has three carbon atoms in its chain.
61. What is the correct IUPAC name for the compound with the formula $C_5H_{10}$ and a straight chain of carbon atoms with no double or triple bonds?
ⓐ. Propane
ⓑ. Butane
ⓒ. Pentane
ⓓ. Hexane
Correct Answer: Pentane
Explanation: The compound with the formula $C_5H_{10}$ is an alkane with a straight chain of five carbon atoms. According to IUPAC nomenclature, alkanes are named by the number of carbon atoms in the longest chain. Since there are five carbon atoms, the name is pentane.
62. Which of the following is the correct IUPAC name for the compound with the structure $CH_2=CH-CH_3$?
ⓐ. Ethene
ⓑ. Propene
ⓒ. Butene
ⓓ. Methene
Correct Answer: Propene
Explanation: The compound $CH_2=CH-CH_3$ is an alkene with three carbon atoms and a double bond between the first and second carbon atoms. According to IUPAC rules, alkenes are named by replacing the “-e” of the corresponding alkane with “-ene.” Since this compound has three carbon atoms, it is called propene.
63. Which of the following is the correct IUPAC name for the compound with the structure $CH_3C≡CH$?
ⓐ. Ethyne
ⓑ. Propene
ⓒ. Propyne
ⓓ. Ethene
Correct Answer: Propyne
Explanation: The structure $CH_3C≡CH$ is an alkyne 2121 containing three carbon atoms. The correct IUPAC name is Propyne.
64. What is the IUPAC name for the compound $C_6H_6$?
ⓐ. Cyclohexane
ⓑ. Benzene
ⓒ. Toluene
ⓓ. Cyclohexa-1,3-diene
Correct Answer: Benzene
Explanation: The compound $C_6H_6$ is a simple aromatic hydrocarbon composed of six carbon atoms and six hydrogen atoms, arranged in a hexagonal ring. This structure is called benzene, which is the simplest aromatic hydrocarbon.
65. Which of the following is the correct IUPAC name for the compound with the formula $C_2H_4$?
ⓐ. Methane
ⓑ. Ethane
ⓒ. Propene
ⓓ. Ethene
Correct Answer: Ethene
Explanation: The compound $C_2H_4$ is an alkene with two carbon atoms and a double bond between them. According to IUPAC nomenclature, alkenes are named by replacing the “-e” of the corresponding alkane with “-ene.” Since this compound has two carbon atoms, it is called ethene.
66. Which of the following compounds is named correctly according to IUPAC nomenclature?
ⓐ. 1,2-dimethylpropane
ⓑ. 2-methylbutane
ⓒ. 3-ethylbutene
ⓓ. 1,4-butanediol
Correct Answer: 2-methylbutane
Explanation: 2-methylbutane is correctly named according to IUPAC rules. It is an alkane with five carbon atoms, where a methyl group is attached to the second carbon of a butane chain. The other names either violate chain numbering or contain incorrect functional group placements.
67. What is the IUPAC name for the compound with the structure $CH_3-CH_2-CH_2-CH_3$?
ⓐ. Butane
ⓑ. Propane
ⓒ. Ethane
ⓓ. Methane
Correct Answer: Butane
Explanation: The compound $CH_3-CH_2-CH_2-CH_3$ is an alkane with four carbon atoms in a straight chain. According to IUPAC nomenclature, alkanes are named based on the number of carbon atoms in the longest chain. Since this compound has four carbon atoms, it is called butane.
68. Which of the following is the correct IUPAC name for the compound with the structure $CH_3-CH=CH_2$?
ⓐ. Ethene
ⓑ. Propanol
ⓒ. Butene
ⓓ. Propene
Correct Answer: Propene
Explanation: The answer Propene is correct26. However, the explanation is flawed. According to IUPAC rules, numbering starts from the end closest to the double bond: $C_1H_2=C_2H-C_3H_3$. Therefore, the double bond is between the first and second carbon atoms, not the second and third27.
69. What is the correct IUPAC name for the compound $C_6H_5CH_3$?
ⓐ. Phenol
ⓑ. Toluene
ⓒ. Benzene
ⓓ. Benzenemethanol
Correct Answer: Toluene
Explanation: The compound $C_6H_5CH_3$ consists of a benzene ring ($C_6H_5$) attached to a methyl group ($CH_3$). According to IUPAC nomenclature, this compound is named toluene.
70. What is the correct IUPAC name for the compound $CH_2=CH-CH_2OH$?
ⓐ. Ethanol
ⓑ. Propanol
ⓒ. Propene
ⓓ. Vinyl alcohol
Correct Answer: Vinyl alcohol
Explanation: The provided answer, “Vinyl alcohol,” is incorrect31. Vinyl alcohol is $CH_2=CH-OH$. The structure shown in the question, $CH_2=CH-CH_2OH$, is commonly known as Allyl alcohol. Its correct IUPAC name is Prop-2-en-1-ol, as the main chain is three carbons long with the alcohol on carbon 1 and the double bond on carbon 2.
71. The inductive effect (+I) refers to:
ⓐ. Electron donation through a sigma bond
ⓑ. Electron withdrawal through a pi bond
ⓒ. The movement of electrons in a conjugated system
ⓓ. The donation of lone pair electrons to the molecule
Correct Answer: Electron donation through a sigma bond
Explanation: The +I (positive inductive effect) refers to the electron-donating ability of a substituent or group attached to a molecule through a sigma bond. This effect occurs when a group, such as an alkyl group, donates electron density towards the attached molecule, increasing the electron density of the molecule and stabilizing certain structures, such as carbocations. The +I effect is typically observed in groups with single-bonded carbon atoms like alkyl groups ($–CH_3$, $–C_2H_5$).
72. Which of the following groups exhibits a +I (inductive electron-donating) effect?
ⓐ. $–NO_2$
ⓑ. $–CH_3$
ⓒ. $–COOH$
ⓓ. $–NH_2$
Correct Answer: $–CH_3$
Explanation: The $–CH_3$ (methyl group) exhibits a +I effect because it donates electron density through the sigma bond to the rest of the molecule. This makes the carbon-carbon bond slightly more electron-rich and stabilizes carbocations or other positively charged intermediates. Groups like $–NO_2$ and $–COOH$ withdraw electrons through the inductive effect (–I effect), while $–NH_2$ has a mixed effect but is primarily electron-donating due to the lone pairs on nitrogen.
73. Which of the following is true regarding the –I (inductive electron-withdrawing) effect?
ⓐ. It involves the donation of electrons through a sigma bond.
ⓑ. It makes the molecule electron-rich, stabilizing positive charges.
ⓒ. It pulls electron density towards itself, destabilizing negative charges.
ⓓ. It is observed in groups like $–CH_3$ and $–NH_2$.
Correct Answer: It pulls electron density towards itself, destabilizing negative charges.
Explanation: The –I (negative inductive effect) involves the withdrawal of electron density through a sigma bond, typically by electronegative atoms or groups like halogens ($–Cl$, $–Br$), nitro groups ($–NO_2$), or carbonyl groups ($–C=O$). This withdrawal of electron density can destabilize negative charges (like in carboxylates or alkoxide ions) and makes the molecule more electrophilic, making it prone to attacking nucleophiles.
74. Which of the following functional groups exhibits the strongest –I effect?
ⓐ. $–CH_3$
ⓑ. $–OH$
ⓒ. $–NO_2$
ⓓ. $–NH_2$
Correct Answer: $–NO_2$
Explanation: The $–NO_2$ (nitro group) exhibits the strongest –I effect due to the high electronegativity of nitrogen and the ability of the nitro group to pull electron density through the sigma bond. This effect makes molecules containing the nitro group highly electrophilic, weakening nucleophilic sites and increasing their reactivity in reactions like electrophilic substitution. In contrast, $–CH_3$ (methyl group) and $–NH_2$ (amine group) are electron-donating groups, and $–OH$ (hydroxyl group) has a less pronounced electron-withdrawing effect.
75. Which of the following statements about the –I effect is correct?
ⓐ. It is caused by the withdrawal of electrons from a molecule via the lone pairs of atoms.
ⓑ. The –I effect increases the electron density on a carbon atom attached to the group.
ⓒ. It is observed in highly electronegative groups like halogens and nitro groups.
ⓓ. It makes a molecule more electron-rich, stabilizing negative charges.
Correct Answer: It is observed in highly electronegative groups like halogens and nitro groups.
Explanation: The –I effect is commonly observed in groups such as halogens ($–Cl$, $–Br$, $–I$), nitro groups ($–NO_2$), and carbonyl groups ($–C=O$). These groups are electronegative and tend to withdraw electron density through sigma bonds, making the molecule more electron-deficient and less able to stabilize negative charges. This can make the molecule more susceptible to electrophilic attack.
76. Which of the following functional groups shows the +I effect?
ⓐ. $–OH$
ⓑ. $–NH_2$
ⓒ. $–NO_2$
ⓓ. $–COOH$
Correct Answer: $–NH_2$
Explanation: The $–NH_2$ (amine group) exhibits the +I effect because the nitrogen atom donates electron density through the sigma bond to the rest of the molecule. This electron donation can stabilize carbocations or positively charged intermediates. In contrast, $–OH$ (hydroxyl group) has both +I and –I effects depending on the environment, while $–NO_2$ (nitro group) and $–COOH$ (carboxyl group) are strongly electron-withdrawing due to their high electronegativity.
77. How does the +I effect influence the stability of carbocations?
ⓐ. It destabilizes carbocations by withdrawing electron density.
ⓑ. It only affects the stability of carbanions.
ⓒ. It has no effect on the stability of carbocations.
ⓓ. It stabilizes carbocations by donating electron density.
Correct Answer: It stabilizes carbocations by donating electron density.
Explanation: The +I effect stabilizes carbocations by donating electron density towards the positively charged carbon. This helps to disperse the positive charge, making the carbocation more stable. Alkyl groups, which exhibit a +I effect, are often responsible for stabilizing carbocations in organic reactions like carbocation formation during electrophilic substitution.
78. Which of the following is an example of a group that exhibits the –I effect?
ⓐ. $–CH_3$
ⓑ. $–OH$
ⓒ. $–NO_2$
ⓓ. $–NH_2$
Correct Answer: $–NO_2$
Explanation: The $–NO_2$ (nitro group) exhibits the –I effect due to the high electronegativity of nitrogen and the electron-withdrawing nature of the group. This makes the molecule more electrophilic and less able to stabilize negative charges, which is why the nitro group is often involved in reactions where electron deficiency is favored.
79. How does the +I effect influence the nucleophilicity of a molecule?
ⓐ. It decreases nucleophilicity by pulling electron density away from the molecule.
ⓑ. It only affects electrophilicity, not nucleophilicity.
ⓒ. It has no effect on nucleophilicity.
ⓓ. It increases nucleophilicity by donating electron density to the molecule.
Correct Answer: It increases nucleophilicity by donating electron density to the molecule.
Explanation: The +I effect increases nucleophilicity by donating electron density to the molecule, making the nucleophile more electron-rich and better able to donate electrons in a reaction. Groups like alkyl groups exhibit the +I effect, increasing the nucleophilicity of the molecule to react with electrophiles.
80. Which of the following statements about the inductive effect is correct?
ⓐ. The inductive effect involves the transfer of electrons through a pi bond.
ⓑ. The inductive effect is always the result of a conjugated system.
ⓒ. The inductive effect operates through sigma bonds and affects electron density in molecules.
ⓓ. The inductive effect is only relevant in reactions involving carbon-carbon double bonds.
Correct Answer: The inductive effect operates through sigma bonds and affects electron density in molecules.
Explanation: The inductive effect is the transfer of electron density through sigma bonds. It occurs due to the electronegativity difference between atoms or groups attached to the molecule, which can either donate or withdraw electron density. This effect influences the electron density distribution and reactivity of the molecule in various types of reactions.
81. The mesomeric effect (+M) involves:
ⓐ. Donation of electron density through sigma bonds
ⓑ. Withdrawal of electron density through sigma bonds
ⓒ. Donation of electron density through pi bonds or lone pairs
ⓓ. Withdrawal of electron density through pi bonds or lone pairs
Correct Answer: Donation of electron density through pi bonds or lone pairs
Explanation: The +M (positive mesomeric) effect involves the donation of electron density through pi bonds or lone pairs from a substituent group to the conjugated system of the molecule. This increases electron density in the system, stabilizing reactive intermediates like carbocations or radicals.
82. Which of the following groups exhibits the +M (mesomeric electron-donating) effect?
ⓐ. $–NO_2$
ⓑ. $–CN$
ⓒ. $–NH_2$
ⓓ. $–COOH$
Correct Answer: $–NH_2$
Explanation: The $–NH_2$ (amine) group exhibits a +M effect because the nitrogen atom has lone pairs that can be donated into the conjugated system, increasing electron density in the system. This electron donation stabilizes positive charges and is seen in aromatic compounds like aniline.
83. Which of the following groups exhibits the –M (mesomeric electron-withdrawing) effect?
ⓐ. $–NO_2$
ⓑ. $–NH_2$
ⓒ. $–OH$
ⓓ. $–CH_3$
Correct Answer: $–NO_2$
Explanation: The $–NO_2$ (nitro) group exhibits the –M effect due to the electronegativity of nitrogen and the resonance structure of the nitro group. It withdraws electron density from the conjugated system through pi bonds, making the molecule more electrophilic and stabilizing negative charges.
84. The mesomeric (resonance) effect primarily operates through:
ⓐ. Sigma bonds
ⓑ. Dipole interactions
ⓒ. Ionic interactions
ⓓ. Pi bonds or lone pairs
Correct Answer: Pi bonds or lone pairs
Explanation: The mesomeric (resonance) effect involves the donation or withdrawal of electron density via pi bonds or lone pairs. This effect is seen in conjugated systems where the electron density is delocalized over multiple atoms, typically involving carbon-carbon double bonds or lone pairs from atoms like oxygen, nitrogen, or halogens.
85. Which of the following is the correct description of the –M (mesomeric withdrawing) effect?
ⓐ. It involves the donation of electron density through sigma bonds.
ⓑ. It increases the electron density of the conjugated system.
ⓒ. It involves the withdrawal of electron density through pi bonds or lone pairs.
ⓓ. It makes the molecule electron-rich, stabilizing positive charges.
Correct Answer: It involves the withdrawal of electron density through pi bonds or lone pairs.
Explanation: The –M (mesomeric withdrawing) effect occurs when a substituent group withdraws electron density from the conjugated system through pi bonds or lone pairs. This reduces electron density in the system, which can make the molecule more electrophilic and stabilize negative charges.
86. Which of the following groups has both +M and –I effects?
ⓐ. $–OH$
ⓑ. $–CH_3$
ⓒ. $–NO_2$
ⓓ. $–COOH$
Correct Answer: $–OH$
Explanation: The $–OH$ (hydroxyl) group exhibits both +M and –I effects. The lone pairs on oxygen donate electron density through resonance (mesomeric effect, +M), but oxygen is also electronegative, which withdraws electron density via induction (–I). The overall effect depends on the structure of the molecule, but generally, the +M effect predominates.
87. Which of the following functional groups exhibits a strong –M (mesomeric electron-withdrawing) effect in an aromatic compound?
ⓐ. $–NH_2$
ⓑ. $–OH$
ⓒ. $–NO_2$
ⓓ. $–CH_3$
Correct Answer: $–NO_2$
Explanation: The $–NO_2$ (nitro) group exhibits a strong –M effect in aromatic compounds. The nitro group pulls electron density away from the ring through resonance, making the molecule more electrophilic and decreasing the electron density on the aromatic ring. This effect is why the nitro group deactivates the ring towards electrophilic substitution reactions.
88. In the resonance structure of an aromatic compound, which type of atoms or groups can donate electron density through mesomeric effects?
ⓐ. Highly electronegative atoms like halogens
ⓑ. Atoms with lone pairs like oxygen or nitrogen
ⓒ. Alkyl groups
ⓓ. None of the above
Correct Answer: Atoms with lone pairs like oxygen or nitrogen
Explanation: Atoms with lone pairs, such as oxygen, nitrogen, and halogens, can donate electron density through mesomeric (resonance) effects. This donation stabilizes positive charges or carbocations and increases electron density in the conjugated system, such as in compounds like aniline ($–NH_2$) or phenol ($–OH$).
89. The –M (mesomeric electron-withdrawing) effect makes the molecule:
ⓐ. More electron-rich and reactive towards nucleophiles
ⓑ. More electron-deficient and reactive towards electrophiles
ⓒ. Less reactive in both nucleophilic and electrophilic reactions
ⓓ. Neutral with no effect on reactivity
Correct Answer: More electron-deficient and reactive towards electrophiles
Explanation: The –M effect withdraws electron density from the conjugated system, making the molecule more electron-deficient. This increases its electrophilicity, making it more reactive towards nucleophiles in electrophilic substitution reactions, like those in aromatic compounds.
90. Which of the following functional groups exhibits a +M (mesomeric electron-donating) effect in an aromatic compound?
ⓐ. $–COOH$
ⓑ. $–NO_2$
ⓒ. $–NH_2$
ⓓ. $–CF_3$
Correct Answer: $–NH_2$
Explanation: The $–NH_2$ (amine) group exhibits a +M effect in aromatic compounds because the nitrogen atom donates electron density through its lone pair into the conjugated pi system. This increases the electron density on the aromatic ring, making it more reactive in electrophilic aromatic substitution reactions.
91. The phenomenon of hyperconjugation is also known as:
ⓐ. No-bond resonance
ⓑ. Pi-pi interaction
ⓒ. Sigma-pi interaction
ⓓ. Bond polarization
Correct Answer: No-bond resonance
Explanation: Hyperconjugation, also referred to as no-bond resonance, occurs when electron density from a sigma bond (usually C-H or C-C) is delocalized into an adjacent empty or partially filled orbital (typically a π-orbital or antibonding σ-orbital). This delocalization stabilizes the molecule, especially carbocations and free radicals.
92. Which of the following factors increases the hyperconjugation effect?
ⓐ. Presence of lone pairs on adjacent atoms
ⓑ. The number of alkyl groups attached to the carbocation
ⓒ. Presence of a double bond adjacent to the carbon-carbon bond
ⓓ. Presence of a hydroxyl group adjacent to the structure
Correct Answer: The number of alkyl groups attached to the carbocation
Explanation: The hyperconjugation effect is enhanced by the presence of more alkyl groups attached to the carbocation. Alkyl groups donate electron density through their sigma bonds, which stabilizes the positive charge on the carbocation. This is why tertiary carbocations (with three alkyl groups) are more stable than secondary or primary ones.
93. Which of the following species is most stabilized by hyperconjugation?
ⓐ. Tertiary carbocation
ⓑ. Primary carbocation
ⓒ. Ethene
ⓓ. Propanol
Correct Answer: Tertiary carbocation
Explanation: Hyperconjugation provides stability to carbocations by delocalizing electron density from adjacent C-H or C-C bonds into the empty p-orbital of the carbocation. Tertiary carbocations, which have three alkyl groups attached to the positively charged carbon, experience the maximum hyperconjugation effect, making them the most stable.
94. In which of the following compounds is the hyperconjugation effect observed?
ⓐ. Ethyl alcohol
ⓑ. Ethene
ⓒ. Tert-butyl carbocation
ⓓ. Benzene
Correct Answer: Tert-butyl carbocation
Explanation: Hyperconjugation is observed in species like the tert-butyl carbocation, where the positive charge on the carbon atom is stabilized by electron donation from adjacent C-H bonds. This effect is not significant in compounds like ethyl alcohol, ethene, or benzene, as they do not have the required structure for hyperconjugation.
95. Hyperconjugation is most effective when:
ⓐ. The adjacent bonds are sigma bonds
ⓑ. The structure contains a double bond or a triple bond
ⓒ. There are no alkyl groups attached to the conjugated system
ⓓ. The molecule has only single bonds
Correct Answer: The adjacent bonds are sigma bonds
Explanation: Hyperconjugation is most effective when the adjacent bonds to a carbocation or free radical are sigma bonds, especially C-H or C-C bonds. The delocalization of electron density from these sigma bonds into empty or partially filled orbitals (such as a π-orbital) helps stabilize the molecule.
96. Which of the following statements is true about hyperconjugation?
ⓐ. Hyperconjugation can only occur in conjugated systems.
ⓑ. Hyperconjugation is a type of pi-pi interaction.
ⓒ. Hyperconjugation helps stabilize carbocations and free radicals.
ⓓ. Hyperconjugation is unrelated to the presence of alkyl groups.
Correct Answer: Hyperconjugation helps stabilize carbocations and free radicals.
Explanation: Hyperconjugation is particularly important in stabilizing carbocations, free radicals, and alkenes. It involves the delocalization of electron density from adjacent sigma bonds (typically C-H or C-C) into an empty or partially filled orbital. This delocalization stabilizes positively charged or radical species.
97. Which of the following structures exhibits the strongest hyperconjugation effect?
ⓐ. CH₃CH₂+
ⓑ. CH₃CH₂OH
ⓒ. CH₂=CH₂
ⓓ. (CH₃)₃C+
Correct Answer: (CH₃)₃C+
Explanation: The tert-butyl carbocation, (CH₃)₃C+, exhibits the strongest hyperconjugation effect because it has three methyl groups attached to the positively charged carbon. Each of these methyl groups donates electron density through their sigma bonds, which stabilizes the carbocation and makes it the most stable compared to the other species.
98. Which of the following correctly describes the mechanism of hyperconjugation?
ⓐ. It involves the donation of lone pair electrons into an empty orbital.
ⓑ. It involves the donation of electrons from a pi bond into a sigma bond.
ⓒ. It involves the formation of a double bond between adjacent atoms.
ⓓ. It involves the delocalization of electron density from a sigma bond into an adjacent empty or partially filled orbital.
Correct Answer: It involves the delocalization of electron density from a sigma bond into an adjacent empty or partially filled orbital.
Explanation: Hyperconjugation involves the delocalization of electron density from a sigma bond, typically C-H or C-C, into an adjacent empty or partially filled orbital. This phenomenon provides stability to reactive intermediates like carbocations and free radicals.
99. In which of the following species is hyperconjugation NOT possible?
ⓐ. Tert-butyl carbocation
ⓑ. Ethyl free radical
ⓒ. Propane
ⓓ. Methyl carbocation
Correct Answer: Propane
Explanation: Hyperconjugation is not possible in propane because there are no reactive intermediates such as carbocations or free radicals. Hyperconjugation occurs in species with an empty or partially filled orbital, such as carbocations, free radicals, and alkenes. Propane is a simple alkane with no such structure.
100. Hyperconjugation can be explained as:
ⓐ. The donation of electrons from a pi bond to an adjacent sigma bond.
ⓑ. The delocalization of electrons from a sigma bond to an adjacent empty or partially filled orbital.
ⓒ. The formation of a new bond between two atoms.
ⓓ. The stabilization of a molecule due to the overlap of lone pairs.
Correct Answer: The delocalization of electrons from a sigma bond to an adjacent empty or partially filled orbital.
Explanation: Hyperconjugation is the delocalization of electron density from a sigma bond, typically a C-H or C-C bond, into an adjacent empty or partially filled orbital, such as a pi-orbital or an antibonding sigma-orbital. This effect helps stabilize reactive intermediates like carbocations or free radicals.
Welcome to Class 11 Chemistry MCQs – Chapter 12: Organic Chemistry – Some Basic Principles and Techniques (Part of 3). This is one of the most important chapters in NCERT Class 11 Chemistry, forming the foundation of all future Organic Chemistry topics. Here you’ll find 100 carefully selected MCQs with detailed answers designed for Board Exams, JEE Main, JEE Advanced, NEET, and other competitive tests. These questions cover everything from IUPAC nomenclature rules to reaction mechanisms and electronic effects, ensuring complete conceptual clarity.
Navigation & Parts: The chapter includes 300 MCQs divided into 3 parts (100 + 100 + 100). This page contains the first 100 MCQs with explanations. Use the Part buttons above to continue through the next sets of questions.
What you will learn & practice (Chapter 12 Highlights)
- General introduction to Organic Chemistry and its scope in modern science
- Classification of organic compounds and identification based on functional groups
- IUPAC nomenclature of alkanes, alkenes, alkynes, and aromatic compounds
- Electronic displacement effects — inductive, resonance, electromeric and hyperconjugation effects
- Reaction mechanisms and types of intermediates — carbocations, carbanions, free radicals
- Methods of purification of organic compounds — crystallization, sublimation, distillation & chromatography
- Detection of elements in organic compounds (C, H, N, S, halogens tests)
- Qualitative & quantitative analysis — Liebig’s, Dumas & Kjeldahl methods
- Concept of isomerism and hybridization in organic molecules
- Real-exam problems on structure, bonding & mechanistic pathways
How to use this site to practice Organic Chemistry MCQs
- Start slow (10 mins): Glance through key topics like IUPAC rules and electronic effects before attempting questions.
- Active practice: Solve 10–20 MCQs in each session and read explanations carefully to understand reaction logic.
- Use ❤️ Favourite: Click the Heart beside any important question to save it for quick revision; activate the Favourite Toggle to see only saved ones.
- Write Workspace notes: Under each question click Workspace to record shortcuts or mechanism steps — notes auto-save and stay secure.
- Shuffle & test: Use Random to re-attempt mixed questions and avoid pattern memory.
- Smart revision: Revisit your ❤️ Favourites on Day 2, 4 & 7 to reinforce concepts before exams.
Why this chapter matters for Boards & Competitive Exams
- Boards: Direct MCQs on IUPAC nomenclature, functional groups & tests for elements are frequent.
- JEE Main & Advanced: Mechanism-based and reaction-type MCQs on carbocations & electron effects repeat every year.
- NEET: Questions on organic analysis, isomerism, and purification are high-scoring and concept-driven.
- Tip: Combine the Favourite and Workspace features for your personalized organic revision sheet.
Common mistakes to avoid
- Confusing between parent chain and substituents during IUPAC naming
- Ignoring electronic effects while predicting stability of intermediates
- Mixing up distillation types in purification techniques
- Forgetting stoichiometric steps in Dumas & Kjeldahl methods
- Not linking hybridization with molecular geometry in bonding questions
Think of this page as your Organic Chemistry playground — solve, mark, note, repeat. Each question you answer correctly adds confidence for Boards & entrance exams. Keep your ❤️ list and Workspace updated for quick revisions anytime.
Explore more: Class 11 Chemistry – Chapter Index, Class 11 – Subject Index, All Classes – MCQ Library.
Quick FAQ
Is Organic Chemistry hard in Class 11?
Initially yes, but once you grasp the basics of nomenclature and electronic effects, it becomes logical and fun. Consistent MCQ practice is key.
How many MCQs should I solve daily?
Start with 20–30 MCQs a day, mark important ones as ❤️ Favourite and revisit them regularly for revision.
How can I revise quickly before exam?
Activate the Favourite Toggle to see only your marked MCQs and skim your Workspace notes for a 1-hour final revision session.
- 👉 Total MCQs in this chapter: 300 (100 + 100 + 100)
- 👉 This page: First 100 MCQs with answers & explanations
- 👉 Best for: Boards • JEE/NEET • IUPAC nomenclature • reaction mechanisms • organic analysis practice
- 👉 Next: Use the Part buttons and page numbers above to continue
FAQs on Organic Chemistry ▼
▸ What are Organic Chemistry MCQs in Class 11 Chemistry?
These are multiple-choice questions from Chapter 12 of NCERT Class 11 Chemistry – Organic Chemistry. They assess your understanding of structure and bonding, hybridization, IUPAC nomenclature, isomerism, and basics of reaction mechanisms.
▸ How many MCQs are available in this chapter?
There are a total of 300 Organic Chemistry MCQs. They are divided into 3 structured parts – three sets of 100 questions each.
▸ Are Organic Chemistry MCQs important for JEE and NEET?
Yes, this chapter is crucial for JEE and NEET. Frequently tested areas include IUPAC nomenclature, GOC (inductive, resonance/mesomeric, hyperconjugation), acidity/basicity trends, reaction intermediates (carbocation, carbanion, free radical), and common mechanisms like SN1, SN2, E1, E2, and electrophilic addition.
▸ Do these MCQs include correct answers and explanations?
Yes, every MCQ is accompanied by the correct answer and detailed explanations to build concept clarity and improve speed and accuracy in exams.
▸ Which subtopics are covered in these Organic Chemistry MCQs?
Subtopics include structure and bonding, hybridization and resonance, IUPAC nomenclature, classification of organic compounds, isomerism (structural and basic stereochemistry), electronic effects (inductive, mesomeric/resonance, hyperconjugation), reaction mechanism basics, reaction intermediates, types of organic reactions (substitution, addition, elimination, rearrangements), and purification/analysis methods (crystallization, distillation, chromatography, Lassaigne’s tests).