1. A haloalkane is best described as a compound in which:
ⓐ. a halogen is bonded directly to an aromatic-ring carbon
ⓑ. a halogen is bonded to a carbon atom of an alkyl group
ⓒ. a halogen is present only as a free halide ion
ⓓ. a halogen is bonded exclusively to an oxygen atom
Correct Answer: a halogen is bonded to a carbon atom of an alkyl group
Explanation: A haloalkane is obtained when one or more hydrogen atoms of an aliphatic hydrocarbon are replaced by halogen atoms. The halogen is attached to a carbon belonging to an alkyl framework. Compounds such as \(\mathrm{CH_3Cl}\) and \(\mathrm{C_2H_5Br}\) belong to this family. A halogen attached directly to an aromatic ring produces a haloarene instead. The attachment site, rather than the mere presence of a halogen, determines the compound class.
2. Which set contains only the halogens commonly considered in haloalkanes and haloarenes?
ⓐ. \(\mathrm{O,\ S,\ Se,\ Te}\)
ⓑ. \(\mathrm{N,\ P,\ As,\ Sb}\)
ⓒ. \(\mathrm{F,\ Cl,\ Br,\ I}\)
ⓓ. \(\mathrm{C,\ Si,\ Ge,\ Sn}\)
Correct Answer: \(\mathrm{F,\ Cl,\ Br,\ I}\)
Explanation: Fluorine, chlorine, bromine, and iodine are the halogens used in the usual classification of organic halo compounds. They belong to Group \(17\) of the periodic table. Their compounds are called fluoro, chloro, bromo, and iodo derivatives, respectively. Oxygen and sulfur belong to Group \(16\), while nitrogen and phosphorus belong to Group \(15\). The four halogens differ in size and bond properties, but all can form carbon–halogen bonds.
3. Among the following compounds, the one having its halogen directly attached to an aromatic ring is:
ⓐ. \(\mathrm{CH_3CH_2Cl}\)
ⓑ. \(\mathrm{C_6H_5Br}\)
ⓒ. \(\mathrm{C_6H_5CH_2Cl}\)
ⓓ. \(\mathrm{CH_2{=}CHCH_2Br}\)
Correct Answer: \(\mathrm{C_6H_5Br}\)
Explanation: In \(\mathrm{C_6H_5Br}\), bromine is bonded directly to a carbon atom of the benzene ring, so the compound is a haloarene. In \(\mathrm{C_6H_5CH_2Cl}\), chlorine is attached to a side-chain carbon next to the ring. \(\mathrm{CH_3CH_2Cl}\) is an ordinary haloalkane, while \(\mathrm{CH_2{=}CHCH_2Br}\) contains bromine on a carbon adjacent to a double bond. An aromatic ring somewhere in the molecule is not sufficient; the halogen must be directly attached to that ring.
4. Replacing one hydrogen atom of ethane, \(\mathrm{C_2H_6}\), by one bromine atom gives the molecular formula:
ⓐ. \(\mathrm{C_2H_5Br}\)
ⓑ. \(\mathrm{C_2H_6Br}\)
ⓒ. \(\mathrm{C_2H_4Br}\)
ⓓ. \(\mathrm{C_2H_5Br_2}\)
Correct Answer: \(\mathrm{C_2H_5Br}\)
Explanation: Ethane initially contains two carbon atoms and six hydrogen atoms. Replacement means that one hydrogen atom is removed and one bromine atom occupies its position. The carbon count remains \(\mathrm{C_2}\), while the hydrogen count decreases from \(\mathrm{H_6}\) to \(\mathrm{H_5}\). Only one bromine atom is introduced, giving \(\mathrm{C_2H_5Br}\). Adding bromine without removing hydrogen would not represent a substitution product.
5. A broad description of the practical importance of halo compounds is that:
ⓐ. selected halo compounds serve only as fuels and never as chemical intermediates
ⓑ. all halo compounds act as medicines because halogenation guarantees biological activity
ⓒ. halo compounds are restricted to small-scale reagents and have no industrial applications
ⓓ. selected halo compounds have solvent, medical, synthetic, and industrial uses
Correct Answer: selected halo compounds have solvent, medical, synthetic, and industrial uses
Explanation: Halo compounds form a chemically diverse group with many applications. Some have been used as solvents, refrigerants, pesticides, medicines, or intermediates in organic synthesis. Their suitability depends on molecular structure, physical properties, reactivity, toxicity, and environmental behaviour. The presence of a halogen alone does not guarantee a particular use. It is also inaccurate to assume that every member of the family is safe or biologically useful.
6. Read the following statements about halo compounds.
Statement I: They may be formed by replacing one or more hydrogen atoms of a hydrocarbon with halogen atoms.
Statement II: Every halo compound must contain an aromatic ring.
Statement III: The family includes both haloalkanes and haloarenes.
ⓐ. Statement I only
ⓑ. Statement II only
ⓒ. Statements I and III only
ⓓ. Statements II and III only
Correct Answer: Statements I and III only
Explanation: Organic halo compounds can be viewed as derivatives of hydrocarbons in which one or more hydrogen atoms have been replaced by halogens. Haloalkanes arise from aliphatic carbon skeletons, whereas haloarenes contain halogen directly bonded to an aromatic ring. An aromatic ring is therefore required for a haloarene but not for every halo compound. Compounds such as \(\mathrm{CH_3Cl}\) contain no aromatic ring and are still organic halo compounds. Statement II incorrectly applies the defining feature of haloarenes to the entire family.
7. Match each symbol in Column I with its meaning in Column II.
| Column I | Column II |
|---|
| P. \(\mathrm{R}\) | 1. Halogen atom |
| Q. \(\mathrm{Ar}\) | 2. Aryl group |
| R. \(\mathrm{X}\) | 3. Alkyl group |
| S. \(\mathrm{Ar-X}\) | 4. General haloarene notation |
ⓐ. P-2, Q-3, R-1, S-4
ⓑ. P-3, Q-2, R-1, S-4
ⓒ. P-3, Q-1, R-2, S-4
ⓓ. P-1, Q-2, R-4, S-3
Correct Answer: P-3, Q-2, R-1, S-4
Explanation: The symbol \(\mathrm{R}\) represents an alkyl group, so P matches 3. The symbol \(\mathrm{Ar}\) represents an aryl group derived from an aromatic system, so Q matches 2. The symbol \(\mathrm{X}\) stands for a halogen atom, giving R-1. Combining an aryl group with a halogen gives the general haloarene notation \(\mathrm{Ar-X}\), so S matches 4. Confusing \(\mathrm{R}\) with \(\mathrm{Ar}\) changes an aliphatic structure into an aromatic one.
8. A molecule contains a carbon–chlorine bond. What additional structural information is needed to classify it as a haloarene rather than a haloalkane?
ⓐ. The molecule must contain at least one carbon–carbon single bond
ⓑ. Chlorine must be more electronegative than carbon
ⓒ. Chlorine must be attached directly to an aromatic-ring carbon
ⓓ. The molecule must contain at least one hydrogen atom
Correct Answer: Chlorine must be attached directly to an aromatic-ring carbon
Explanation: Both haloalkanes and haloarenes contain carbon–halogen bonds, so the bond alone does not establish the class. A haloarene requires chlorine to be bonded directly to a carbon that forms part of an aromatic ring. If chlorine is attached to an alkyl side chain, the compound is treated as a haloalkane or a specialised side-chain derivative. Electronegativity does not distinguish these structural classes because chlorine is more electronegative than carbon in both cases. Classification depends on the identity and location of the bonded carbon atom.
9. A carbon skeleton containing only carbon–carbon single bonds is described as saturated, whereas the presence of a carbon–carbon double bond makes it:
ⓐ. unsaturated
ⓑ. aromatic in every case
ⓒ. ionic
ⓓ. fully hydrogenated
Correct Answer: unsaturated
Explanation: A saturated carbon skeleton contains only single bonds between its carbon atoms. Such carbon atoms ordinarily carry the maximum number of hydrogen atoms permitted by the bonding framework. A carbon–carbon double or triple bond introduces unsaturation. Unsaturation does not automatically make a compound aromatic, because ordinary alkenes are unsaturated but non-aromatic. This distinction becomes useful when identifying whether a halogen is attached to or positioned next to a multiple bond.
10. The carbon atoms joined by the double bond in ethene, \(\mathrm{CH_2{=}CH_2}\), are:
ⓐ. \(\mathrm{sp}\)-hybridised
ⓑ. \(\mathrm{sp^2}\)-hybridised
ⓒ. \(\mathrm{sp^3}\)-hybridised
ⓓ. alternately \(\mathrm{sp}\)- and \(\mathrm{sp^3}\)-hybridised
Correct Answer: \(\mathrm{sp^2}\)-hybridised
Explanation: Each carbon atom in ethene forms three sigma-bonding directions and retains one unhybridised \(p\) orbital. The three sigma-bonding orbitals arise from \(\mathrm{sp^2}\) hybridisation. Sidewise overlap of the unhybridised \(p\) orbitals forms the pi component of the double bond. By contrast, a carbon forming four ordinary single bonds is generally \(\mathrm{sp^3}\)-hybridised. Hybridisation is determined by the local bonding arrangement rather than by the total number of atoms in the molecule.
11. A carbon atom is bonded to one other carbon atom and three hydrogen atoms. On the basis of its carbon attachments, it is a:
ⓐ. quaternary carbon
ⓑ. tertiary carbon
ⓒ. secondary carbon
ⓓ. primary carbon
Correct Answer: primary carbon
Explanation: The degree of a carbon atom is determined by the number of other carbon atoms directly bonded to it. A carbon attached to one other carbon is primary, written as \(1^\circ\). Attachment to two or three carbons would make it secondary or tertiary, respectively. The three hydrogen atoms do not increase the carbon degree because only carbon neighbours are counted. A methyl carbon attached to no other carbon is treated as a separate limiting case rather than as a primary carbon.
12. In the fragment \(\mathrm{(CH_3)_3C-}\), the central carbon is classified as:
ⓐ. a tertiary carbon
ⓑ. a primary carbon
ⓒ. a secondary carbon
ⓓ. a methyl carbon
Correct Answer: a tertiary carbon
Explanation: The central carbon in \(\mathrm{(CH_3)_3C-}\) is directly bonded to three methyl carbon atoms. Carbon degree is based on the number of direct carbon neighbours, so this centre is tertiary. The free valence may later form a bond to a non-carbon substituent such as a halogen without changing the three carbon attachments. The methyl groups around it are primary carbon centres, but the central carbon is not. Overall molecular branching should not be confused with the degree of the specific carbon being examined.
13. In the fragment \(\mathrm{R-CH_2-CH_2-X}\), the carbon directly bonded to \(\mathrm{X}\) and the next carbon along the chain are called, respectively:
ⓐ. two \(\alpha\)-carbons
ⓑ. two \(\beta\)-carbons
ⓒ. the \(\alpha\)-carbon and the \(\beta\)-carbon
ⓓ. the \(\beta\)-carbon and the \(\alpha\)-carbon
Correct Answer: the \(\alpha\)-carbon and the \(\beta\)-carbon
Explanation: Carbon positions are labelled relative to the functional group or substituent being considered. The carbon directly bonded to \(\mathrm{X}\) is the \(\alpha\)-carbon. The adjacent carbon is the \(\beta\)-carbon, and positions farther away may be labelled \(\gamma\), \(\delta\), and so on. These labels describe position rather than carbon degree. A carbon may be both an \(\alpha\)-carbon and a primary, secondary, or tertiary carbon depending on its other carbon attachments.
14. During a reaction, one species donates an electron pair to an electron-deficient carbon centre. The roles of the two participants are:
ⓐ. the donor is an electrophile, and the carbon centre is a nucleophile
ⓑ. the donor is a nucleophile, and the carbon centre is an electrophile
ⓒ. both participants are nucleophiles
ⓓ. both participants are electrophiles
Correct Answer: the donor is a nucleophile, and the carbon centre is an electrophile
Explanation: A nucleophile is an electron-pair donor that seeks an electron-deficient centre. An electrophile accepts an electron pair and is commonly associated with partial or complete positive charge. Species such as \(\mathrm{OH^-}\), \(\mathrm{CN^-}\), and \(\mathrm{NH_3}\) can act as nucleophiles because they possess available electron pairs. The electron-deficient carbon accepts the pair during bond formation and therefore behaves as the electrophile. The terms describe complementary electronic roles rather than fixed classes of elements.
15. An aromatic-ring carbon in benzene belongs to an aryl skeleton and has which hybridisation?
ⓐ. alkyl skeleton and \(\mathrm{sp^3}\) hybridisation
ⓑ. alkyl skeleton and \(\mathrm{sp^2}\) hybridisation
ⓒ. aryl skeleton and \(\mathrm{sp^2}\) hybridisation
ⓓ. aryl skeleton and \(\mathrm{sp^3}\) hybridisation
Correct Answer: aryl skeleton and \(\mathrm{sp^2}\) hybridisation
Explanation: Benzene is an aromatic compound, and removal of one ring hydrogen gives an aryl group such as \(\mathrm{C_6H_5-}\). Each carbon atom in the benzene ring is \(\mathrm{sp^2}\)-hybridised. The remaining unhybridised \(p\) orbitals overlap to form the delocalised aromatic pi system. Alkyl groups are derived from aliphatic hydrocarbons and commonly contain \(\mathrm{sp^3}\)-hybridised saturated carbon centres. Aromatic identity and carbon hybridisation must be read from the local bonding structure, not merely from the number of carbon atoms.
16. A molecule has the formula \(\mathrm{CH_2ClCH_2Br}\). Its most suitable classification by halogen count is:
ⓐ. monohalo because it contains only one chlorine atom
ⓑ. trihalo because it contains two carbons and one bromine atom
ⓒ. polyhalo but not dihalo because the halogens are different
ⓓ. dihalo because it contains two halogen atoms
Correct Answer: dihalo because it contains two halogen atoms
Explanation: The molecule contains one chlorine atom and one bromine atom. Both are halogens, so the total halogen count is two. A dihalo compound need not contain two identical halogen atoms. The number of carbon atoms does not enter into the mono-, di-, or trihalo classification. Treating chlorine and bromine separately would overlook that both belong to the same halogen family.
17. Judge the following statements.
Statement I: A dihalo compound may contain two identical halogen atoms.
Statement II: A dihalo compound may contain two different halogen atoms.
Statement III: Every dihalo compound must contain exactly two carbon atoms.
ⓐ. Statements I and III only
ⓑ. Statements I and II only
ⓒ. Statements II and III only
ⓓ. Statements I, II and III
Correct Answer: Statements I and II only
Explanation: A dihalo compound is defined by the presence of two halogen atoms in one molecule. The two atoms may be identical, as in \(\mathrm{CH_2Cl_2}\), or different, as in \(\mathrm{CH_2ClBr}\). The carbon skeleton may contain one, two, or many carbon atoms. Statement III incorrectly connects the prefix “di” with the number of carbon atoms. In this classification, “di” modifies the halogen substituent count alone.
18. Match each molecular formula in Column I with its classification in Column II.
| Column I | Column II |
|---|
| P. \(\mathrm{CH_3Cl}\) | 1. Trihalo compound |
| Q. \(\mathrm{CH_2Cl_2}\) | 2. Monohalo compound |
| R. \(\mathrm{CHCl_3}\) | 3. Tetrahalo compound |
| S. \(\mathrm{CCl_4}\) | 4. Dihalo compound |
ⓐ. P-4, Q-2, R-1, S-3
ⓑ. P-2, Q-1, R-4, S-3
ⓒ. P-2, Q-4, R-1, S-3
ⓓ. P-1, Q-4, R-3, S-2
Correct Answer: P-2, Q-4, R-1, S-3
Explanation: \(\mathrm{CH_3Cl}\) contains one chlorine atom and is monohalo, so P matches 2. \(\mathrm{CH_2Cl_2}\) contains two chlorine atoms and is dihalo, giving Q-4. \(\mathrm{CHCl_3}\) has three chlorine atoms and is trihalo, so R-1. \(\mathrm{CCl_4}\) contains four chlorine atoms and is tetrahalo, giving S-3. Reading the subscript on the halogen symbol is more reliable than judging the class from the number of hydrogen atoms remaining.
19. A compound contains five carbon atoms, eleven hydrogen atoms, and one bromine atom. Its classification by halogen count is:
ⓐ. pentahalo because it has five carbon atoms
ⓑ. polyhalo because its total atom count is greater than four
ⓒ. dihalo because carbon and bromine are both counted
ⓓ. monohalo because only one halogen atom is present
Correct Answer: monohalo because only one halogen atom is present
Explanation: Only atoms belonging to the halogen family are counted in this classification. The compound has a single bromine atom, so it is monohalo. Its five-carbon skeleton affects its hydrocarbon name but not the halo-count prefix. Hydrogen atoms are likewise irrelevant to the mono-, di-, or trihalo label. A long carbon chain can still carry only one halogen substituent.
20. In \(\mathrm{CH_3-CBr_2-CH_3}\), the arrangement of the bromine atoms and the degree of the bromine-bearing carbon are, respectively:
ⓐ. geminal and secondary
ⓑ. vicinal and secondary
ⓒ. geminal and tertiary
ⓓ. vicinal and primary
Correct Answer: geminal and secondary
Explanation: Both bromine atoms are bonded to the same central carbon, so the compound is a geminal dihalide. A vicinal dihalide would have the two bromine atoms on adjacent carbon atoms. The bromine-bearing carbon is directly attached to two other carbon atoms, one on each side. It is therefore a secondary carbon. The terms geminal and secondary describe two different structural features: halogen arrangement and carbon degree.
