Haloalkanes and Haloarenes Mock Test – Class 12 Chemistry

1. Assertion: Bromobenzene can form phenylmagnesium bromide even though it resists ordinary nucleophilic substitution.
Reason: Grignard-reagent formation does not require either a free phenyl carbocation or normal backside nucleophilic attack at the aromatic carbon.

2. In the fragment , the central carbon is classified as:

3. A sample contains of one enantiomer of -chlorobutane and of its mirror-image form. Its net optical rotation is expected to be:

4. The claim “Choosing a polar aprotic solvent is sufficient to make every haloalkane react by ” is:

5. A mechanism-selection guide contains three entries.
P. Primary haloalkane, strong compact nucleophile, polar aprotic solvent —
Q. Tertiary haloalkane, strong base, heat — elimination
R. Tertiary haloalkane, weak neutral nucleophile, polar protic solvent — competition

How should the entries be evaluated?

6. Assertion: The Wurtz reaction is most suitable for preparing symmetrical alkanes.
Reason: Using two different alkyl halides can produce two symmetrical coupling products and one cross-coupled product.

7. Assertion: Thionyl chloride is commonly preferred over many phosphorus chlorides for preparing a pure alkyl chloride.
Reason: The and produced during the reaction can leave the mixture as gases.

8. Propene reacts with under ordinary conditions and in the absence of peroxides. The major product is:

9. Match each property in Column I with the appropriate description in Column II.

10. The carbon–chlorine bond in chlorobenzene is shorter and stronger than the corresponding bond in chloroethane mainly because:

11. Nitration of chlorobenzene produces both ortho- and para-substituted products, with the para isomer often present in the larger amount. Which explanation accounts for this result?

12. A chemist records the following structures:
P.
Q.
R.

The classifications of P, Q, and R are, respectively:

13. Direct fluorination of an alkane is generally avoided as a controlled laboratory method for preparing a specific alkyl fluoride because:

14. Benzyl chloride and chlorobenzene differ because:

15. The claim “Dichloromethane evaporates readily, so it cannot remain long enough to cause exposure” is:

16. Ethanol is often added in small quantity to stored chloroform because ethanol:

17. The enhanced stability of a benzyl carbocation arises because:

18. Replacement of an aromatic diazonium group is strongly favoured because the leaving species formed is:

19. Evaluate the following statements about aromatic diazonium salts.
Statement I: They are commonly prepared from primary aromatic amines.
Statement II: Their preparation is carried out at low temperature.
Statement III: Replacement of the diazonium group occurs without liberation of nitrogen gas.

20. The common name “methylene chloride” refers to:

21. The carbon atoms joined by the double bond in ethene, , are:

22. The rise in boiling point from an alkyl chloride to the corresponding alkyl iodide is mainly associated with:

23. Carbocation stabilisation by ordinary alkyl groups is described below.
P. Methyl carbocation — no alkyl-group donation
Q. Primary alkyl carbocation — one alkyl group provides limited stabilisation
R. Secondary alkyl carbocation — two alkyl groups provide greater stabilisation
S. Tertiary alkyl carbocation — three alkyl groups provide the greatest ordinary alkyl stabilisation

Select the appropriate evaluation.

24. Chlorobenzene undergoes nitration more slowly than benzene but gives mainly ortho- and para-substituted products. The best combined explanation is:

25. When chlorobenzene is heated with aqueous sodium hydroxide at about under high pressure, the immediate organic product is:

26. Analyse the following energy-profile interpretations.

Which evaluation is appropriate?

27. Water and chloroform are placed in a separatory funnel and allowed to settle. Chloroform forms the lower layer mainly because it is:

28. Iodide is generally a better leaving group than fluoride because:

29. A reaction-coordinate graph for benzene chlorination shows two pathways with the same reactant and product energy levels. The curve for the -catalysed pathway has a lower maximum than the uncatalysed curve. The graph indicates that :

30. Under conditions in which carbon–halogen bond ionisation is significant, allyl chloride generally reacts more readily than -chloropropane because:

31. Assertion: Anhydrous increases the reactivity of an alcohol toward concentrated hydrochloric acid.
Reason: acts as a Lewis acid and coordinates with the alcohol oxygen, weakening the carbon–oxygen bond.

32. Under identical conditions, the rate constants for benzyl bromide and bromoethane are and , respectively. At equal substrate and nucleophile concentrations, the benzyl bromide reaction is faster by a factor of:

33. Arrange the following events in the appropriate order for electrophilic chlorination of benzene.
P. The sigma complex loses a proton.
Q. Benzene pi electrons attack the electrophilic chlorinating species.
R. Anhydrous activates and polarises .
S. Aromaticity is restored and chlorobenzene is obtained.

34. Assess the following statements about ordinary addition of hydrogen halides to alkenes.
Statement I: The alkene pi bond is replaced by new carbon–hydrogen and carbon–halogen sigma bonds.
Statement II: Unsymmetrical alkenes commonly show orientation controlled by carbocation stability.
Statement III: The reaction always requires ultraviolet light to generate halogen radicals.

35. Methyl iodide, , is treated as a separate limiting case rather than as a primary haloalkane because:

36. A reaction mixture intended to contain propylmagnesium bromide is accidentally exposed to moist air. Analysis later detects propane and very little organomagnesium compound. The observation is best explained by:

37. Complete reaction of of butan--ol with excess produces:

38. A tetrahedral carbon atom becomes a stereogenic centre when it is bonded to:

39. Arrange the following stages in the correct order for preparing a carboxylic acid from an alkyl halide through a Grignard reagent.
P. The alkyl halide reacts with magnesium in dry ether.
Q. The Grignard reagent attacks carbon dioxide.
R. A magnesium carboxylate is formed.
S. Acidic hydrolysis gives the carboxylic acid.

40. Appraise the following statements.
Statement I: A chiral haloalkane may exist as two non-superimposable mirror images.
Statement II: Every secondary haloalkane is chiral.
Statement III: A tetrahedral carbon with two identical substituents is not a stereogenic centre.

41. Read the situation below and answer the question.
A student nitrates chlorobenzene and isolates two principal isomers. Isomer P has chlorine and the nitro group on adjacent ring carbons. Isomer Q has the two substituents opposite each other and is obtained in the larger amount.
The correct identification is:

42. The IUPAC name of is:

43. The haloalkane most suitable for preparing an ether efficiently by the Williamson method is generally:

44. Evaluate the following statements about carbocation stability and reactions.
Statement I: Benzylic and allylic carbocations can be stabilised by resonance.
Statement II: Ordinary primary haloalkanes are generally poor substrates.
Statement III: Methyl halides are usually the fastest ordinary substrates.

45. A facility uses a volatile chlorinated solvent and also handles a persistent organohalogen pesticide. Which management plan best addresses both immediate and long-term risks?

46. Inspect the following chloroform-storage measures.

The appropriate evaluation is:

47. Three haloalkanes contain the same alkyl group. Their relative molar masses and observed boiling-point positions follow the order

for both quantities.

What best explains this parallel trend?

48. A laboratory record gives the following condition–product assignments.

The row requiring correction is:

49. A learner uses instead of after preparing benzenediazonium chloride and claims that both reagents have the same role. The best correction is:

50. The expected boiling-point order for the three isomeric chlorobutanes listed below is:
P. -chlorobutane
Q. -chloro--methylpropane
R. -chloro--methylpropane