Haloalkanes and Haloarenes — CBSE Class 12 board PYQs

Auto-oxidation of chloroform in air and light produces a poisonous gas known as:

Assertion (A): Inversion of configuration is observed in the S${}_{\mathrm{N}}$2 reaction.
Reason (R): The reaction proceeds with the formation of a carbocation.

The substitution reaction of an alkyl halide mainly occurs by the SN1 or SN2 mechanism. Whatever mechanism alkyl halides follow for the substitution reaction to occur, the polarity of the carbon-halogen bond is responsible for these substitution reactions. The rate of SN1 reactio …

The substitution reaction of an alkyl halide mainly occurs by the SN1 or SN2 mechanism. Whatever mechanism alkyl halides follow for the substitution reaction to occur, the polarity of the carbon-halogen bond is responsible for these substitution reactions. The rate of SN1 reactio …

The substitution reaction of an alkyl halide mainly occurs by the SN1 or SN2 mechanism. Whatever mechanism alkyl halides follow for the substitution reaction to occur, the polarity of the carbon-halogen bond is responsible for these substitution reactions. The rate of SN1 reactio …

Define ambident nucleophile, with an example.

Out of chlorobenzene and benzyl chloride, which one gets easily hydrolysed by aqueous NaOH, and why?

Of the two halides shown in the figure (3-halocyclohex-1-ene and 1-halocyclohex-1-ene), which is an example of an allylic halide?

Which of the two reactions shown in the figure is S${}_{\mathrm{N}}$2, and why?

Of the two chlorides shown in the figure (2-chlorobutane and 1-chloro-2-methylpropane), which is more reactive towards the S${}_{\mathrm{N}}$1 reaction, and why?

Which of the two compounds shown in the figure (CH${}_3$CH${}_2$Br and (CH${}_3$)${}_3$CBr) would undergo the S${}_{\mathrm{N}}$2 reaction faster, and why?

Write the IUPAC name of the following compound:
CH${}_2$=CH–CH${}_2$Br

Write the IUPAC name of the following compound:
(CH${}_3$)${}_3$C–CH${}_2$Br

Write the structure of the following compound:
1,4-Dibromobut-2-ene

Give the IUPAC name of the following compound (structure shown in the figure).

Account for the following:
(a) Haloalkanes react with AgCN to form isocyanides as the main product.
(b) Allyl chloride shows high reactivity towards the S${}_{\mathrm{N}}$1 reaction.
(c) Haloarenes are extremely less reactive towards nucleophilic substitution reactions.

Write equations for the following:
a) oxidation of chloroform by air and light
b) reaction of chlorobenzene with CH${}_3$Cl / anhydrous AlCl${}_3$

The following compounds are given to you:
2-bromopentane, 2-bromo-2-methylbutane, 1-bromopentane
(a) Write the compound which is most reactive towards the S${}_{\mathrm{N}}$2 reaction.
(b) Write the compound which is optically active.
(c) Write the compound which is most reactive tow …

(a) Identify the chiral molecule in the pair shown in the figure (3-methylbutan-2-ol and 2,4-dimethylpentan-3-ol).
(b) Write the structure of the product when chlorobenzene is treated with methyl chloride in the presence of sodium metal and dry ether.
(c) Write the structure of t …

Write the major monohalo product(s) in each of the reactions shown in the figure (three substrate + reagent pairs, labelled i, ii and iv as printed).

Give reasons:
i) The C–Cl bond length in chlorobenzene is shorter than the C–Cl bond length in CH${}_3$–Cl.
ii) The dipole moment of chlorobenzene is lower than that of cyclohexyl chloride.
iii) S${}_{\mathrm{N}}$1 reactions are accompanied by racemisation in optically active alkyl hal …

Give reasons:
a) n-Butyl bromide has a higher boiling point than t-butyl bromide.
b) A racemic mixture is optically inactive.
c) The presence of a nitro group (–NO${}_2$) at the o/p positions increases the reactivity of haloarenes towards nucleophilic substitution reactions.

Answer the following:
i) Haloalkanes easily dissolve in organic solvents. Why?
ii) What is a racemic mixture? Give an example.
iii) Of the two bromo derivatives, C${}_6$H${}_5$CH(CH${}_3$)Br and C${}_6$H${}_5$CH(C${}_6$H${}_5$)Br, which one is more reactive towards the S${}_{\mathrm{N}}$1 substitu …

Rearrange the compounds of each of the following sets in order of reactivity towards S${}_{\mathrm{N}}$2 displacement:
i) 2-bromo-2-methylbutane, 1-bromopentane, 2-bromopentane
ii) 1-bromo-3-methylbutane, 2-bromo-2-methylbutane, 2-bromo-3-methylbutane
iii) 1-bromobutane, 1-bromo-2,2- …

How would you differentiate between the S${}_{\mathrm{N}}$1 and S${}_{\mathrm{N}}$2 mechanisms of substitution reactions? Give one example of each.

i) State one use each of DDT and iodoform.
ii) Which compound in the following couples will react faster in S${}_{\mathrm{N}}$2 displacement, and why?
a) 1-bromopentane or 2-bromopentane
b) 1-bromo-2-methylbutane or 2-bromo-2-methylbutane

How are the following conversions carried out?
i) benzyl chloride to benzyl alcohol
ii) methyl magnesium bromide to 2-methylpropan-2-ol

Which one of each of the following pairs (shown in the figure) undergoes the S${}_{\mathrm{N}}$1 substitution reaction faster, and why?
i) 2-chloro-2-methylpropane or 2-chloropentane
ii) 3-chlorohexane or 1-chloropentane

Complete the following reaction equations (as shown in the figure):
i) CH${}_3$CH${}_2$CH${}_2$OH + SOCl${}_2$ →
ii) CH${}_3$CH${}_2$CH=CH${}_2$ + HBr (peroxide) →

Which one in each of the following pairs of substances (shown in the figure) undergoes the S${}_{\mathrm{N}}$2 substitution reaction faster, and why?
i) (chloromethyl)cyclohexane or chlorocyclohexane
ii) 1-iodopentane or 1-chloropentane

i) Why are haloalkanes more reactive than haloarenes towards nucleophilic substitution reactions?
ii) Which of the two substances shown in the figure (3-chloropentane and 1-chloropentane) undergoes the S${}_{\mathrm{N}}$1 reaction faster, and why?

Explain why haloarenes are much less reactive than haloalkanes towards nucleophilic substitution reactions.
OR
Which compound in each of the following pairs will react faster in an S${}_{\mathrm{N}}$2 reaction with OH⁻? Why?
i) CH${}_3$Br or CH${}_3$I
ii) (CH${}_3$)${}_3$CCl or CH${}_3$Cl

a) Which one of the two compounds, CH${}_3$Br and CH${}_3$I, will react faster in an S${}_{\mathrm{N}}$2 reaction with OH⁻?
b) Write the structures of the major products in the following reactions:
i) CH${}_3$CH=C(CH${}_3$)${}_2$ + HBr →
ii) C${}_6$H${}_5$ONa + C${}_2$H${}_5$Cl →

How may methyl bromide be preferentially converted to methyl cyanide and to methyl isocyanide?

(i) Out of (CH${}_3$)${}_3$C–Br and (CH${}_3$)${}_3$C–I, which one is more reactive towards S${}_{\mathrm{N}}$1, and why?
(ii) Write the product formed when p-nitrochlorobenzene is heated with aqueous NaOH at 443 K, followed by acidification.
(iii) Why are the dextro- and laevo-rotatory isom …

Nucleophilic substitution of a haloalkane can proceed by either the SN1 or the SN2 mechanism. SN1 is a two-step reaction while SN2 is a single-step reaction; which mechanism a haloalkane follows depends on the structure of the haloalkane, the leaving group, the nucleophile and th …