NEET Previous Year Questions (2014-2024): Haloalkanes & Haloarenes | Chemistry Class 12 PDF Download

2024

Q1: The compound that will undergo S_N1 reaction with the fastest rate is 
(a)
(b)
(c)
(d)              (2024)
Ans: (d)
Reactivity towards ,S_N1 depends upon stability of carbocation.
Order of stability is

2023

Q1: The given compound    (2023)
is an example of ______.
(a) Benzylic halide
(b) Aryl halide
(c) Allylic halide
(d) Vinylic halide
Ans: C
α-carbon is sp³ carbon which is right next to    
This a-position is known as allylic position
Hence,  

 is allylic halide 

2021

Q1: The major product of the following chemical reaction is :    (NEET 2021)

(a)

(b)

(c)

(d)  
Ans: (d)
Addition of HBr to an alkene in presence of a peroxide (benzoyl peroxide [(C₆H₅CO)₂O₂] gives an anti Markownikoff’s product. Anti-Markownikoff’s rule states that hydrogen is added to a more substituted carbon atom of an unsymmetrical alkene.

Q2: The major product formed in dehydrohalogenation reaction of 2-Bromo pentane is Pent-2-ene.This product formation is based on-     (NEET 2021)
(a) Hofmann Rule
(b) Huckel's Rule
(c) Saytzeff's Rule
(d) Hund's Rule
Ans: (c)
Major product formed in dehydrohalogenation reaction of 2-bromopentane is pent-2-ene because according to Saytzeff's Rule, in dehydrohalogenation reactions, the preferred product is that alkene which has greater number of alkyl group(s) attached to the doubly bonded carbon atoms.

2020

Q1: Which of the following alkane cannot be made in good yield by Wurtz reaction?    (NEET 2020)
(a) n-Heptane
(b) n-Butane
(c) n-Hexane
(d) 2,3-Dimethylbutane
Ans: A
Wurtz reaction is used to prepare symmetrical alkanes like

Using Wurtz reaction, n-Heptane can not be produced in good production because it is unsymmetrical alkane.

Q2: Elimination reaction of 2-Bromo-pentane to form pent-2-ene is:    (NEET 2020)
(a) β-Elimination reaction
(b) Follows Zaitsev rule
(c) Dehydrohalogenation reaction
(d) Dehydration reaction
(a) (b), (c), (d)
(b) (a), (b), (d) 
(c) (a), (b), (c)
(d) (a), (c), (d)
Ans: (c)

Since β-hydrogen is abstracted it is β-elimination.
Since more substituted alkene is formed (stable and major product), it follows Zaitsev's rule or Saytzev's rule.
Since H and Br are removed, it is dehydrohalogenation.

2018

Q9. The compound C7H8 undergoes the following reactions :    (NEET 2018)

The product ‘C’ is

(a) m–bromotoluene
(b) o–bromotoluene
(c) 3–bromo–2,4,6–trichlorotoluene
(d) p–bromotoluene
Ans: (d)

2017

Q10. Identify A and predict the type of reaction    (NEET 2017)

(a)
(b)
(c)
(d)
Ans: (d)

m-Bromoanisole gives only the respective meta substituted aniline. This is a substitution reaction which goes by an elimination-addition pathway.

2016

Q1: Consider the reaction,                     (NEET 2016 Phase 2)
CH₃CH₂CH₂Br + NaCN $\to$ CH₃CH₂CH₂CN + NaBr
This reaction will be the fastest in
(a) ethanol
(b) methanol
(c) N, N' -dimethylformamide (DMF)
(d) Water
Ans: (c)
The reaction,
CH₃CH₂CH₂Br + NaCN $\to$ CH₃CH₂CH₂CN + NaBr
follows S_N2 mechanism which is favoured by polar aprotic solvent i.e., N, N'–dimethylformamide (DMF). 

2015

Q1: In an S_N1 reaction on chiral centers, there is                      (NEET / AIPMT 2015
(a) inversion more than retention leading to partial racemisation
(b) 100% retention
(c) 100% inversion
(d) 100% racemisation
Ans: (a)

• In case of optically active alkyl halides, S_N1 reaction is accompanied by racemisation. The carbocation formed in the slow step being sp2 hybridised is planar and attack of nucleophile may take place from either side resulting in a mixture of products, one having the same configuration and other having inverted configuration.
• The isomer corresponding to inversion is present in slight excess because S_N1 also depends upon the degree of shielding of the front side of the reacting carbon.

2014

Q1: Which of the following compounds will undergo racemisation when solution of KOH  hydrolyses?  (AIPMT 2014)

(a) (iii) and (iv)
(b) (i) and (iv)
(c) (iv)
(d) (ii) and (iv)
Ans: (c)
Out of the given four compounds only (iv) compound is chiral and hence only this compound will undergo racemisation.