Case Study Questions for Class 12 Chemistry Chapter 10 Haloalkanes and Haloarenes

There is Case Study Questions in class 12 Chemistry in session 2020-21. For the first time, the board has introduced the case study questions in the board exam. The first two questions in the board exam question paper will be based on Case Study and Assertion & Reason. The first question will have 5 MCQs out of which students will have to attempt any 4 questions. The second question will carry 5 Assertion & Reason type questions with the choice to attempt any four. Here are the questions based on case study.

Case Study Question 1:

Read the passage given below and answer the following questions:

Nucleophilic substitution reactions are of two types; substitution nucleophilic bimolecular (SN2) and substitution nucleophilic unimolecular (SN1) depending on molecules taking part in determining the rate of reaction. Reactivity of alkyl halide towards SN1 and SN2 reactions depends on various factors such as steric hindrance, stability of intermediate or transition state and polarity of solvent. SN2 reaction mechanism is favoured mostly by primary alkyl halide or transition state and polarity of solvent, SN2 reaction mechanism is favoured mostly by primary alkyl halide then secondary and then tertiary. This order is reversed in case of SN1 reactions.

The following questions are multiple choice question. Choose the most appropriate answer:

(i) Which of the following is most reactive towards nucleophilic substitution reaction?
(a) C6H5Cl
(b) CH2=CHCl
(c) ClCH2CH=CH2
(d) CH3CH=CHCl

(ii) Isopropyl chloride undergoes hydrolysis by
(a) SN1 mechanism
(b) SN2 mechanism
(c) SN1 and SN2 mechanism
(d) neither SN1 nor SN2 mechanism

(iii) The most reactive nucleophile among the following is
(a) CH3O-
(b) C6H5O-
(c) (CH3)2CHO-
(d) (CH3)3CO-

(iv) Tertiary alkyl halides are practically inert to substitution by SN2 mechanism because of
(a) insolubility
(b) instability
(c) inductive effect
(d) steric hindrance

OR

Which of the following is the correct order of decreasing SN2 reactivity?
(a) RCH2X > R2CHX > R3CX
(b) R3CX > R2CHX >RCH2X
(c) R2CHX >R3CX > RCH2X
(d) RCH2X >R3CX >R2CHX

Answers (i) (c) Allylic chlorides are most reactive.
(ii) c
(iii) a
(iv) d
or
(a) Larger the number of alkyl groups at alpha-carbon atom, more is the steric hindrance and hence lesser the reactivity towards SN2 mechanism.

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