Reaction Mechanism(11th And 12th > Chemistry ) Questions and answers for exam Preparation

Question 1.

Which of the following statements is incorrect for low reactivity of chloro benzene

Due to resonance
Polarity of C-X bond
sp² hybridised state of C atom
Due to +E effect of Cl

Explanation:-

Answer: Option D. -> Due to +E effect of Cl
:
D

Cl is involved in resonance as well as inductive effect and not in electrometric effect as it is more electronegative.

Question 2.

The product in the following reaction is

Explanation:-

Answer: Option A. ->

:
A

Question 3.

I > II > III
II > I > III
II > III > I
III > II > I

Explanation:-

Answer: Option C. -> II > III > I
:
C
The reactivity decreases in the order

Allylic > Secondary > primary.

Question 4.

The reagent for the above conversion is

Alcoholic KOH
Alcoholic KOH followed by NaNH₂
Aqueous KOH followed by NaNH₂
Zn/ CH₃COOH

Explanation:-

Answer: Option B. -> Alcoholic KOH followed by NaNH₂
:
B

Question 5.

What is the order of reactivity of the following compounds towards nucleophilic substitution?

$I V < I I I < I I < I$
$I V < I < I I < I I I$
$I I I < I V < I I < I$
$I I < I V < I I I < I$

Explanation:-

Answer: Option B. ->

I V < I < I I < I I I

:
B

The reactivity depends on the stability of the carbocation obtained upon ionization. The order of stability is .

Question 6.

The major product formed in the following reaction is :

Explanation:-

Answer: Option C. ->

:
C

In protic solvent $E_{2}$ proceeds over $S_{N} 2$ .

Question 7.

The structure of the major product formed in the following reaction is

Explanation:-

Answer: Option D. ->

:
D

Alkyl halides are more reactive than aryl halides, therefore the halogen present on the side chain is displaced.

Question 8.

Explanation:-

Answer: Option D. ->

:
D

Question 9.

The order of decreasing nucleophilicity is

$H_{2} O > O H^{-} > C H_{3} C O O^{-} > C H_{3} O^{-}$
$C H_{3} C O O^{-} > C H_{3} O^{-} > H O^{-} > H_{2} O$
$H O^{-} > C H_{3} O^{-} > C H_{3} C O O^{-} > H_{2} O$
$C H_{3} O^{-} > O H^{-} > C H_{3} C O O^{-} > H_{2} O$

Explanation:-

Answer: Option D. ->

C H_{3} O^{-} > O H^{-} > C H_{3} C O O^{-} > H_{2} O

:
D

1. Due to the presence of -ve charge $C H_{3} O^{-}$ , $O H^{-}, C H_{3} C O O^{-}$ , are more nucleophilic than $H_{2} O$ . Further due to + I effect of the $C H_{3}$ group, $C H_{3} O^{-}$ is more nucleophilic than $O H^{-}$ .

2. $C H_{3} C O O^{-}$ has the -ve charge on oxygen stabilized by resonance and therefore its nucloephilicity is less than those of $C H_{3} O^{-}$ and $O H^{-}$ .

Question 10.

The rate of $S_{N} 2$ reaction is maximum when the solvent is

$C H_{3} O H$
$H_{2} O$
DMSO
Benzene

Explanation:-

Answer: Option C. -> DMSO
:
C

Polar aprotic solvents such as DMSO increase the rate of the $S_{N} 2$ reaction.