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

Question 1. When

P h - O H

reacts with

C_{2} H_{5} I

with anhydrous

C_{2} H_{5} O H

as the solvent in the presence of ethoxide ions, what is the product of this reaction?

Ph−Me
Ph−O−Me
Ph−O−Et
Ph−Et

Explanation:-

Answer: Option C. -> Ph−O−Et
:
C
Watch the video that follows!

Question 2. Consider the following reactions carried out at the same temperature:

C H_{3} B r + O H^{-} C_{2} H_{5} O H - ---- \to C H_{3} O H + B r^{-}

C H_{3} B r + O H^{-} (C H_{3})_{2} S O - ----- \to C H_{3} O H + B r^{-}

Which of the following statements is correct about these reactions?

The first reaction occurs faster than the second
The second reaction occurs faster than the first
Both the reactions occurs at the same rate
Addition of NaI has no effect no either of these reactions

Explanation:-

Answer: Option B. -> The second reaction occurs faster than the first
:
B
Polar aprotic solvents such as DMSO increase the rate of the

S_{N} 2

reaction.

Question 3. 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 4. Rate of Reaction,

is fastest when ‘Z’ is

OC2H5
NH2
Cl
OCOCH3

Explanation:-

Answer: Option C. -> Cl
:
C
Acid halides react fastest among acid derivates.

Question 5. The major product formed in the following reaction is :

Explanation:-

Answer: Option C. -> Cl
:
C
In protic solvent

E_{2}

proceeds over

S_{N} 2

.

Question 6. A solution containing 0.2563 g of naphthalene (molecular mass = 128) in 50 g of carbon tetrachloride yields a boiling point elevation of

{0.201}^{\circ} C

while a solution of 0.6216 g of an unknown solute in the same mass of the solvent gives a boiling point elevation of

{0.647}^{\circ} C

. Find the molecular mass of unknown solute.

96.44
86.44
90
88

Explanation:-

Answer: Option A. -> 96.44
:
A
We know that

K_{b} = \frac{Δ T_{b} \times W_{1} \times M w_{2}}{1000 \times W_{2}}

First let’s calculate value of

K_{b} f o r C C l_{4}

.
For

C C l_{4};

K_{b} = \frac{0.201 \times 50 \times 128}{1000 \times 0.2563} = 5.019 k k g m o l^{- 1}

Now, for calculating mass of unknown solute, we can use the same value of

K_{b}

.

M w_{2} = \frac{1000 \times K_{b} \times W_{2}}{Δ T_{b} \times W_{1}}

\frac{1000 \times 5.019 \times 0.6216}{0.647 \times 50}

= 96.44

Question 7. What is the order of reactivity of the following compounds towards nucleophilic substitution?

IV
IV
III
II

Explanation:-

Answer: Option B. -> IV
:
B
The reactivity depends on the stability of the carbocation obtained upon ionization. Theorder of stability is .

Question 8.

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 9. The product in the following reaction is

Explanation:-

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

Question 10.

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.