Hydrocarbons Questions — JEE Chemistry

Q1

Metallic sodium does not react normally with :

A gaseous ammonia

B But-2-yne

C Ethyne

D tert-butyl alcohol

Correct Answer

Option B

Solution

Metallic sodium does not react with 2-butyne because 2-butyne does not have acidic hydrogen.

Q2

Total number of sigma (σ) _______ and pi(π) ______ bonds respectively present in hex-1-en-4-yne are:

A 14 and 3

B 11 and 3

C 13 and 3

D 3 and 13

Correct Answer

Option C

Solution

The compound given is hex - 1 - en - 4 - yne Structure is a double bond has one $\pi$ bond and one sigma bond.

A triple bond has one $\sigma$ bond and two $\pi$ bonds.

So, the number of $\pi$ bonds $=1+2=3$ For sigma bonds, count all carbon $-$ carbon bonds and carbon $-$ hydrogen bonds except the $\pi$ bonds in double bond and triple bond.

The number of sigma bonds = 13 So, total number of bonds $\Rightarrow \sigma=13\quad \pi=3$ Answer : option (C) 13 and 3

Q3

Which of the following is Lindlar catalyst?

A Partially deactivated palladised charcoal

B Zinc chloride and HCl

C Sodium and Liquid NH3

D Cold dilute solution of KMnO4

Correct Answer

Option A

Solution

Lindlar's catalyst $\Rightarrow$ Pd/CaCO3 + (CH3COO)2 Pb + quinolene

Q4

Which of these will not react with acetylene ?

A NaOH

B ammonical AgNO3

C Na

D HCl

Correct Answer

Option A

Solution

Acetylene reacts with the other three as :

Q5

Which one of the following has the minimum boiling point?

A n-butane

B isobutane

C 1- butene

D 1- butyne

Correct Answer

Option B

Solution

NOTE : Among isomeric alkanes, the straight chain isomer has higher boiling point than the branched chain isomer.

The greater the branching of the chain, the lower is the boiling point.

Further due to the presence of $\pi$ electrons, these molecules are slightly polar and hence have higher boiling points than the corresponding alkanes.

Thus

B.pt.

follows the order alkynes

>

alkene

>

alkanes (straight chain) > branched chain alkanes.

Q6

2 methylbutane on reacting with bromine in the presence of sunlight gives mainly

A 1 – bromo -2 - methylbutane

B 2 – bromo -2 - methylbutane

C 2 – bromo -3 - methylbutane

D 1 – bromo -3 – methylbutane

Correct Answer

Option B

Solution

Ease of replacement of

H

-atom

{3^ \circ } > {2^ \circ } > {1^ \circ }.

Q7

Which types of isomerism is shown by 2,3-dichlorobutane?

A Diastereo

B Optical

C Geometric

D Structural

Correct Answer

Option B

Solution

2,3

-dichloro butane will exhibit optical isomerism due to the presence of two asymmetric carbon atom.

Q8

The reaction of toluene with Cl2 in presence of FeCl3 gives predominantly

A benzoyl chloride

B benzyl chloride

C o-and p-chlorotoluene

D m-chlorotoluene

Correct Answer

Option C

Solution

FeC{l_3}\,\,

is Lewis acid. In presence of

FeC{l_3}\,\,

side chain hydrogen atoms of toluene are substituted.

Q9

The hydrocarbon which can react with sodium in liquid ammonia is

A CH3CH2CH2C≡CCH2CH2CH3

B CH3CH2C≡CH

C CH3CH=CHCH3

D CH3CH2C≡CCH2CH3

Correct Answer

Option B

Solution

Alkynes having terminal

- C \equiv H

react with Na in liquid ammonia to yield

{H_2}

gas of the given compounds

C{H_3}C{H_2}C \equiv CH

can react with Na in liquid

N{H_3}

so the correct answer is

(b).

Q10

In the following sequence of reactions, the alkene affords the compound ‘B’ CH3 - CH = CH - CH3

\overset{{{O_3}}}\longrightarrow

A

\mathrel{\mathop{\kern0pt\longrightarrow} \limits_{Zn}^{H{}_2O}}

B The compound B is

A CH3CH2CHO

B CH3COCH3

C CH3CH2COCH3

D CH3CHO

Correct Answer

Option D

Solution

Completing the sequence of given reactions, Thus

'B'\,\,

is

\,\,C{H_3}CHO

Hence

(d)

is correct answer.