Hydrocarbons

NEET Chemistry · 53 questions · Page 3 of 6 · Click an option or "Show Solution" to reveal answer

Q21

Reaction of HBr with propene in the presence of peroxide gives

A isopropyl bromide

B 3-bromopropane

C allyl bromide

D n-propyl bromide

Correct Answer

Option D

Solution

Reaction of HBr with propene in the presence of peroxide gives n-propyl bromide.

This addition reaction is an example of anti-Markovnikov’s addition reaction.

Q22

Using anhydrous AlCl 3 as catalyst, which one of the following reactions produces ethylbenzene (PhEt)?

A H 3 C

-

CH 2 OH + C 6 H 6

B CH 3

-

=

CH 2 + C 6 H 6

C H 2 C

=

CH 2 + C 6 H 6

D H 3 C

-

CH 3 + C 6 H 6

Correct Answer

Option C

Solution

With ethene in presence of anhydrous AlCl3, benzene gives ethyl benzene (PhEt).

Q23

The correct order of reactivity towards the electrophilic substitution of the compounds aniline (I), benzene (II) and nitrobenzene (III) is

A III > II > I

B II > III > I

C I < II > III

D I > II > III

Correct Answer

Option D

Solution

–NH 2 group is electron donating hence increases electron density on ring.

Benzene is also electron rich due to delocalisation of electrons. –NO 2 group is electron withdrawing hence, decreases electron density on ring.

Thus, correct order for electrophilic substitution is I $>$ II $>$ III.

Q24

2-Butene shows geometrical isomerism due to

A restricted rotation about double bond

B free rotation about double bond

C free rotation about single bond

D chiral carbon

Correct Answer

Option A

Solution

Due to restricted rotation about double bond, 2-butene shows geometrical isomerism.

Q25

Which reagent converts propene to 1-propanol ?

A H 2 O, H 2 SO 4

B B 2 H 6 , H 2 O 2 , OH

-

C Hg(OAc) 2 , NaBH 4 /H 2 O

D Aq. KOH

Correct Answer

Option B

Solution

Propene adds to diborane (B 2 H 6 ) giving an addition product.

The addition compound on oxidation gives 1-propanol.

Here addition of water takes place according to anti-Markownikoff’s rule.

Q26

Which is maximum stable?

A 1-Butene

B cis-2-Butene

C trans-2-Butene

D All have same stability.

Correct Answer

Option C

Solution

This is most stable as the repulsion between two methyl groups is least.

Q27

Increasing order of electrophilic substitution for following compounds

A IV < I < II < III

B III < II < I < IV

C I < IV < III < II

D II < III < I < IV

Correct Answer

Option A

Solution

Among —CH 3 , —OCH 3 and CF 3 , CH 3 and —OCH 3 are electron donating groups.

Hence, they activate the benzene ring.

In these the order of activation is —OCH 3 $>$ —CH 3 while —CF 3 group deactivates the benzene nucleus.

So, it shows lower rate of electrophilic substitution on benzene ring.

Thus, order of electrophilic substitution is :

Q28

Dihedral angle in staggered form of ethane is

A 0 o

B 12 o

C 60 o

D 180 o

Correct Answer

Option C

Solution

The staggered form of ethane has the following structure and the dihedral angle is 60 o , which means ‘H’ atoms are at an angle of 60 o to each other.

Q29

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.

Q30

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

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