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16
MCQ (Multiple Correct Answer)

In an electrophilic substitution reaction of nitrobenzene, the presence of nitro group ......... .

A
deactivates the ring by inductive effect
B
activates the ring by inductive effect
C
decreases the charge density at ortho and para position of the ring relative to meta position by resonance
D
increases the charge density at meta position relative to the ortho and para positions of the ring by resonance
17
MCQ (Multiple Correct Answer)

Which of the following are correct?

A
$\mathrm{CH}_3-\mathrm{O}-\mathrm{CH}_2^{\oplus}$ is more stable than $\mathrm{CH}_3-\mathrm{CH}_2^{\oplus}$
B
$\left(\mathrm{CH}_3\right)_2 \mathrm{CH}^{\oplus}$ is less stable than $\mathrm{CH}_3-\mathrm{CH}_2-\mathrm{CH}_2^{\oplus}$
C
$\mathrm{CH}_2=\mathrm{CH}-\mathrm{CH}_2^{\oplus}$ is more stable than $\mathrm{CH}_3-\mathrm{CH}_2-\mathrm{CH}_2^{\oplus}$
D
$\mathrm{CH}_2=\mathrm{CH}^{\oplus}$ is more stable than $\mathrm{CH}_3-\mathrm{CH}_2^{\oplus}$
18
MCQ (Multiple Correct Answer)

Four structures are given in options (a) to (d). Examine them and select the aromatic structures.

A
B
C
D
19
MCQ (Multiple Correct Answer)

The molecules having dipole moment are ............. .

A
2,2-Dimethylpropane
B
trans-Pent-2-ene
C
cis-Hex-3-ene
D
2, 2, 3, 3 - Tetramethylbutane
20
Subjective

Why do alkenes prefer to undergo electrophilic addition reaction while arenes prefer electrophilic substitution reactions? Explain.

Explanation

Alkenes are rich source of loosely held pi $(\pi)$ electrons, due to which they show electrophilic addition reaction. Electrophilic addition reaction of alkenes are accompanied by large energy changes so these are energetically favourable than that of electrophilic substitution reactions. In special conditions alkenes also undergo free radical substitution reactions.

In arenes during electrophilic addition reactions, aromatic character of benzene ring is destroyed while during electrophilic substitution reaction it remains intact. Electrophilic substitution reactions of arenes are energetically more favourable than that of electrophilic addition reaction.

That's why alkenes prefer to undergo electrophilic addition reaction while arenes prefer electrophilic substitution reaction.

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