Engineering Chemistry S Datta

182 ENGINEERING CHEMISTRY
Q. 42. What do you mean by steric inhibition of resonance?
Ans. 2, 6-Dimethyl –N, N-dimethyl aniline (I) is more basic than N, N-dimethylaniline
(II). Due to crowding in (I), —N(Me) 2
group goes out of plane of the benzene ring by free
rotation about the single bond. So primary condition of resonance, the planarity, is affected
and resonance is inhibited. So lone pair over —N(Me) 2
group in (I) is available to be accepted
by a proton (H + ). This is an example of steric inhibition of resonance. But in (II) lone pair over
—N(Me) 2
comes into resonance with benzene ring and not so much available for an H + .
HC 3
CH 3
N
HC 3
CH 3
:
N
:
CH3 CH3
(I)
Q. 43. When Phenol is treated with NaNO 2
and HCl at 0–5°C, p-nitrosophenol is
obtained. Is this reaction an electrophilic substitution?
Ans. Yes, here the electrophile is NO +
(II)
HONO + HCl
NOCl + H O 2
+
NO+Cl –
OH
OH
+ OH
+NO
+ NO H
+H +
NO
EXERCISES
1. Classify the different organic reactions.
2. What do you mean by polarisation? What is the reason behind it?
3. What do you mean by inductive effect? How does it play an important role in organic reactions?
4. Compare the acidity among
CH 3
COOH, CH 2
Cl.COOH, CH.Cl 2
COOH, CCl 3
COOH.
5. What is electromeric effect? Is it permanent?
6. State the origin of a carbocation, carbonium ion and free radical.
7. State the products obtained during the chlorination of CH 4
in diffused sunlight. Mention the
mechanism.
8. What is polymerisation reaction? Give an example of such type of reaction with plausible mechanism.
9. What do you mean by electrophiles and nucleophiles?