MCQ
Its basic strength is $10^{10}$ more than $I$ -dimethyl amino naphthalene. Reason for high basic strength is
- Aresonance
- ✓steric inhibitation of resonance
- Cortho effect
- Dhyperconjugation
✓
Answer
Correct option: B.
steric inhibitation of resonance
b
$(b)$ Steric effects can indirectly affect acidity or basicity by affecting the resonance. Steric effects can also be caused by other types of strain. $1,8$ - bis(diethylamino)- $2, 7$ -dimethoxynaphthalene $(1) $ is an extremely strong base for a tertiary amine ($pK_a$ of the conjugate acid $= 16.3$; compare $N, N$ - dimethylaniline , $pK_a = 5.1$), but proton transfers to and from the nitrogen are exceptionaly slow ; enough to be followed by a $uv$ -spectrophotometer. $1$ is severely strained because the two nitrogen lorie pairs are forced to be near each other. Protonation relieves the strain : one lone pair is now connected to a hydrogen, which forms a hydrogen bond to the other lone pair (shown in $2$). The same effects are found in $4, 5$ -bis (dimethylamino) fluorene $(3)$ and $4$, $5$ - bis (dimethylamino).
$(b)$ Steric effects can indirectly affect acidity or basicity by affecting the resonance. Steric effects can also be caused by other types of strain. $1,8$ - bis(diethylamino)- $2, 7$ -dimethoxynaphthalene $(1) $ is an extremely strong base for a tertiary amine ($pK_a$ of the conjugate acid $= 16.3$; compare $N, N$ - dimethylaniline , $pK_a = 5.1$), but proton transfers to and from the nitrogen are exceptionaly slow ; enough to be followed by a $uv$ -spectrophotometer. $1$ is severely strained because the two nitrogen lorie pairs are forced to be near each other. Protonation relieves the strain : one lone pair is now connected to a hydrogen, which forms a hydrogen bond to the other lone pair (shown in $2$). The same effects are found in $4, 5$ -bis (dimethylamino) fluorene $(3)$ and $4$, $5$ - bis (dimethylamino).
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