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).