Steric effects can idirectly affect or basicity by affecting resonance . Steric effect can also be caused by other typesof strain. 1,8 (diethylamino )-2 ,7-dimethoxynahthalene (1) is an extermely strong base for a tertiary amine `(pK_(a)` of the conjugate acid =6.3, compare N, N-dimethylanilne , `pK_(a)=5.1`) but proton transfers to and form the nitrogen are exceptionaly slow , enough to be followed by a uv-spectrophotometer . 1 is severly strained because the two nitrogen lone apir are forced to be near each other. Protonation relieves the strain : one lone pair is now conncected to a hydrogen , which froms a huydrogen bond to the other lone pair (show in 2) . The same effects are found in 4,5- bis (dimethylamino) fluorene (3) and 4 , 5-bis (dimethylamino)
