Second ortho effect: ortho effect in substituted aniline (steric inhibition of protonation) When any group is present at ortho to NH2 in aniline then the basic character of that compound becomes at least less than aniline. For example see the order of basicity of following substituted aniline:- p-Toluidine > m-Toluidine > Aniline > o-Toluidine Aniline > m-Nitroaniline > p-Nitroaniline > o-Nitroaniline Aniline > p-Haloaniline > m-Haloaniline > o-Haloaniline p-Aminophenol  > Aniline > o-Aminophenol  >  m-Aminophenol 
Second ortho effect: ortho effect in substituted aniline (steric inhibition of protonation) When any group is present at ortho to NH2 in aniline then the basic character of that compound becomes at least less than aniline. For example see the order of basicity of following substituted aniline:- p-Toluidine > m-Toluidine > Aniline > o-Toluidine Aniline > m-Nitroaniline > p-Nitroaniline > o-Nitroaniline Aniline > p-Haloaniline > m-Haloaniline > o-Haloaniline p-Aminophenol pKb=8.50 > o-Aminophenol pKb=9.28 > Aniline pKb=9.38 > m-Aminophenol pKb=9.80
A
pKb=8.50
D
Aniline >
A
pKb=9.28
A
Aniline pKb=9.38 >
A
pKb=9.80