We already know that a methyl is an electron donor group thus hampering the resonance of nitrogen's electron lone-pair. A methylaniline should be therefore more basic than the unsubstituted aniline and thus display a lower pKb value. This is what clearly happens in para-methylaniline whose pKb was reduced by 0.5 units from aniline. On the other hand, the effect of the methyl group in meta is minimal and this is reasonable because the nitrogen's electron density delocalizes primarily on the ortho and para positions. However, the pKb value of the ortho-methylanilina is puzzling because is slightly higher, against our prediction. The slightly lower basicity of ortho-methylaniline has to be explained in terms of the steric hindrance imposed by the neighboring methyl group to the approach of the external acid.