In 2,4,6-trinitro-N, N-dimethylaniline, the bulky nitro substituents at o-position throw the p-orbital of N-atom containing the lone pair of electrons out of the plane of the p-orbitals of the benzene ring. As a result delocalisation of nitrogen electrons on the ring cannot occur. In other words, these electrons are readily available for protonation and hence, it is much stronger base than 2,4 , 6-trinitroaniline, aniline and N,N-dimethylaniline where delocalisation is not inhibited by resonance.