Mesomeric effects, aniline

With substituents such as OH and OMe that have unshared electron pairs, an electron-donating, i.e. base-strengthening, mesomeric effect can be exerted from the o- and p-, but not from the m-position, with the result that the p-substituted aniline is a stronger base than the corresponding w-compound. The m-compound is a weaker base than aniline itself, due to the electron-withdrawing inductive effect exerted by the oxygen atom in each case. As so often, the effect of the o-substituent remains somewhat anomalous, due to direct interaction with the NH2 group by both steric and polar effects. The substituted anilines are found to have related pAa values as follows ... 

The photolysis of aniline at high temperatures results in N-H and C-N clea-vage, but at room temperature the major reaction is fluorescence. Below 2800 A some photodecomposition takes place the lifetime and dissociation probability of excited aniline molecules have been calculated Flash photolysis of aniline followed by kinetic mass spectroscopy failed to reveal the presence of dissociation products. Irradiation of halogen derivatives of aniline between 2480 and 2562 A produces halide ions in measurable yields . Positive mesomeric effects increase, and negative mesomeric effects decrease... 

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