On the electron density topology and electrostatic properties of nitroanilines. A theoretical investigation on m-nitroaniline and 2-methyl-5-nitroaniline crystals.

On the basis of the AIM theory, intermolecular interactions have been characterized in the B3LYP/6-31G** periodic electron density of the title compounds. Although the set of bond paths identified in each system is not fully equivalent to its experimental counterpart, agreement is reasonable with regard to the nature and relative importance of the intermolecular interactions at play. Within the AIM partition scheme, the molecular dipole moment of the in-crystal molecule was determined for the title compounds and the two closely related crystals of 2-methyl-4-nitroaniline and p-nitroaniline. Using a method that relies only on molecular calculations and a mean electric field approximation, it was possible to reproduce within 6% the values of the molecular dipole moment modulus obtained directly from the periodic electron densities. This result reveals that, for this kind of molecular crystal, enhancement of the dipole moment in going from the isolated molecule to the in-crystal one is an almost exclusively inductive effect.