Quantum semiempirical studies on the formation of aromatic polyamides, 1. Effect of structural parameters of diamines on the polyamidation reaction

A semiempirical quantum‐mechanical study of structural and electronic parameters of aromatic diamines was performed using the method AM1. The diamines have been considered as condensation monomers, and the reactivities of both amino groups against acyl chlorides have been computed. The study shows that the amidation reaction is controlled mainly by the global charge on the amino group and, in a much smaller extent, by the frontier orbitals. This behaviour is consistent with the large energy gap between the HOMO 1 HOMO: highest occupied molecular orbital. of the diamine and the LUMO 2 LUMO: lowest unoccupied molecular orbital. of the acyl chloride. It has been found also that the electronic nature of the substituents, affecting the charge of the amino groups, greatly affects the carbons directly joined to these groups. This permits to correlate the reactivities with the calculated charges on these carbons: