Vibrational frequencies and structural determinations of hexamethylenetetraamine

The normal mode frequencies and corresponding vibrational assignments of hexamethylenetetraamine (HMTA) in Td symmetry are examined theoretically using the Gaussian 98 set of quantum chemistry codes. All normal modes were successfully assigned to one of eight types of motion predicted by a group theoretical analysis. The vibrational modes of the deuterated form of HMTA (HMTA d-12) were also calculated and compared against experimental data. The normal mode vibrational frequencies were shifted to lower frequencies as on deuteration as expected. However, in some cases the dominant motion type changed on deuteration leading to an apparent 'blue shift' of some of the N-C stretching modes. It is possible that the observed frequency shifts are the result of a Fermi resonance condition.