A complete analysis of the transverse acoustic modes ( TAMs) for the homologous series of alpha,omega-diamines ( H2N( CH2)(n)NH2) ( n = 2-10, n = 12) as well as for the biogenic polyamines spermidine and spermine was undertaken, by Raman and inelastic neutron scattering ( INS) spectroscopies combined with density functional theory ( DFT) calculations. A complete assignment of the whole set of TAMs was carried out, for both the undeuterated and N-deuterated species. 1,2-Diaminoethane was found to display exceptional behavior, probably due to the formation of dimers in the solid state. An n-even/n-odd dependence of the low frequency INS pattern was observed for these polyamines. The very good accordance between their INS experimental TAMs and the ones previously reported for the corresponding n-alkanes suggest a close conformational similarity between these systems.