CONICET | Buscador de Institutos y Recursos Humanos

Infrared spectra at 300 and 77 K and Raman spectra at 300 K of the valpromide (Vpd), N-substituted derivatives: Nethylvalpromide (Etvpd), N-sopropylvalpromide (Ipvpd) and the N,N-disubstituted derivative: N,N-dimethylvalpromide (Dmvpd) with antiepileptic activity have been measured and analyzed with results derived from computational chemistry calculation. In agreement with theoretical predictions, experimental data indicate that while in the Etvpd, Dmvpd and Ipvpd there are four different conformational co-existing components Etvpd: TTCG+, TCCG−, TTTC,G+G+CG+;Dmvpd: TTCC,G−TTA+,G+A−TC, G+A−C A+; Ipvpd: TTCT, TCCT, TCCC, G− TTT; in the Vpd there are only three distinct stable conformations of C1 symmetry group: TTC, TCT, G+G+T. Based on the accuracy of the B3LYP calculation,with the 6-31+G∗∗ basis set estimated by comparison between the predicted values of the vibrational modes and the available experimental data, we performed a structural and vibrational study of the amide group in the Vpd and their derivatives. We found that small nonplanarity deviations of C( O)N backbone induce significant changes on the structural and spectroscopic properties. These are not compatible with the decreasing of the resonance effect as it is produced when the twisting around the C( O)?N increases. From the Natural Bond Orbital (NBO) ?analysis the existence of stabilizing electrostatic interactions of type C?H· · ·O/N and C?H· · ·H?N/C which induce significant structural changes and a complex electronic redistribution of charge on the π-system in those structures becomes evident.We view this as a consequence of the filled electron density change Lewis-type NBOs type lpO1,2, lpN1, σ(C?H)N?acyl and empty non-Lewis NBOs type σ∗(C?H)N?acyl, σ∗(N?H.)

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