Structure and vibrational assignment of 3,4-diacetyl-2,5-hexanedione. A density functional theoretical study

Conformational analysis, tautomerization, IR, Raman, and NMR studies of 3-phenylazo-2,4-pentanedione

“…For the skeletal modes, the differences between the experimental and calculated frequencies are much smaller than those for N-H and C-H stretching frequencies. Similar discrepancies between the calculated and experimental frequencies have been noted in b-diketones [17,18,[22][23][24][25][26][27][28] and ketoamines [16]. The overestimation of the computed wavenumbers is quite systematic and can be corrected by applying appropriate scaling factors or scaling equations [28][29][30][31][32].…”

“…Upon deuteration, this band disappears and a new band with medium intensity appears at 1084 cm À1 . The NH and ND in-plane bending frequency in PAPD frequency is comparable with the OH and OD in-plane mode of the enol form of b-diketones, which occur in the 1247-1332 and 1041-1127 cm À1 ranges, respectively [17,18,[22][23][24][25][26][27].…”

“…Upon deuteration this band disappears and a new band appears at about 2310 cm À1 . Comparing with the OH stretching of the enol form of b-diketones, which their HWHH are several hundred cm À1 [17,18,[21][22][23][24][25][26], the N-H stretching in PAPZ is considerably sharp. Therefore, it is easily concluded that the hydrazo species (HA1) is predominant in the sample and there is no sign of azo-enol forms in the IR spectra.…”

“…Three bands at 3008, 2978, and 2960 cm À1 , compared with corresponding bands in AA and related compounds [21,22,[25][26][27], are assigned to the CH stretching modes of CH 3 groups.…”

Physicochemical studies of molecular hyperpolarizability of imidazole derivatives

“…The intramolecular interactions are formed by the orbital overlap between (C-C) and *(C-C) bond orbital which results intramolecular charge transfer (ICT) causing stabilization of the system. These interactions are observed as increase in electron density (ED) in C-C antibonding orbital that weakens the respective bonds [27].…”