A THEORETICAL STUDY OF KETO-ENOL ISOMERISM AND INTERNAL ROTATION IN THE H(2)Salen MOLECULE, N,N '-ETHYLENE-BIS(SALICYLIDENIMINE)-SCHIFF BASE

作者：Sliznev V V^*; Girichev G V

来源：Journal of Structural Chemistry, 2011, 52(1): 16-26.

• Schiff base
• H(2)Salen
• structure
• keto-enol isomerism
• internal rotation
• conformers
• intramolecular hydrogen bond
• hyperconjugation
• electron density functional theory

Geometric parameters, vibrational spectra, and the energies of isomerization of seven keto-enol isomeric forms of the H(2)Salen molecule (N,N'-ethylene-bis(salicylidenimine)) are calculated using electron density functional theory (DFT/B3LYP) and correlation consistent valence triple-zeta Gaussian basis sets (cc-pvtz). The isomer with two enol groups (EE1) and C-2 symmetry configuration is most energetically favorable. Calculations of the keto-enol equilibrium show that at T >= 250 K the H(2)Salen gas phase is a mixture of four conformers (rotamers of the main isomer EE1). The contribution of other isomers does not exceed a few percent. The NBO analysis reveals that the system of p-conjugated bonds involves not only the atoms of the benzene moiety, but also the O, C, and N atoms nearest to the benzene ring. The energy stabilization of the isomer EE1 is shown to be due to the presence of two strong intramolecular N center dot center dot center dot H hydrogen bonds. Intramolecular N center dot center dot center dot H and O center dot center dot center dot H hydrogen bonds are observed in all other isomers. The bathochromic shift of O-H and N-H vibrational frequencies, caused by the effect of hydrogen bonds, is 520-790 cm(-1).

• 出版日期2011-2