THE INFLUENCE OF STERIC AND ORBITAL INTEREACTIONS ON MOLECULAR STRUCTURE IN N-SUBSTITUTED PIPERIDINES

DOI: 10.6060/tcct.20165911.5464
Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2016. V. 59. N 11. P. 19-26

The conformational behavior and molecular structures of several N-substituted piper-idines containing heteroatoms of the Va and VIa subgroups were studied by quantum chemi-cal (QC) calculations (RnX-piperidines, R=H or CH3; n=1: X=O or S; n=2: X=N or P). These compounds may exist as three or four conformers differing by axial and/or equatorial posi-tions and gauche and trans or cis and trans orientation of the substituent relative to the piper-idine ring. The axial/equatorial preference is strongly influenced by the 1,3-diaxial interac-tion, while mostly the orbital interaction governs the gauche, cis and trans orientation of the substituent. The gauche-equatorial conformers are more stable than other forms in case of R2X-piperidines, but the trans-equatorial form is most stable in the RO-, and cis-equatorial – in the RS-piperidines. The energy barrier for nitrogen inversion increases in the series P→S→N→O.

Key words: N-substituted piperidine, quantum chemical calculation, conformational properties, orbital interaction, steric repulsion

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2016, Т. 59, № 11, Стр. 19-26