Molecular structure and relative stability of trans and cis isomers of formanilide: gas-phase electron diffraction and quantum chemical studies

被引:5
作者
Marochkin, Ilya I. [1 ]
Dorofeeva, Olga V. [1 ]
机构
[1] Moscow MV Lomonosov State Univ, Dept Chem, Moscow 119991, Russia
关键词
Formanilide; Molecular structure; Isomers; Gas-phase electron diffraction; Ab initio and DFT calculations; Bond energy; ZEKE PHOTOELECTRON-SPECTROSCOPY; N-PHENYL FORMAMIDE; AB-INITIO; ROTATIONAL SPECTRUM; HYDRATED CLUSTERS; BOND; PHENYLFORMAMIDE; THERMOCHEMISTRY; ENTHALPIES; BENZAMIDE;
D O I
10.1007/s11224-012-0071-6
中图分类号
O6 [化学];
学科分类号
0703 ;
摘要
Molecular structure of formanilide is determined by gas-phase electron diffraction (GED) augmented by quantum chemical calculations (B3LYP/cc-pVTZ and MP2/cc-pVTZ) and literature microwave (MW) data. The combined GED and MW data are well reproduced for the mixture of trans and cis isomers with the relative abundance of 59 +/- A 5 and 41 +/- A 5 %, respectively, at T = 410 K. The trans isomer (C (s) symmetry) is planar, while the cis isomer (C (1) symmetry) has the twisted structure with the amide group rotated by 36.7 +/- A 2.7A degrees with respect to the phenyl ring. In accord with theoretical calculations, the amide bond -NH-C(O)- is planar in trans formanilide and a somewhat nonplanar in cis isomer. Accurate structural parameters were obtained by a simultaneous fit of the rotational constants reported in the literature and GED intensities obtained in this study. The N-C(O) and N-C-Ph bond dissociation energies in formanilide are calculated using Gaussian-4 method. It is revealed that the strength of N-C(O) bond in formanilide is 50 kJ/mol less than that in benzamide. On the contrary, the strength of adjacent bond (N-C-Ph) increases by 35 kJ/mol compared to aniline. It is rather unexpectedly that the bond strength weakening does not result in the bond elongating, and vice versa.
引用
收藏
页码:233 / 242
页数:10
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