CONFORMATIONS AND INFRARED-SPECTRA OF ALPHA-OXO KETENES FROM AB-INITIO CALCULATIONS - THE ROLE OF ELECTROSTATICS

被引:47
作者
BIRNEY, DM
机构
[1] Department of Chemistry and Biochemistry, Texas Tech University, Lubbock
关键词
D O I
10.1021/jo00088a043
中图分类号
O62 [有机化学];
学科分类号
070303 ; 081704 ;
摘要
The Z and E conformations of acetylketene (3) and its 2-methyl- and 2-chloro derivatives (6 and 8, respectively) have been obtained using ab initio molecular orbital theory at the RHF/6-31G* level, while formylketene (12) was studied at the MP2/6-31G* level. Comparison of the calculated IR spectra (RHF/6-31G*) with the experimental spectra aids in the assignment of observed absorptions, provides an estimate of the Z/E ratio, and offers an explanation of trends in the IR spectre. The relative energies were calculated at the MP2 through MP4(SDQ)/6-31G* levels, all of which predict that the Z conformations of 3 and 8 are more stable, while the E conformation of 6 is favored, in quantitative agreement with experiment. The underlying preference for the Z conformation is due to an electrostatic attraction between the carbonyl oxygen and the central carbon of the ketene. However, steric and entropic effects combine to make E the preferred conformation of 6.
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页码:2557 / 2564
页数:8
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