Ab initio studies of structural features not easily amenable to experiment. 43. Basis set dependence of C-O single bonds and comment on the microwave substitution structure of methyl-ethyl-ether

by Klimkowski, Valentine Joseph; Siam, Khamis S.; Ewbank, John David; Schäfer, Lothar; Geise, Herman J.; Van Alsenoy, Christian

The geometries of CH3OCH, CH3OCH3, C2H5OH3, and ethylene oxide were refined by Pulay's ab initio gradient method (1969) on the 6-513 G** level, in order to comment on a previously noted irregularity in the differences between the 4-21G andrsC-O bond distances of C2H5OCH3and ethylene oxide. It is concluded that, in the case of ethylene oxide, the unusually large difference of 0.049 Aring between the 4.21G and thersC-O bond lengths is mainly due to deficiencies of the 4-21G basis in predicting the structures of strained cyclic organic systems containing hetero-atoms. In the case of C2H5OCH3, however, the most credible interpretation of the currently available data is that experimental uncertainties contribute significantly to the relatively large difference of 0.040 Aring between the 4-21G andrsC(methylene)-O bonds, and thersparameters very likely are not a true measure of the relative extension of the C(methyl)-O and C(methylene)-O bond distances in this compound. An rgC-O bond distance of 1.428(9) Aring is tentatively predicted for ethylene oxide.

Journal of Molecular Structure-Theochem
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2210-2728; 0166-1280