Premium
The effect of electronegative atoms on the structures of hydrocarbons. ab initio calculations on molecules containing fluorine or (carbonyl) oxygen
Author(s) -
Allinger Norman L.,
Schäfer Lothar,
Siam K.,
Klimkowski V. J.,
Van Alsenoy C.
Publication year - 1985
Publication title -
journal of computational chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.907
H-Index - 188
eISSN - 1096-987X
pISSN - 0192-8651
DOI - 10.1002/jcc.540060502
Subject(s) - chemistry , bond length , ab initio , molecule , molecular geometry , computational chemistry , fluorine , dihedral angle , ab initio quantum chemistry methods , propionaldehyde , crystallography , single bond , hydrogen bond , alkyl , organic chemistry , aldehyde , catalysis
A series of ab initio calculations have been carried out, using the 4‐21G basis set. Ethane and propane were first studied to obtain reference points. The effect of adding an electronegative atom (fluorine, or carbonyl oxygen) onto the framework was then studied as a function of the torsional angle about the single bond. Some pronounced trends in structural changes were observed, and these can in part be correlated with hyperconjugative effects. For example, fluoroethane has bond lengths which are shorter than those in ethane itself, by 0.024 Åin the CC bond, and 0.003 Åin the α CH bonds. These changes are essentially torsionally independent. On the other hand, in propionaldehyde, the CC bond length of the methyl group and the CH bond lengths of the hydrogens attached to the alpha carbon vary as a function of the torsion angle. If the methyl CC bond in the carbonyl plane is taken as a reference, the bond stretches .016 Åwhen the torsion angle is increased to 90°, an α CH bond similarly stretches up to .007 Å. Many of these geometric changes are large, well beyond the experimental errors in modern measurements.