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Ab initio study on the internal rotation of five π‐conjugated hydrocarbons at MP2 level
Author(s) -
Gong Xuedong,
Xiao Heming
Publication year - 1998
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/(sici)1097-461x(1998)69:5<659::aid-qua4>3.0.co;2-u
Subject(s) - conformational isomerism , chemistry , saddle point , ab initio , isoprene , internal rotation , crystallography , computational chemistry , gaussian orbital , conjugated system , molecule , geometry , copolymer , polymer , organic chemistry , mechanical engineering , mathematics , engineering
The potential‐energy curves of internal rotation were calculated for 1,3‐butadiene at the MP2/6‐311G** level, for isoprene and 1,3‐pentadiene at the MP2/6‐311G* level, and for 2,3‐dimethyl‐1,3‐butadiene and styrene at the MP2/6‐31G* level. The geometries of the energy minima (stable conformers) and maxima (transition states) on the curves are completely optimized. For butadiene and its methyl derivatives, two stable rotamers, s ‐ trans and gauche conformers, are obtained. s ‐ trans forms have the lowest energies and gauche conformers twisted by 39.9°–48.3° around the central bond of the butadiene skeleton are, on average, 9.8 kJ/mol above the trans forms. s ‐ cis forms are rotational transition states. The computed gauche – cis barriers range from 4.30 to 11.70 kJ/mol. The regular effects of methyl substitutions at the end and central carbons are found. For styrene, the planar form is calculated to be a saddle point which is only about 1 kJ/mol higher in total energy than a twisted minimum, in which the torsional angle between the phenyl and vinyl planes is 27.4°. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 69: 659–667, 1998