par De Mare, George 
;Peterson, Michael R.
Référence Journal of molecular structure. Theochem, 104, 1-2, page (115-130)
Publication Publié, 1983
;Peterson, Michael R.Référence Journal of molecular structure. Theochem, 104, 1-2, page (115-130)
Publication Publié, 1983
Article révisé par les pairs
| Résumé : | The geometry of cyclopropanecarboxaldehyde has been optimized completely at each critical point in the torsional potential curve for-CHO group rotation by analytic gradient (force) methods at the STO-3G, 3-21G and 6-31G* basis set levels. In agreement with the available gas-phase electron-diffraction and microwave spectroscopy results, minima in the torsional potential energy curves are located only at the cis and trans conformations. The STO-3G basis computations place the cis 1.4 kJ mol-1 above the trans conformer and predict the barrier for the trans → cis rotation to be 13.8 kJ mol-1 at θ = 99.3° The computations with the 3-21G and 6-31G* basis sets predict (i) that the cis is more stable than the trans rotamer by 7.0 and 1.2 kJ mol-1, respectively, (ii) that the cis → trans rotational barrier is 31.7 and 24.3 kJ mol-1, respectively and (iii) that the transition state is located at θ = 101.5 and 99.9°, respectively. The geometrical parameters obtained are compared with the corresponding values for vinylcyclopropane, acetaldehyde and glyoxal. Evidence is found for important geometry changes due to the attraction between the oxygen and adjacent ring hydrogen atoms in the cis-cyclopropanecarboxaldehyde rotamer. Electric dipole moments were computed with the optimized geometries at each critical point. Those obtained with the STO-3G basis are unsatisfactory, being less than 65% of the experimental values. In contrast, the dipole moments computed with the 3-21G and 6-31G* basis sets (which are identical within 0.02 D for the same rotamer) are larger than the experimental values by less than 8%. © 1983. |
