Proton Magnetic Resonance Study of Conformational Equilibria of the Pyridinealdehydes in Solution. Comparison with Other Methods
- 1 December 1974
- journal article
- Published by Canadian Science Publishing in Canadian Journal of Chemistry
- Vol. 52 (23) , 3986-3995
- https://doi.org/10.1139/v74-595
Abstract
A p.m.r. study of the pyridinealdehydes shows that accurate spectral analysis yields long-range spin–spin coupling constants which are a precise measure of the conformational equilibria in solution. Thus, in CS2 solution the ON-trans form of 2-pyridinealdehyde is more stable than the ON-cis form by at least 2.3 kcal/mol, while in acetone solution it is 1.6 kcal/mol more stable than the cis form. Classical solvation theory allows the conclusion that in the gas phase the trans form is more stable than the cis form by about 7 kcal/mol, in contradiction to the predictions of approximate MO theory at the INDO level. The trans form of 3-pyridinealdehyde is also more stable than the cis form in polar and in nonpolar solvents. The results are compared with those of other experiments on these equilibria.Keywords
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