Spectroscopic studies on olefins. VII–propene and 3-methylbutene-1; proton NMR coupling constants as a function of solvent and temperature in relation to molecular geometry
✍ Scribed by Frans H. A. Rummens; Christian Simon; Claude Coupry; Nicole Lumbroso-Bader
- Publisher
- John Wiley and Sons
- Year
- 1980
- Tongue
- English
- Weight
- 702 KB
- Volume
- 13
- Category
- Article
- ISSN
- 0749-1581
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✦ Synopsis
Abstract
The proton spectra of the compounds propene (1) and 3‐methylbutene‐1 (2) have been measured in various solvents and, as neat liquids, at variable temperature. The effects of solvent and temperature on 1 are found to be small, but not negligible. The effect of temperature on the coupling constants of 2 are more pronounced, which is explained in terms of an anti‐gauche equilibrium. To obtain a consistent ΔE° value from each temperature dependent coupling constant it is necessary to correct for the non‐conformational temperature effects (obtained from 1) as well as to correct for changes in the geometry of the entire molecule, which are concurrent with a conformational transition. Such geometry changes have been calculated by a consistent force field technique, which, when coupled with INDO‐MO calculated dependencies of coupling constants on valence (and torsional) angles, provided the changes in coupling constants. The observed temperature dependence of the coupling constants of the H~2~CCH— moiety of 2 could be satisfactorily explained in this fashion. The difference in energy between the anti and gauche forms of 2 were determined as ΔE° = 127 ± 14 cal mol^−1^.