The conformational preference (a value) of deuterium in monodeuteriocyclohexane from deuteron integration at low temperatures
✍ Scribed by Frank A.L Anet; Daniel J O'Leary
- Publisher
- Elsevier Science
- Year
- 1989
- Tongue
- French
- Weight
- 322 KB
- Volume
- 30
- Category
- Article
- ISSN
- 0040-4039
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✦ Synopsis
The A value of deuterium in cyclohexane-d1 is shown to be 8.3 _+ I .5 cal/mol by peak integration of the deuteron NMR spectrum at -95 "C; this is in disagreement with a previous measurement (22 f 5 cal/mol) by this method reported by Aydin and Gunther, but is close to the A value (6.3 + 1.5 cal/mol) deduced previously from data on cyclohexane-di0 isotopomers.
The equatorial-axial conformational preference of deuterium in cyclohexane-dl (I), i.e., Winstein's A value for deuterium, is difficult to measure because it is very small. In cyclohexane-dll, which should have almost the same conformational equilibrium as I, three groups have found that the deuterium, within a percent or two, exhibits no conformational preference, as shown by low-field (60 and 100 MHz) lH NMR intensities at low temperature.l+ *, 3 Aydin and Gilnther4 (AG) have reported that integration of the high-field (400 MHz IH frequency) deuteron signals in