Conformational equilibria by nuclear magnetic resonance spectroscopy

✍ Scribed by Ernest L. Eliel; Michael H. Gianni

• Publisher: Elsevier Science
• Year: 1962
• Tongue: French
• Weight: 241 KB
• Volume: 3
• Category: Article
• ISSN: 0040-4039
• DOI: 10.1016/s0040-4039(00)71107-5

✦ Synopsis

RECENT publications on the conformational equilibrium constants and associated conformational free energy or enthalpy differences' of methoxyl, 2 carbethoxy13 and acetoxyl, 4. obtained by chemical methods, and of the sulfhydryl grou~,~ obtained by infrared spectroscopy, prompt us to record values of some of these and other related constants as derived by nuclear magnetic resonance spectroscopy.

The method used has been previously described.

6 It is well known that axial and equatorial protons in appropriately substituted cyclohexanes resonate at different field strength. 7 However, in as much as a monosubstituted cyclohexane, C5HloCp undergoes rapid chair inversions, the proton underlined will be seen in an average field position rather than in the position appropriate for a purely axial or purely equatorial proton.

If S is the chemical shift of the marked proton, se the corresponding shift of a purely axial proton in an equatorially substituted cyclohexane and Sa ' E.