Dynamic proton magnetic resonance studies on complex spin systems. Non-mutual three-spin exchange in N-(trideuteriomethyl)-2-cyanoaziridine
✍ Scribed by Dieter Höfner; Ilana Tamir; Gerhard Binsch
- Publisher
- John Wiley and Sons
- Year
- 1978
- Tongue
- English
- Weight
- 686 KB
- Volume
- 11
- Category
- Article
- ISSN
- 0749-1581
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✦ Synopsis
Abstract
At room temperature and below, the proton NMR spectrum of N‐(trideuteriomethyl)‐2‐cyanoaziridine consists of two superimposed ABC patterns assignable to two N‐invertomers; a single time‐averaged ABC pattern is observed at 158.9°C. The static parameters extracted from the spectra in the temperature range from –40.3 to 23.2°C and from the high‐temperature spectrum permit the calculation of the thermodynamic quantities Δ__H__^0^ = −475±20 cal mol^−1^ (−1.987 ± 0.084 kJ mol^−1^) and Δ__S__^0^ = 0.43±0.08 cal mol^−1^ K^−1^ (1.80±0.33 J mol^−1^ K^−1^) for the cis ⇌ trans equilibrium. Bandshape analysis of the spectra broadened by non‐mutual three‐spin exchange in the temperature range from 39.4–137.8°C yields the activation parameters Δ__H__~tc~^≠^ = 17.52±0.18 kcal mol^−1^ (73.30±0.75 kJ mol^−1^), Δ__S__~tc~^≠^ = −2.08±0.50 cal mol^−1^ K^−1^ (−8.70±2.09 J mol^−1^ K^−1^) and Δ__G__~tc~^≠^ (300 K) = 18.14±0.03 kcal mol^−1^ (75.90±0.13 kJ mol^−1^) for the trans → cis isomerization. An attempt is made to rationalize the observed entropy data in terms of the principles of statistical thermodynamics.