Nuclear magnetic resonance study of hindered rotations of the π-bonded ring in crystalline benzenetricarbonylchromium
- 1 January 1975
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in Journal of the Chemical Society, Faraday Transactions 2: Molecular and Chemical Physics
- Vol. 71, 207-214
- https://doi.org/10.1039/f29757100207
Abstract
N.m.r. broad line measurements on crystalline benzenetricarbonylchromium at various temperatures show two narrowings of the proton absorption line-width, centred at about –165 and –45°C. The corresponding activation energies are E1= 3.4 ± 0.4 and E2= 7.2 ± 0.6 kcal mol–1. A more reliable value for the activation energy E1, obtained by measurements of the spin-lattice relaxation time, results in E1= 4.2 ± 0.1 kcal mol–1. The low temperature narrowing is attributed to the rotation of the arene groups, in agreement with our second moment calculations of the absorption signal. Comparison of E1 with the corresponding activation energies for C6H6 and C6F6 indicates that most of the rotational hindrance is due to the packing forces. Hypotheses are advanced for the interpretation of the second line-width narrowing.Keywords
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