| DOI | Resolve DOI: https://doi.org/10.1039/P29860001337 |
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| Author | Search for: Ingold, K. U.1; Search for: Walton, J.C. |
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| Affiliation | - National Research Council of Canada
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| Format | Text, Article |
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| Abstract | For cyclohexylmethyl and 4-alkylcyclohexylmethyl radicals the conformer in which the CH2* group adopts the axial position and that in which the CH2* group adopts the equatorial position can both be observed by e.s.r. spectroscopy. At 140 K the axial conformers have a(H β) ca. 42-43 G; the equatorial conformers have a(H β) ca. 30-31 G. For cis-4-methylcyclohexylmethyl radicals the ratio of the concentrations of the two conformers was studied as a function of temperature and shown to depend on the rate of radical ring inversion vs. the radical lifetime; the rate constant for ring inversion was obtained. As a check on the e.s.r. results the conformational equilibrium of cis-4- methylcyclohexylmethyl bromide was studied by 1H n.m.r. spectroscopy, which gave -ΔG300°(CH2Br) = 1.91 kcal mol -1. The relative conformer concentrations were also measured as a function of temperature for cyclohexylmethyl radicals and the conformational free energy difference of the CH2* group (-ΔG 300°) was found to be 0.71 kcal mol-1. The preponderance of the conformer of the cis-4-methylcyclohexylmethyl radical with the CH3 group axial at T < ca. 175 K was attributed to the fact that the axial non-rotating CH3 group can adopt a staggered, minimum-energy conformation, whereas the axial non-rotating CH 2* group cannot because of its planarity. The barriers to rotation about the Cα-Cβ bonds in the axial radicals were found to be ca. 1.0 kcal mol-1 greater than those of the equatorial radicals; this is responsible for the greater a(H β) values of the axial radicals. The axial and equatorial conformers of cyclohexylmethyl radicals were investigated by semi-empirical SCF MO methods. |
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| Publication date | 1986 |
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| In | |
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| Language | English |
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| Peer reviewed | Yes |
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| NPARC number | 21276633 |
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| Export citation | Export as RIS |
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| Report a correction | Report a correction (opens in a new tab) |
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| Record identifier | 624e0a14-c13c-4505-b90e-a77992fb0c74 |
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| Record created | 2015-10-13 |
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| Record modified | 2020-03-17 |
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