Issue 3, 1981

An electron spin resonance study of pentenynyl and pentadiynyl radicals

Abstract

Pent-2-en-4-ynyl radicals were generated from pent-1-en-4-yne and cis- and trans-1-bromopent-2-en-4-yne and observed in the trans(4) and cis(5) conformations by e.s.r. spectroscopy. The rate constant for the isomerization (5)(4) was determined by kinetic e.s.r. to be given by equation (i) and for the isomerization (4)(5) the log k1=(13.2 ± 1.3)–(47.5 ± 8.0 kJ mol–1/2.3RT) s–1(i) rate constant was found to be given by equation (ii). From the observed barriers to rotation the methane based log k–1=(13.0 ± 1.3)–(49.2 ± 8.0 kJ mol–1/2.3RT) s–1(ii) stabilization energies of (4) and (5) were estimated to be 112 and 110 kJ mol–1. E.s.r. spectra were also recorded for the 1-trimethylsiloxy-derivatives of (4) and (5), pent-2-en-4-ynyl radicals, 1-trimethylsiloxypent-2-en-4-ynyl radicals, and penta-1,4-diynyl radicals. The enthalpies of formation, structures, and stabilization energies of the hydrocarbon radicals were computed using the MINDO/3 method. The conformational interconversion of radicals (4) and (5) was also examined by MINDO/3.

Article information

Article type
Paper

J. Chem. Soc., Perkin Trans. 2, 1981, 553-560

An electron spin resonance study of pentenynyl and pentadiynyl radicals

C. Roberts and J. C. Walton, J. Chem. Soc., Perkin Trans. 2, 1981, 553 DOI: 10.1039/P29810000553

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