Electron spin resonance studies of t-butyl radicals at 4 K

✍ Scribed by Atieh Abu-Raqabah; Martyn C.R. Symons

• Publisher: Elsevier Science
• Year: 1991
• Tongue: English
• Weight: 333 KB
• Volume: 183
• Category: Article
• ISSN: 0009-2614
• DOI: 10.1016/0009-2614(91)80045-y

✦ Synopsis

Exposure of dilute solutions of (CH,), "C-Cl in CDSOD to "'Co y-rays at 77 K gave ESR spectra characteristic of stationary (CH,), "C' radicals. The isotropic '"C hyperfme coupling was similar to those for radicals in fluid solution, whilst theanisotropic coupling indicated a Zp, orbital population of * 0.8. The resulting p/s ratio of z 2. I is characteristic of genuinely planar radicals. Current theory suggests that effective planarity arises because ofrapid umbrella inversion, and that at low temperatures A,,( 'Q should rapidly increase as the double minimum region is entered, and also that the three methyl groups should become locked in a conformatton that has three C-H bonds giving maximum overlap with the semi-occupied orbital on the central atom. However, on cooling to ~4 K, there was no change in the overall form of the ESR spectrum except for the appearance of extra proton hyperfine features characteristic of rapid quantum tunnelling rotations of the methyl groups. Thus, there is no evidence for the predicted increase in Ai, and locked conformation of the methyl groups. We conclude that r-butyl radicals are planar or nearly so.