Absolute rate constants for the addition of hydroxymethyl radicals to alkenes in methanol solution

✍ Scribed by J. Q. Wu; H. Fischer

• Publisher: John Wiley and Sons
• Year: 1995
• Tongue: English
• Weight: 753 KB
• Volume: 27
• Category: Article
• ISSN: 0538-8066
• DOI: 10.1002/kin.550270207

✦ Synopsis

Absolute rate constants and their temperature dependencies were determined for the addition of hydroxymethyl radicals ( C H 2 0 H ) to 20 monoor 1,l-disubstituted alkenes (CH2 = C X Y ) in methanol by time-resolved electron spin resonance spectroscopy. With the alkene substituents the rate constants at 298 K (k298) vary from 180 M-ls-l (ethyl vinylether) to 2.1 . lo6 M-ls-' (acrolein). The frequency factors obey log A/M-ls-' = 8.1 5 0.1, whereas the activation energies (E,) range from 11.6 kJ/mol (methacrylonitrile) to 35.7 kJ/mol (ethyl vinylether). As shown by good correlations with the alkene electron affinities (EA), log k29~lM-ls-l = 5.57 + 1.53 . EA/eV (R2 = 0.820) and E, = 15.86 -7.38 . EA/eV (R2 = 0.773), hydroxymethyl is a nucleophilic radical, and its addition rates are strongly influenced by polar effects. No apparent correlation was found between E, or log k298 with the overall reaction enthalpy.