ISSN:
0894-3230
Keywords:
Organic Chemistry
;
Physical Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
Equilibrium acidities and estimates of homolytic bond dissociation enthalpies (BDEs) in DMSO of the O-H bondsfor α-tocopherol, 2,6-di-tert-butylphenol, six 4-substituted-2,6-di-tert-butylphenols, and ten related phenols are reported. The presence of a 2,6-di-tert-butyl group in a phenol increases its acidity and makes substituent effects on the acidity caused by a para electron-withdrawing group larger. The BDEs of the O-H bonds in 2,4,6-tri-tert-butylphenol, 4-methoxy-2,6-di-tert-butylphenol, 4-methyl-2,6-di-tert-butylphenol and α-tocopherol, estimated by combining their pKHA values with the oxidation potentials of the conjugate anions, Eox(A-), according to the equation BDE = 1·37pKHA + 23·1Eox(A-) + C have been found to agree to within 2 kcal mol-1 with literature values (1 kcal = 4·184 kJ). Introduction of 2,6-di-tert-butyl groups into phenol and six 4-substituted phenols weakens the O-H bonds by amounts ranging from 3·6 to 10·3 kcal mol-1. These effects are attributed to increases in ground-state energies which introduce strains that are relieved when homolytic cleavage of the O-H bond forms an oxygen-centered radical where the odd electron can be delocalized into the benzene ring.
Additional Material:
3 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/poc.610080803
