Equilibrium studies by electron spin resonance. XII. The relationship between charge density and ion pair dissociation determined by the use of g values

Journal Article · Wed Jan 01 00:00:00 EST 1975 · J. Am. Chem. Soc.; (United States)

DOI:https://doi.org/10.1021/ja00850a013· OSTI ID:7364390

Stevenson, G R; Alegria, A E; Block, A M

The addition of salt (KI) to solutions of the free anion radical of 2,6-di-tert-butylbenzoquinone, anthraquinone, or naphthaquinone results in a decrease in the observed g value due to the formation of ion pairs. The observed g value for the anion radical in solution containing a given amount of KI has been found to be a weighted average between that for the ion pair and that for the free ion in pure hexamethylphosphoramide. The equilibrium constant for the dissociation of the ion pair to form the free anion radical has been algebraically related to the observed g value leading to the first determination of ion pair dissociation constants by the use of g values. Further, the enthalpy of ion pair dissociation has been related to the rate of change of the g value with respect to temperature (dg/dT). To use the time averaged g values the rate of ion pair dissociation and formation must be fast on the ESR time scale. This has been found for semiquinones, for which the INDO calculated electron density on the oxygen atoms available for ion pair formation is less than 6.459. When the oxygen electron density is larger than this value the free ion and ion pair are observed simultaneously. Not only are the kinetics of ion pair dissociation affected by the INDO calculated charge densities, but the K/sub eq/ decreases with increasing charge density. However,the anthrasemiquinone system yields a K/sub eq/ that is too small according to this trend. This suggests a greater polarizability of this system. (auth)

• Research Organization: Univ. of Puerto Rico, Rio Piedras
• OSTI ID: 7364390
• Journal Information: J. Am. Chem. Soc.; (United States), Vol. 97
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
ION PAIRS
DISSOCIATION
AMIDES
ELECTRON SPIN RESONANCE
IONIZATION
POLARIZABILITY
QUINONES
THERMODYNAMICS
AROMATICS
ELECTRICAL PROPERTIES
MAGNETIC RESONANCE
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
ORGANIC OXYGEN COMPOUNDS
PHYSICAL PROPERTIES
RESONANCE
400301* - Organic Chemistry- Chemical & Physicochemical Properties- (-1987)