Base strength, aromatic hydrocarbons

I 6 Aspects of Mechanisms, Processes, and Requirements for Zeolite Separation Table 6.5 Base strengths of aromatic hydrocarbons relative to HF. 

Kilpatrick, M. and Luborsky, l.E. (1953) The base strengths of aromatic hydrocarbons relative to hydrofluoric acid in anhydrous hydrofluoric acid as the solvent./. Am. Chem. Soc., 75, 577. 

Neither the relative number of benzylic hydrogens nor the base strength accounts for the slow oxidation rate of the methylnaphthalenes. Formation of radicals in the presence of aromatic hydrocarbons can lead to radical attack on the aromatic ring. Addition of phenyl or methyl radical to the ring gives a cyclohexadienyl radical that may disproportionate or dimerize, or undergo hydrogen abstraction by another radical (3, 9,13). 

Armarego109 has determined the pAa values of indolizines and aza-indolizines from their ultraviolet spectra. He found that indolizine itself has the same basic strength as a-naphthylamine (pAa 3.9) and that a methyl substituent increases the pAa by two to three units. Mason and Smith,110 studying the fluorescence spectra of various aromatic nuclei including indolizine, found no evidence to support the prediction that acid-base properties of aromatic hydrocarbons in the first electronic excited state should differ from those in the ground state. 

Colpa et al. (1963) calculated p/if(S1 )-values for a series of aromatic hydrocarbons, but could not detect fluorescence changes in the regions of acidity indicated by the Forster cycle, although fluorescence spectra attributed to proton complexes of 3,4-benzopyrene and 1,2-benzanthracene were observed in some solutions containing only the neutral molecule in the ground state. Flurry and co-workers (1963, 1966, 1967) have carried out theoretical and Forster cycle calculation on the excited state basicities of poly-methylbenzenes and Kuz min et al. (1967) have also calculated p/ (Sj)- and p/ (Tj)-values for polycyclic aromatic hydrocarbons increases in base strength of from 7 to 30 powers of ten were derived for Sj. 

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