Methylene phenyl substituent effects

Phenyl Substituent Effects on Methylene, Nitrenium Ion, and Nitrene... 

The solvent effect on the azo-hydrazone equilibrium of 4-phenylazo-l-naphthol has been modelled using ab initio quantum-chemical calculations. The hydrazone form is more stable in water and in methylene chloride, whereas methanol and iso-octane stabilise the azo form, The calculated results were in good agreement with the experimental data in these solvents. Similar studies of l-phenylazo-2-naphthol and 2-phenylazo-l-naphthol provided confirmation. Substituent effects in the phenyl ring were rationalised in terms of the HOMO-LUMO orbital diagrams of both tautomeric forms [53]. 

Intersystem crossing rate constants of ortho- and meto-substituted singlet phenyl nitrenes are presented in Table 3. Mono- and di-ort/io-fluorine substituents have no influence on ISC rate constants. No effect with meta, metfl-difluoro substitution is observed either. Pentafluoro substitution has no efffect on kisc in pentane although a modest acceleration is observed in the more polar solvent methylene chloride. 

The methylene group linking the benzimidazole and phenyl nuclei is best left unsubstituted although the effect of substitution on activity appears to be dependent on other substituents for example, the carbamoyl (CONH2) group has little influence on the activity of the unsubstituted methylene derivative when R3 = H (see 7), but causes a fivefold reduction when R3 = OEt. 

In summary the results observed in these studies [160] of poly(Sty-co-DVB) swelling in aromatic liquids serve to show that the method of measuring a is so sensitive that it can detect an effect caused by even the smallest modification in the molecular geometry of attached substituents, and that these differences correlate qualitatively with expectation based on the known principles of physico-organic chemistry of aromatic compounds. Since the observed a is the net effect of electronic attraction and steric hindrance between the sorbed molecule and the adsorption site, i.e. the monomer unit of the polymer, it would be impossible to separate quantitatively the electronic and steric contributions of a particular substituent. The ability to make such a differentiation, however, appears to be more promising with liquids that comprise homologous series of the type Z(CH2)nH (where Z is a phenyl, chloro, bromo or iodo substituent), since the added electronic contribution to Z by each additional methylene group is well known to be extremely small when n becomes >3 [165],... 

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