Graham R. Underwood

The mechanisms of spin delocalization through sigma bonds delocalization to gamma protons [1]

A study of the mechanisms of spin delocalization to γ hydrogens was conducted by investigating the change in spin density distribution upon geometrical deformation. The mechanisms are expressed in valence bond pictures. The spin densities were calculated using the SCF-MO-INDO method for the propyl radical. An empirical expression for γ-hydrogen hfscs is proposed.

Reversibly-formed ion pairs are not involved during the solvolysis of N,O-diacetyl-N-arylhydroxylamines

Abstract Appropriate oxygen-18 labeling experiments demonstrate that N,O-diarylhydroxylamines do not undergo solvolysis via the reversible formation of ion pairs. This is in total conflict with the conclusions from previous indirect kinetic studies of these ultimate carcinogen models.

The solvolysis of N-acetoxy-acetanilides: the elucidation of two major reaction pathways for model ultimate carcinogens under neutral conditions

Abstract The solvolysis of a series of N-acetoxy acetanilides has been examined in aqueous dioxane. Product distributions and rate constants reveal that, in addition to a base catalyzed hydrolysis, there are two major pathways at neutral pH: NO bond cleavage to yield nitrenium ion intermediates, and acyl-oxygen cleavage which leads to hydroxamic acid.

On the solvolysis of N-acetoxy-N-acetylaminobiphenyl: the complete lack of nitrenium ion involvement.

Abstract The solvolysis of N-acetoxy-4-acetylaminobiphenyl in 40% buffered aqueous acetone has been studied. Two processes have been identified, both leading exclusively to the formation of hydroxamic acid. By the use of 0-18 labeling, both have been shown not to involve the intermediacy of nitrenium ions.

The solvolysis of N-acetoxy-4-acetylaminostilbene: irreversible formation of nitrenium ions

Abstract Extensive kinetic studies and product analysis, coupled with 0–18 labeling experiments have shown that the solvolysis of N-acetoxy-4-acetylaminostilbene in buffered aqueous acetone proceeds via irreversible nitrenium ion formation. The conflict between this conclusion and that of a previous study is explained

A theoretical analysis of the temperature dependence of the E.P.R. spectrum of bis(trifluoromethyl) nitroxide

Self-consistent field calculations using the INDO approximation have been performed for many trial geometries of bis(trifluoromethyl) nitroxide. It has been found that the structure of minimum energy is non-planar at the nitrogen atom with a very low barrier to inversion. It is concluded that an increased amplitude of vibration of the molecule away from planarity with increased temperature is the only appropriate way to account for the temperature dependence of the E.S.R. spectrum of the radical.

The solvolysis of N-acetoxy-2-acetylaminofluorene and N-acetoxy-4-acetylaminobiphenyl: delicate balance between nitrenium ion formation and hydrolysis

The solvolysis of N-acetoxy-2-acetylaminofluorene in aqueous acetone at neutral pH proceeds exclusively with nitrenium ion formation while under the same conditions, the 4-aminobiphenyl analogue exclusive acyl–oxygen scission.

Effect of Charge on the EPR Hyperconjugative Interaction Parameter

Extensive McLachlan MO calculations have been performed on a number of methyl‐substituted radicals and radical ions to obtain a consistent set of parameters to describe the methyl group and to examine the effect of charge density on the parameter QCCH3H which relates the methyl hfsc (hyperfine splitting constant) to the spin density. It was found that there was a strong dependence of QCCH3H on charge, but it was concluded that other factors were involved and that caution should be exercised when employing β‐hydrogen hfscs as a measure of spin density.

The solvolysis of N-acetoxy-1-N-acetylaminonaphthalene and N-acetoxy-2-N-acetylaminonaphthalene: divergent chemistry and mutagenic activity

Upon solvolysis in neutral 40% aqueous acetone, N-acetoxy-1-N- and N-acetoxy-2-N-acetylaminonaphthalene exhibit completely different modes of reaction; the former reacts with nitrenium ion formation, while the latter undergoes acyl oxygen scission.

A study of the reaction of dinitrogen tetroxide with aromatic compounds

Dinitrogen tetroxide is found to nitrate aromatic hydrocarbons cleanly and in high yield. Some of the characteristics of this reaction have been examined and from competitive rate studies, inferences are drawn as to the mechanism of the reaction.