Graeme Butt

The nature of substituent electronic effects; the existence of the π-inductive effect

Measurements of 13C n.m.r. shifts and of u.v and i.r. intensities for ω-substituted alkylbenzenes show the presence of a π-inductive effect. Various possible mechanisms contributing to such effects are analysed and the discussion is extended to related benzyl systems.

Acidities of 3- and 4-substituted pyridinium ions

Abstract The previously observed apparent discrepancy between proton transfer energies for 3- and 4-substituted pyridines as calculated at the STO-3G level and corresponding experimental values for a particular class of substituent has been further investigated by calculations at the 3–21G level. The experimental energies can be well reproduced by calculations at either the STO-3G or 3–21G bases over a wide range of substituents, but the minimal basis gives better absolute agreement overall. Some systematic deviations are noted.

Chemical shifts and charge densities in substituted nitrosobenzenes

Abstract The previous observed anomalous 13 C-NMR chemical shifts of a series of para -substituted nitrosobenzenes have been investigated using Molecular Orbital calculations with the semi-empirical CNDO/2 method and at the STO-3G basis level. The calculations show atomic electron populations at C-4, the position of attachment of the nitroso group, analogous to those found for the corresponding position in monosubstituted benzenes. Thus, groups such as CN and NO 2 lead to a decrease in the π-electron population at this position. It thus seems that the observed unexpected upfield shifts found at C-4 for these substituents is not a function of unusual electron distribution in nitrosobenzenes. The possibility of differing conformations in the nitrosobenzene group has also been found unlikely.

Infrared intensities as a quantitative measure of intramolecular interactions. Part XXVII. Substituents with donor–acceptor character: the NSO group

It is shown that the NSO group has little resonance interaction with a benzene ring in the ground state but that it is capable of resonance donation or acceptance in the presence of a second substituent, depending on the electron demand. This variable interaction is compared with that of related groups.

Stability of substituted pyrylium salts and the corresponding 2-H- and 4-H-pyrans

Abstract The stabilities of a series of 4-substituted pyrylium salts have been compared with those of the correspondingly substituted benzenes using the ab initio STO-3G basis set. It is shown that marked field and resonance effects operate in the pyrylium salts covering a range of more than 50 kcal mol −1 compared to the benzenes. The corresponding 4- H - and 2- H -pyrans that would be produced by hydride ion attack have also been studied, the 2- H -pyrans usually being the more stable. Similar substituent effects occur in these equilibria. The relative stability of the parent 2- H - and 4- H - pyrans is discussed, the 4- H -pyran being the preferred structure at the STO-3G, 3-21G and 6- 31G ∗ bases.

Novel products from attempted michael addition to 1-methyl-1,2,5,6-tetrahydropyridine-4-carbonitrile

Abstract The reaction of some phenols with the title compound, in the presence of sodium, gives 2-(2-hydroxyaryl_piperidine derivatives. Geometrical isomers have been separated, which differ in having an equatorial (A) or axial (B) cyano group on the piperidine chair (the methyl and aryl groups are equatorial in both forms). The x-ray crystallographic structures of an example of each of A and B are reported and the proton NMR spectra are assigned.

Infrared intensities as a measure of intramolecular interactions. Part XXXVI. Field-induced resonance effects

The variation of the νCC intensity for a series of disubstituted cyclohexenes indicates that the resonance interaction of a substituent with the unsaturated system can be altered by a second remote substituent. This effect is ascribed to the operation of a field-induced resonace effect.

Carbon-13 substituent chemical shifts of 4-substituted bicyclo[2.2.2]oct-1-yl cyanides

Abstract The carbon-13 substituent chemical shifts of 4-substituted bicyclo[2.2.2]oct-1-yl cyanides are a linear function of the substituent inductive parameters.