Ramiah Murugan

Preparation of nitropyridines by nitration of pyridines with nitric acid

Nitration of pyridines 1a-o with nitric acid in trifluoroacetic anhydride, gave the corresponding 3-nitropyridines 6a-n in yields of 10-83%.

Prediction of gas chromatographic response factors by the PLS method

Abstract “Dietz” response factors (RF) have been measured under standard conditions for 100 substituted benzenes and pyridines. The data have been treated by the partial least squares (PLS) method, using as explanatory variables the molecular weight together with structural features such as the numbers of atoms of each element and of multiple bonds, functional groups, etc. The “Dietz” RF are explained to 84% of the variance by three PLS components. It is shown that Dietz RF can be predicted from the structural formulae for many classes of compounds with an average deviation of 0.05 within the model and 0.09 out of the model. This should be of considerable utility in the quantitative analysis of complex product mixtures by GC/MS, especially for those cases where some or all of the products are unavailable. The PREDICT.EXE program for the PC and Fortran code, PREDICT.FOR, as well as the raw data set used to derive the model are included on disk.

Acyl derivatives of cyclic secondary amines. Part 1. Dipole stabilization of anions: the cumulative effect of two stabilizing groups

Lithiation studies with diacylimidazolidines, diacylhexahydropyrimidines, and triacylhexahydro-1,3,5-triazines indicate that no substantial increase in carbanion stability occurs as a results of the introduction of the second stabilizing group. Relative energies are calculated for three conformers of lithiated diformylimidazolidine, six conformers of lithiated diformylhexahydropyrimidine, and eight conformers of lithiated triformylhexahydro-sym-triazine. For the six-membered rings, conformers with equatorial lithium are always more stable those those with axial lithium. Although equatorial syn-syn conformers (with double O–Li co-ordination) are more stable than equatorial syn-anti, the difference is significantly less than that found between the corresponding syn-anti and (least stable)anti-anti conformers.

Electrophilic substitution of heteroaromatic compounds. Part 54. Intramolecular base-catalysed hydrogen exchange at the 3-position in substituted pyridines

Various O-linked substituents at the 4-position of a pyridine ring enhance the rate of base-catalysed hydrogen exchange at the 3,5-ring positions. An intramolecular proton-abstraction mechanism is proposed.

Acyl derivatives of cyclic secondary amines. Part 2. Dynamic 1H and 13C nuclear magnetic resonance studies on bis- and tris-amides: equilibria of syn-anti interconversion

Variable-temperature 1H and 13C n.m.r. spectra are reported for 1,3-diacylimidazolidines, 1,3-diacylhexahydropyrimidines, and 1,3,5-triacylhexahydro-sym-triazines. Peaks for the individual conformers found at low temperature were assigned by using model compounds, from relative intensities, and by internal consistencies. Conformer populations are deduced and compared with those calculated assuming energy differences arise only from dipole-dipole interactions and good agreement is noted.