• B Subrahmanyam

      Articles written in Journal of Chemical Sciences

    • Strengths of some N−H… π type of hydrogen bonds

      G V G Krishna Murty B Subrahmanyam

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      Hydrogen bond formation between N−H of acetanilide and π electrons of some arenes has been studied by infrared spectroscopy. In the mixtures of CCl4 and arenes new N−H bands appeared at lower frequencies in addition to the N−H band observed in pure CCl4. The lower frequency bands are assigned to the N−H bonded to π electrons of the arenes. Formation constants of these complexes have been determined with different arene concentrations. The frequency shifts of the N−H band and the formation constants were found to increase with increase in alkyl substitution in the benzene ring. The relative frequency shifts and logarithmic values of formation constants bear linear relationship with each other.

    • Conformations of dibenzylideneacetone: An IR spectroscopic study

      G Venkateshwarlu B Subrahmanyam

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      The conformational analysis of dibenzylideneacetone has been carried out using IR spectroscopy. Appearance of a triplet C=O band is attributed to the coexistence of three conformers viz s-cis, cis, s-cis, trans and nonplanar s-trans, trans in contrast to the earlier findings which showed the existence of only two conformers. The relative proportions of the conformers are in the order s-cis, trans> nonplanar s-trans, trans> s-cis, cis in less polar solvents and nonplanar s-trans, trans> s-cis, trans> s-cis, cis in more polar solvents.

    • Conformations ofαchloroacetanilides: An IR spectroscopic study

      G Venkateshwarlu P Padmavathi Reddy B Subrahmanyam

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      The conformational analyses of α-mono, α-di and α-trichloroacetanilides have been carried out using IR spectroscopy. α-Monochloro, dichloro and trichloroacetanilides were found to exist in only one conformation in CH2Cl2 and CHC13. The existence of all these anilides in single conformation is due to intramolecular H-bond formation between N−H and Cl.

      In CH3CN, the broadening of C–0 bands of monochloroacetanilides and their bifurcation in α-dichloroacetanilides indicated the existence of two rotamers due to the breaking of chelation by the solvent.

    • Conformations of α,β-unsaturated ketones: An IR spectroscopic study

      G Venkateshwarlu B Subrahmanyam

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      The conformational analyses of substituted methyl styryl ketones and phenyl styryl ketones have been carried out using IR spectroscopy. The split in the C=O bands of these compounds is attributed to the existence of two conformations, viz.s-cis ands-trans, in equilibrium. The methyl styryl ketones exist predominantly in thes-trans form whereas phenyl styryl ketones exist in thes-cis form. In all the ketones studied the proportion of thes-trans form increases with increase in the polarity of the solvent while that of thes-cis form decreases. This shows that thes-trans form is more polar than thes-cis. The field effects between the C=O and C=C groups are found to be electrostatic repulsions which play a dominant role in the determination of the relative stabilities of thes-cis ands-trans forms over the steric effects and the electrostatic attractions between the carbonyl oxygen and the β-carbon.

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