• N R Rao

      Articles written in Proceedings – Section A

    • Anthraquinone and anthrone series - Part IX. Chromatographic adsorption of aminoanthraquinones on alumina

      N R Rao K H Shah K Venkataraman

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      The relation between chemical constitution and chromatographic adsorbability of a series of aminoanthraqunones and their derivatives has been investigated. Of the various types of interaction of which alumina appears to be capable in the process of adsorption, the most important is hydrogen bonding between alumina and one or more proton-donor groups in the adsorptive. When anthracene, anthraquinone and a series of aminoanthraquinones and their derivatives are chromatographed on alumina, using benzene as solvent for adsorption and development, the strength of adsorption is in the following increasing order: anthracene, anthraquinone, N-methyl-1-aminoanthraquinone, 1-benzamidoanthraquinone, 1:4-bis-methylaminoanthraquinone, 1-aminoanthraquinone, 1:5-diaminoanthraquinone and N-methyl-2-aminoanthraquinone, 1:8-diaminoanthraqunione, N-methyl-1-benzamidoanthraquinone and N-methyl-2-benzamidoanthraquinone, 2-aminoanthraquinone, 1:4-diaminoanthraquinone, 1:4:5-triaminoanthraquinone, 1:2-diaminoanthraquinone, 1:4:5:8-tetraminoanthraquinone, 2:6-diaminoanthraquinone. The relative adsorption affinities are explained in terms of chelation between NH2 and CO groups, resonance interaction between NH2 and CO groups, the ability of amide groups to form hydrogen bonds, and the electron-repulsive effect of methyl groups.

    • The effect of substitution on the light absorption of naphthalene

      M R Padhye N R Rao K Venkataraman

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      A qualitative method for assigning the longest wavelength band in the absorption spectra ofα- andβ-monosubstituted naphthalene derivative to polarizations in definite directions has been devised. The longest wavelength band in the absorption spectra ofα-substituted derivatives is shown to be due to polarization along the short axis of the molecule; in the spectra of theβ-substituted derivatives the longest wavelength band is due to polarization along the long axis of the molecule. The absorption spectra of four isomeric hydroxynaphthoic acids have been determined, using dioxane as solvent. The deeper colour of 2:3-hydroxynaphthoic acid in comparison with the isomeric acids is explained as due toβ:β-disubstitution in the naphthalene nucleus. The absorption spectra of 2-methoxy-1-naphthoic acid, 2-methoxy-3-naphthoic acid and 2-methoxy-6-naphthoic acid are discussed.

    • Anthraquinone and anthrone series - Part XI. Steric hindrance in dibenzanthronyls and dibenzanthrones

      M R Padhye N R Rao K Venkataraman

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      The absorption spectra of dibenzanthrone, 16: 17-dihydroxydibenzanthrone, 16: 17-and 3: 12-dimethoxydibenzanthrone have been determined ino-chlorophenol. The bathochromic shift of the dibenzanthrone spectrum on substitution of two methoxyl groups in the 16: 17-positions of dibenzanthrone is ascribed to the over-riding tendency of the dibenzanthrone ring system to remain planar and hence force the methoxyl groups also to be coplanar with the ring system.

      The absorption spectra of 3:3′- and 4:4′-dibenzanthronyls have been reported and discussed.

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