• K Venkata Ramiah

      Articles written in Proceedings – Section A

    • The infra-red and Raman spectroscopic studies of amides

      P G Puranik K Venkata Ramiah

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      The infra-red spectra of primary and secondary amides have been recorded in solutions at various concentrations with particular reference to 3µ region. The apparent molecular extinction coefficients of various absorption bands in this region have been calculated at different concentrations and spectroscopic evidence is obtained for their dimeric manifestation in solutions. This method enabled the authors to assign the N–H asymmetric and symmetric stretching vibrations of the monomer and the associated molecules on a quantitative basis. The C=O stretch and the N–H in-plane deformation frequencies of monomer and associated molecules have also been assigned.

      The effect of donor solvents on the frequencies of the amino and carbonyl bands has been investigated. It is observed that C=O frequencies of these amides in donor solvents are either the same or slightly higher/than those of the same amides in solutions of chloroform, but the N–H stretching frequencies in the same donor solvents are less, the N–H deformation frequencies more, than the frequencies of the corresponding linkages in solutions of chloroform. These results are explained on the basis that the primary and the secondary amides dissociate in donor solvents and then the donor group of the solvents forms hydrogen bond with the amino group of the amide in the monomeric state. The C=O frequency of these amides in solutions of dioxane in the presence of phenol was studied and its diminution is accounted for as due to hydrogen bond formation. The Raman spectra of N-methyl formamide and dimethyl formamide and in various solvents have been recorded. Shifts observed in a number of Raman lines of these substances in mixtures are explained.

    • Spectroscopic studies of the associations of heterocyclic amines - 2-Amino-methyl pyridines and amino-quinolines

      P G Puranik K Venkata Ramiah

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      The infra-red spectra of 2-amino-methyl pyridines and amino-quinolines have been recorded in solutions at various concentrations. The N-H stretching frequencies have been assigned on the basis of the presence of intermolecular associations and primary amino group in these compounds. The bands in the region of 1600 cm.−1 have been studied in considerable detail and the N-H deformation frequencies of monomer and associated molecules have been assigned. In all the amines studied, an absorption band appears in solutions of chloroform in the region of 2950 cm.−1 which is not present in the spectra of pure amines or in solutions of carbon tetrachloride. The presence of this band has been explained as due to the associations between the free N-atom of the monomer amines and the H-atom of the chloroform.

    • Raman and infra-red spectra of amines - Toluidines andpara-amino-acetophenone

      P G Puranik K Venkata Ramiah

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      The Raman and infra-red spectra of toluidines andpara-amino-acetophenone have been recorded and the N-H stretching and bending frequencies of these amines have been assigned. The effect of solvent on the N-H stretching and deformation frequencies of the amines is investigated and their variation in solutions of pyridine is accounted for as due to the N-H ... N bonding. The empirical formula proposed by Bellamy for the N-H stretching frequencies of amines has been used for the amines under investigation. The formula is obeyed for the N-H stretching frequencies of amines and in solutions of carbon tetrachloride, chloroform or dioxane, but it breaks down for the same frequencies in pyridine. These results are explained.

    • Hydrogen bonding in amides - Electrostatic interaction and resonance

      K Venkata Ramiah P G Puranik

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      The shift in the N-H stretching frequency in the infra-red spectra of amides, due to intermolecular associations, calculated on the basis that the hydrogen bonding is essentially an electrostatic interaction and that the ionic character of the bond diminishes on hydrogen bonding. The calculated and the observed values of the frequencies agree only when the two possible resonance structures in amides are taken into consideration for calculations.

    • Hydrogen bonding in alcohols, acids and secondary amides - Electrostatic interaction and resonance

      K Venkata Ramiah P G Puranik

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      The free OH and NH stretching frequencies of methanol, ethanol, formic and acetic acids and of N-methyl acetamide are used to calculate the shift in their frequencies due to hydrogen bonding. These calculations are based on the fact that the hydrogen bonding is an electrostatic interaction and that the ionic character of the bond diminishes on hydrogen bonding. The observed and the calculated bonded stretching frequencies agree fairly in methanol and ethanol, but in formic and acetic acids and N-methyl acetamide, the agreement between the corresponding observed and calculated frequencies is obtained only when the two possible resonance structures in these molecules are taken into consideration for calculations.

    • Infrared spectroscopic studies of amides and anilides - Integrated absorption intensities and complex formation

      K Venkata Ramiah V Venkata Chalapathi

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      The integrated absorption intensities of the carbonyl band in amides and anilides and of the amide II and III bands have been measured by Ramsay’s and Wilson and Well’s methods. The intensity of the C=O band in amides is considerably greater than that in anilides and ketones, and in primary amides, it has an intermediate value between those of tertiary and secondary amides. The intensity of the amide III band in N-methyl-acetamide is considerably higher than that of the same band in the other secondary and tertiary amides. The C=O and C-N stretching frequencies, recorded in different states of aggregation in primary amides, are shown to bear a linear relation. In amides, an additional absorption band appears on the lower frequency side of the free C=O stretching absorption, in the presence of iodine. The frequency difference between these absorption bands is 25 to 45 cm.−1, indicating that the oxygen atom of the carbonyl group in amides has considerable donor strength.

    • Vibrational spectra and normal vibrations of N-methyl acetamide

      K Venkata Ramiah V Venkata Chalapathi

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      The variation in the vibrational frequencies of N-methyl acetamide in solutions compared to the frequencies of the pure amide, obtained from infra-red and Raman spectra are discussed. By splitting the molecule into two groups so that C-N is a common bond for both the groups, the normal co-ordinate treatment of N-methyl acetamide is carried out and the fundamental frequencies are calculated. On the basis of these calculations, the band at 990 cm.−1 is assigned to N-CH3 stretch. Using Gordy’s equation and the force constant for the C=O stretch, the bond order of C=O bond is calculated.

    • Proton magnetic resonance studies of the association of amino methyl pyridines

      M M Dhingra G Govil C L Khetrapal K Venkata Ramiah

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      Proton magnetic resonance studies of the solutions of (a) 2-amino, 3-methyl pyridine and (b) 2-amino, 6-methyl pyridine in carbontetrachloride show that in these molecules there is an equilibrium between monomers and hydrogen-bonded dimers. The equilibrium constants for the two cases have been obtained. Evidence has also been obtained to show that chloroform forms hydrogen bond with the ring nitrogen of these compounds. These NMR results have been compared with those obtained earlier from infra-red studies.

    • Potential constants and mean amplitudes of vibrations of N-methyl acetamide

      V Venkata Chalapathi K Venkata Ramiah

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      A normal co-ordinate treatment based on general quadratic forcefield has been applied to N-methyl acetamide molecule. In these calculations, the structure parameters of N-methyl acetamide, as given recently by Katzet al., and the Raman and infra-red data obtained by the authors are used and the potential constants have been obtained. The potential energy distribution among the various symmetry co-ordinates of each normal vibration and the mean amplitudes of vibrations have been calculated.

    • NMR studies of solvent-solute interactions of OH, SH and CH protons in dimethyl formamide and dimethyl acetamide

      C R Kanekar C L Khetrapal K Venkata Ramiah C A Indirachary

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      The H-bonding of CH3OH, C6H5SH and CHCl3 with N:N Dimethyl formamide and N:N Dimethyl acetamide has been studied using proton magnetic resonance. It has been observed that the strength of interaction is greater for dimethyl acetamide than for dimethyl formamide for the same solvent. For the same solute, however, the strength increases in the order chloroform, thiol and alcohol. The equilibrium constant for 1:1 complex of these solutes in the chloroform solvent has been estimated. In the case of benzene thiol, complex formation between the pi-electrons of the phenyl ring and the amides has been detected. It has also been observed that the exchange rate of OH proton of CH3OH in the dimethyl formamide decreases considerably.

    • Infra-red spectroscopic studies of solvent-solute interactions in parachlorophenol and thiophenol with tertiary amides

      K Venkata Ramiah C A Indira Chary P Usha Bai

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      Hydrogen bonding of O-H ... O=C and S-H ... O=C type has been studied in parachlorophenol and thiophenol with dimethyl and diphenyl amides and from the equilibrium constants, variation in the integrated absorption intensities and frequency shifts, the strength of the interaction in these complexes is discussed. In these systems diphenyl amides form weaker H-bond compared to that with the corresponding dimethyl amides. In dimethyl amides, the interaction is in the order dimethyl acetamide > dimethyl propionamide > dimethyl formamide. Similar results are obtained with diphenyl amides.

    • Vibrational spectra and normal vibrations of acetanilide and N-deuterated acetanilide

      V Venkata Chalapathi K Venkata Ramiah

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      The Raman and infra-red spectra of acetanilide and N-methylacetamide and of their N-deuterated compounds have been recorded. The vibrational frequencies of acetanilide have been assigned and the nature of the Amide I, II and III bands in acetanilide and N-methylacetamide has been investigated by the study of the changes in the frequencies of these bands in the spectra of their deuterated compounds. Acetanilide and deuterated acetanilide molecules have been subjected to normal co-ordinate treatment and the mixing up of the skeletal frequencies arising out of the in-plane vibrations has been determined. These results indicate that as in secondary amides, the amide II and amide III bands in acetanilide are due to the combined contribution ofδ (NH) andν (C-N) vibrations, but the contribution ofν (C-N) to the amide II band is less in acetanilide and deuterated acetanilide than in cases of N-methylacetamide and deuterated N-methylacetamide.

    • NMR and IR studies of the interactions of compounds containing OH group with some ethylenes

      C L Khetrapal M M Dhingra K Venkata Ramiah P Usha Bai

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      Interactions of compounds containing OH group with acrylonitrile, 2 : 3 dichloropropene, allyl cyanide and allyl halides have been studied using NMR and IR techniques. Hydrogen bonds of the type O-H ··· N have been detected. With allyl halides bonds of the type O-H ··· Cl have been detected for allyl chloride only. The value of the equilibrium constant has been calculated for O-H ··· N bonds using IR studies.

    • Normal vibrations of N, N-dimethylformamide and N, N-dimethylacetamide

      V Venkata Chalapathi K Venkata Ramiah

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      Infrared and Raman frequencies of N, N-dimethylformamide and N, N-dimethylacetamide as recorded by the authors, in the region 3100 cm.−1 to 250 cm.−1 are given. The normal co-ordinate treatment of these molecules has been carried out using general quadratic force field and the potential energy distribution of the various modes of vibrations have been calculated to study the nature of absorption frequencies arising out of the in-plane vibrations. The assignments made by the authors in the region 3100 cm.−1 to 500 cm.−1 are compared with those of Lumley Jones who assigned the frequencies on the basis of band contour studies. These calculations have enabled the authors also to assign the frequencies in the region 500 cm.−1 to 250 cm.−1 to the various bending modes of vibrations. The C-N stretching frequency in tertiary amides is considerably different from that in primary and secondary amides.

    • Raman and infrared spectra and normal vibrations of N-methylpropionamide and N-deuterated N-methyl propionamide

      P Usha Bai K Venkata Ramiah

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      Raman and infrared spectra of N-methyl-propionamide and N-deuterated N-methyl-propionamide were recorded in various states of aggregation—pure amide, in solution and vapour state—and the frequency changes of the functional groups were studied. The implane skeletal vibrations of N-methyl-propionamide and its deuterated compound were calculated treating these molecules as six-body problems. The distribution of potential energy of each normal mode among various symmetry co-ordinates was calculated and the nature of the amide I, II and III bands and the mixing up of the inplane vibrational frequencies of N-methyl-propionamide and the deuterated amide are discussed on a quantitative basis.

    • Halogen substituted amides - Part I-A CNDO calculation of N-methylcarbomyl chloride and N-chloroacetamide

      L Srinivasa Rao V Venkata Chalapathi K Venkata Ramiah

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      A CNDO calculation was carried out for N-methyl carbomyl chloride and N-chloroacetamide. The charges, bond orders, and dipolemoments of these molecules were calculated and the effect of chlorine substitution on amide group is discussed. The two highest filled M.O.s in both molecules are almost degenerate; they are a pi-orbital followed by the non-bonding oxygen lone pair orbital. In case of N-chloro acetamide the charges, bond orders and dipolemoments have been calculated for both cis and trans structures and the average dipolemoment calculated on the basis of infrared data and orbital calculation is reported.

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