Part I. The Infrared Spectra and Structure of Cyanamide. Part II. The Infrared Spectra of Formamide, N,N-Dideuteroformamide, and N-Methylformamide

Citation

Rubalcava, Hector (1956) Part I. The Infrared Spectra and Structure of Cyanamide. Part II. The Infrared Spectra of Formamide, N,N-Dideuteroformamide, and N-Methylformamide. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/EN6S-9V80. https://resolver.caltech.edu/CaltechETD:etd-06242004-155629

Abstract

NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. The prismatic spectra of crystalline cyanamide and of methylene chloride solutions of cyanamide were obtained from 2 to 15 microns, and of gaseous cyanamide from 2 to 6.5 microns. High dispersion spectra in the three micron region were obtained for all these substances. The rotational structure of the antisymmetric NH2 stretching vibration shows an intensity alternation which implies that cyanamide has a planar structure, belongs to the symmetry point group [...], and has the structural formula H2NCN. Geometrical parameters of the NH2 group were obtained using the spacing of the rotational structure of the three micron band, together with a non-critical estimate of the mean value of the two smallest rotational constants, and the mean value of the NH2 stretching frequencies. The HNH angle is approximately 126[degrees], and the NH bond distance is 1.002[Angstroms]. A vibrational assignment was made with the aid of Raman data obtained by Kahovec and Kohlrausch. A normal coordinate analysis of the vibrations primarily involving the NCN stretching and the HNH scissors deformations was made. This analysis gave values, depending parametrically on the HNH bending force constant, of the CN stretching and interaction force constants. The forms of the normal modes of the three lowest frequency [...] vibrations for a plausible set of force constants was calculated, and applied to a discussion of the intensities of the absorptions of these vibrations. The high dispersion spectra of methylene chloride solutions of cyanamide showed no absorptions attributable to hydrogen-bonded polymers of cyanamide. The spectra of HCONH2, HCOND2 and HCONHCH3 were obtained in the gas and in the liquid states. The three micron spectrum of HCONH2 gas was examined under high dispersion. These data together with the results obtained by Prof. R. M. Badger in a study of vibrating mechanical models, and by Dr. R. Newman in a study of the polarized spectrum of sodium formate have been the basis for an analysis of the vibrational spectra of the formamides. An explanation has been presented for the differences between the spectra of each substance in the gas and in the liquid states based on the effects of hydrogen bonding. The spectral data have been used to support the hypothesis that formamide is a planar molecule, and an estimate of 0.993[Angstroms] for the NH bond distance based on the value of the mean frequency of the NH2 stretching vibrations has been made. The rotational structure of the three micron high dispersion band has been analyzed, and a value for the difference of the large rotational constant and the average of the two smallest rotational constants has been found which agrees, within experimental error, with the microwave value.

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