Vibrational spectra and conformational composition of ethylene glycol dinitrate in solid phases

Abstract

8. J. A. Barltrop and J. D. Coyle, Excited States in Organic Chemistry [Russian transla- tion], Moscow (1978), pp. 67"70. 9. I. S. Ioffe and V. F. Otten, Zh. Organ. Khim., 32, No. 4, 1196-1201 (1962). i0. I. S. Ioffe and V. F Otten, Zh. Organ. Khim., i, No. 2, 343-346 (1965). ii. Yu. Yu. Lur'e, Handbook on Analytical Chemistry [in Russian], Moscow (1979), p. 322. 12. B. Stevens, N. Conneily, and P. Suppan, Spectrochim. Acta, 2-2, No. 12, 2121-2122 (1966). 13. Sharma Ashutash and M. K. Machwe, Curr. Sci. (India), 5_~i, No. 13, 657-659 (1982). 14. M. D. Galanin, A. A. Kut'enkov, V. N. Smorchkov, et al., Opt. Spektrosk., 53, No. 4, 683-689 (1982). 15. V. Ya. Artyukhov, R. T. Kuznetsova, and R. M. Fofonova, Zh. Prikl. Spektrosk., 37, No. 4, 576-580 (1982). 16. F. V. Schaefer (ed.), Dye Lasers, Springer, New York (1977). VIBRATIONAL SPECTRA AND CONFORMATIONAL C~9OSITION OF ETHYLENE GLYCOL DINITRATE IN SOLID PHASES G. A. Beresneva, L. V. Khristenko, UDC 539.194.01 S. V. Krasnoshchekov, and Yu. A. Pentin The authors of [i] studied the vibrational spectra of ethylene glycol dinitrate (EGDN) and showed that in the liquid state this compound consists of a mixture of conformers, while in the crystalline state it exists in the form of two modifications: a metastable one (crystal II), obtained by intense supercooling the liquid, and a stable modification (crystal I) obtained by either slowly cooling the liquid, or by heating the metastable modification to a temperature of -50~ If we assume that in a restrained internal rotation around the C--C and C--O bonds, the "staggered" conformations will be stable, while the --C-~NO= groups are planar, then EGDN can exist in the form of ten different nuclear equilibrium configurations. Figure i shows these possible conformations of EGDN. The authors of [i] suggested that each of the solid modifications is formed by only one of the ten possible conformers, which were identified from the data of rotation isomerism of ethyl nitrate [2] and the results of vibrational calculation carried out in [3], using force constants obtained by the MINDO/2 method. In this present work, the IR spectra of crystals I and II were recorded on a Bruker Fourier-type spectrometer with a higher,resolution than that obtained in [i], including the region below 400 cm -I, in which the IR spectra of crystals have not yet been studied. Figure 2 shows the IR spectra of a vitreous EGDN and two of its crystalline modifications (I and II). In the spectrum of crystal II in the 100-900 cm -I region, a region of skeletal stretch- ing and deformational vibrations, which are most sensitive to rotation isomerism, the number of bands exceeds that required for one nuclear configuration at equilibrium. On crystal II § crystal I transition, the bands at 213, 390, 588, 662, 715, 862, 928, i036,'1237, 1392, 1431, 1460, and 1646 cm -i disappear. Bands at 364, 405, 581, 656, 680, 937, 1044, 1232, 1309, 1396, 1422, 1449, and 1666 cm -~, with a low intensity in the spectrum of crystal II, become markedly more intense, and the number of bands in the spectrum of crystal I in the 100-900 cm -i region corresponds to the number of bands for one Conformer. These facts indicate that crystal II is formed by at least two conformers, and crystal I by one conformer, and the conformer forming crystal I is also included in the composition of crystal II. For a more reliable identification of the conformers forming crystals I and II, we calculated the frequencies and forms of normal vibrations of all the ten possible conformers of EGDN. The calculations were carried out in an independent system of local symmetry co- ordinates, by a standard method [4]. The natural coordinates introduced, which are repre- Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 48, No. 6, pp. 946-952, June, 1988. Original article submitted April 8, 1987. 614 0021-9037/88/4806-0614512.50 9 1988 Plenum Publishing Corporation