Abstract
X-ray diffraction characteristics are obtained for odd monocarboxylic acids (fatty acids) C n H2n O2 with n = 11, 13, 15, 17, 19, and 21. It is found that all original samples (reagents) of these acids are two-phase. There are found the following modifications: for the acid with n = 11 triclinic Tc (space group P-1) and monoclinic M 3 (space group P21/c); for n = 13 triclinic Tc (space group P-1) and bilayered monoclinic 2M (space group A2/a); for n = 15, 17, 19, 21 two monoclinic M 1 (space group P21/a) and M 3 (space group P21/c). It is demonstrated that the homological series and individual homologues of fatty acids manifest noticeable crystal chemical features such as morphotropism and polymorphism, respectively. Thermal phase transformations of odd fatty acids are studied using pentadecanoic acid C15H30O2 as a representative example. It is found that near the melting point (52 °C) within the temperature range of 45–50 °C the monoclinic phase M 1 of this acid undergoes a polymorphic transformation in the high-temperature bilayered monoclinic phase 2M. The data obtained are compared to those reported in the literature. An express standardless test is developed for the determination of homologues (the n value) and polymorphic modifications of monocarboxylic acids.
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Original Russian Text © 2014 Y. M. Trushkina, E. N. Kotel’nikova.
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Translated from Zhurnal Strukturnoi Khimii, Vol. 55, Supplement 1, pp. S77–S84, 2014.
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Trushkina, Y.M., Kotel’nikova, E.N. Morphotropism, polymorphism and behavior on heating of odd monocarboxylic acids C n H2n O2 in the homologous series n = 11–21. J Struct Chem 55, 1260–1267 (2014). https://doi.org/10.1134/S0022476614070099
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DOI: https://doi.org/10.1134/S0022476614070099