Ідентифікація кластерної будови вуглеводнів за температурами плавлення

Abstract

The presence of oscillatory changes in the substance properties in homologous series of hydrocarbons, in particular for the melting point, is analyzed. A method for predicting the mass burnout rate of normal structure alcohols and alkanes on the basis of melting point values to account for oscillations is presented. It is proved that the tendency to increase melting temperatures depending on the number of carbon atoms in the molecule for selected homologous series of hydrocarbons (alkanes, alkenes, alkynes, cycloalkanes of normal structure) has a certain oscillation by the principle of "even-odd" molecules or gradation deviation from linearity. It is shown that the similarity of this dependence between homologous series arises if alkenes and alkynes are considered as shorter molecules than the corresponding alkanes, and cycloalkanes – as longer. It is accepted as a working hypothesis that this is due to the presence of the smallest structural unit of matter in the clusters form with a certain coordination number. The oscillation properties of the substance are explained by the fact that clustering can occur both at the final carbon site in the molecule and at other carbons in the chain of the molecule, and this fact depends on the "parity-oddness". Based on the known values of melting temperatures in homologous series, the possible structure of clusters is proposed. It is shown that the obtained values of equivalent lengths for these clusters correlate with the corresponding melting temperatures. This correlation is described by the third degree polynomial, which gives an approximation coefficient of 0.995 and a mean deviation of 7.1 K. An approximation formula for calculating these classes melting point of hydrocarbons based on the values of equivalent molecular weight and cluster length has been developed. This calculation is characterized by an approximation factor of 0.997 and a mean deviation of 4.2 K. Emphasis is placed on the possibility of improving the calculation convergence with the substance properties, provided that the structure of the clusters is clarified.