Crystal Packing of Long-chain Aliphatic Molecules: A Continuous Symmetry Measures Approach

Abstract

Bulk crystals of normal Alkanes n-CnH2n+2 and Langmuir monolayers of alkane derivates show similar phase diagrams, including rotator phases and the low-temperature herringbone structure. By varying the temperature, the interactions between neighboring chains will be altered due to the increase in atomic movement, thus modifying the structure in which the chains pack. In this project, a study will be carried out to be able to compare the theoretical and experimental packing modes for normal alkanes. To carry out these comparisons we made a search in a crystallographic database (Cambridge Structural Database) for the structures needed to perform a crystallographic analysis as well as some molecular mechanics calculations for ideal infinite aliphatic chains. Once the cell parameters and atomic positions have been obtained for different compounds, a geometric analysis has been made to obtain the packing modes of the alkanes and describe their changes during phase transitions