Odd-even effect in n-alkane systems: A molecular dynamics study

TL;DR

This study uses molecular dynamics simulations to analyze the odd-even effect in n-alkanes, revealing property alternations related to molecular shape and density variations, with anomalous behavior observed in heptane.

Contribution

It provides a comprehensive simulation analysis of the odd-even effect across multiple properties in n-alkanes, highlighting the roles of molecular shape and density.

Findings

Odd-even alternation observed in melting point, density, and dynamics.

Heptane shows anomalous behavior in most properties.

Rotational and translational dynamics exhibit odd-even behavior.

Abstract

Alternation in various properties of n-alkanes (CnH2n+2) as a function of carbon content (n) is termed odd-even effect. Here, we report a comprehensive molecular dynamics simulation study on n-alkane systems carried out with n ranging between 3 (propane) and 8 (octane), examining the odd-even effect in melting point, density, intramolecular conformational ordering, translational and rotational motion. We observe an odd-even alternation in these properties, but with heptane (n = 7) exhibiting anomalous behavior for all except conformational ordering. Our simulations also show the presence of odd-even behavior in rotational and translational dynamics, below and above the melting point, respectively. The results highlight the role of both molecular shape and the variation in density and their interplay in the origins of the odd-even effect.