Additivity of vaporization properties in pheromone-like homologous series

Abstract

A simple method of estimating vaporization properties of normal alkyl and (Z)- and (E)-alkenyl homologous series of pheromone-like acetates, alcohols and aldehydes with 10 to 18 carbon atoms in the chain is described. The properties hold for the (subcooled) liquid state and include vapour pressure (p_sat) and heat of vaporization (Δ_vapH) at 25 °C. An empirical QSPR model for ln p_sat and Δ_vapH is developed in terms of three easy-to-calculate structural descriptors related to the number of carbon atoms in the chain (n), the functional group characteristics (I) and the double bond position (Δ). The model, covering the property ranges of 2 × 10^–4–2 × 10¹ Pa and 60–120 kJ mol^–1, explains over 99.8% of the variance in the experimental data sets containing 295 compounds, with standard errors in ln p_sat and Δ_vapH of about 0.085 ln unit and 0.62 kJ mol^–1, respectively. It is recommended as a useful tool in designing pheromones and in fate-modelling applications in the absence of experimental data.