Chain Length Dependence of the Thermodynamic Properties ofn-Alkanes and their Monosubstituted Derivatives

Abstract

The present work presents an extensive literature survey and analysis of the heat capacity and thermodynamic properties of fusion, vaporization, and sublimation for the linear hydrocarbons and several terminally substituted homologous series. The successive introduction of methylene groups on the relative stability of the solid and liquid phases is analyzed and discussed based on the chain length dependence of the enthalpies, entropies, and Gibbs energies of phase transition. An odd–even alternation is observed in the fusion and sublimation equilibria. The improved packing patterns of even-numbered n-alkanes is reflected in higher values of melting temperatures and thermodynamic properties of phase transition. Molar heat capacities in liquid phase of n-alkanes derivatives exhibit a linear dependence with the chain length by an increment of 31 ± 2 J·K–1·mol–1 per methylene group (−CH2−). A contribution of 4.95 kJ·mol–1 per methylene group (value corrected for 298.15 K) is derived for the increment of the enthalpy of vaporization. A constant value for the specific enthalpy of vaporization is observed for long chain compounds: 360 J·g–1. As predictable, the enthalpy of vaporization is higher for groups that can form hydrogen-bonding interactions than for plain hydrocarbons. Concerning the monohalogenated alkanes, a clear increasing of enthalpy of vaporization for the larger halogen groups is observed. Moreover, the thermodynamic results indicate that along the fusion of n-alkanes and n-alkanols, there is a decrease of around 40% in the magnitude of intermolecular interactions.

The impact of phenyl–phenyl linkage on the thermodynamic, optical and morphological behavior of carbazol derivatives

“…As discussed in recent works, a liquid with a signicant level of structuration displays a low ratio of D fus H /D sub H as most of the intermolecular interactions are not disrupted even aer a melting process. 64,70 A similar effect is observed for phenylcarbazoles ( Fig. 9).…”

Volatility Study of Amino Acids by Knudsen Effusion with QCM Mass Loss Detection

“…The propagation of low E lat to the sublimation energy is somewhat reduced by a low E pt , height of which shows modest correlation with the E lat . The higher enthalpy of sublimation of L‐methionine and L‐threonine compared to the other compounds studied should be certainly associated mainly with the contribution of the functional groups, thioester (L‐methionine) and hydroxyl (L‐threonine) groups, in analogy to the observed difference between the alkanes series . However, the effect seems to be of a different origin, based on the theoretical calculations: while L‐methionine shows larger E lat , the high sublimation energy of L‐threonine is driven by its remarkably low E pt , which is induced by stabilizing the zwitterion by a hydrogen bond between the [NH 3 ] + group and the additional β ‐hydroxyl group …”

Calculation of the Isobaric Heat Capacities of the Liquid and Solid Phase of Organic Compounds at and around 298.15 K Based on Their “True” Molecular Volume

“…The majority of experimental heat-capacity data has been found in several collective papers, of which Zabransky et al collected a series of liquid homologous linear alkanes [43] and 1-alkanols [44], while Costa et al [45] complemented these series by further homologues of liquid linear 1-alkenes, 1-alkynes, 1-alkylthiols, 1-alkylamines, 1-nitro- and 1-haloalkanes. Domalski and Hearing [46] contributed heat-capacity data of liquid and solid, saturated and unsaturated, linear and cyclical hydrocarbons.…”