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Issue 0, 1974
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Thermodynamic effects of orientational order in chain-molecule mixtures. Part 1.—Heats of mixing of globular and normal alkanes

Abstract

Heats of mixing at 25°C have been obtained calorimetrically for alkane mixtures where component 1 is cyclohexane, 2,2-dimethylbutane or n-hexane and component 2 is a normal-Cn, n= 6,8,12 or 16, or a corresponding branched-Cn: 2,2-dimethylbutane, 2,2,4-trimethylpentane, 2,2,4,6,6-penta-methylheptane or 2,2,4,4,6,8,8-heptamethylnonane. For the three n-Cn series, the molar heats and heats per unit volume are positive and increase rapidly with n. With the branched-Cn, cyclohexane gives smaller positive heats decreasing with n, while n-hexane and 2,2-dimethylbutane show increasingly negative heats. The magnitudes and variations of the heats, and of the derived X12 parameters are inconsistent with the usual interpretation of positive ΔHM in n-alkane mixtures, i.e. an energetic weakness of methyl(end)-methylene (middle) interactions. The results are explained by energetic effects associated with a correlation of molecular orientations (CMO) in the pure components and the mixture. The CMO, studied optically by Bothorel and collaborators, is highly sensitive to molecular shape, increasing with n for pure n-Cn liquids, remaining zero for the branched-Cn, and being destroyed on mixing with spherical molecules such as cyclohexane and 2,2-dimethylbutane. Parameters (J), characterizing the CMO in the component liquids, are used to give a quantitative interpretation of the X12 and ΔHM values.

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Article type: Paper
DOI: 10.1039/F29747001465
J. Chem. Soc., Faraday Trans. 2, 1974,70, 1465-1478

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    Thermodynamic effects of orientational order in chain-molecule mixtures. Part 1.—Heats of mixing of globular and normal alkanes

    V. Te Lam, P. Picker, D. Patterson and P. Tancréde, J. Chem. Soc., Faraday Trans. 2, 1974, 70, 1465
    DOI: 10.1039/F29747001465

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