A Study of the Liquid and Solvent Properties of Optically Active and Racemic -Methylbenzylamine

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• 作者：Andrew T. Fischer ; Richard M. Pagni ; Robert N. Compton
• 刊名：Journal of Physical Chemistry B
• 出版年：2007
• 出版时间：July 19, 2007
• 年：2007
• 卷：111
• 期：28
• 页码：8187 - 8196
• 全文大小：456K
• 年卷期：v.111,no.28(July 19, 2007)
• ISSN：1520-5207

文摘

Speed-of-sound measurements are reported for RS (racemic) and S liquid mages/gifchars/alpha.gif" BORDER=0>-methylbenzylamine (MBA) obtainedusing a modified design of previously published experimental geometry. After correcting for density changes,the resulting isentropic compressibility of the S liquid is found to be 2% larger than that of the RS racemicmixture. These data, along with proton NMR chemical shifts and published partial molar volumes, suggestthat the structures of the racemic and optically active liquids are subtly different. The magnitude of thecompressibilities and other data such as viscosity and the Kamlet-Taft parameters are consistent with themolecules in the liquids interacting via extensive hydrogen bonding. Cyclohexane, toluene, nitrobenzene,dimethyl sulfoxide, and methanol are completely miscible in MBA, as predicted from their correspondingHildebrand solubility parameters. Proton NMR, optical rotation, and IR studies were carried out on solutionsof the five solutes in MBA as a function of mole fraction. The asymmetric NH stretch of MBA was particularlyinformative in this regard. Solvation models were developed for the five solutes. The NH stretch frequencyin cyclohexane changed only slightly up to a mole fraction of 0.7 in the hydrocarbon at which point the NHstretch greatly increased by about 200 cm^-1 at a mole fraction of 1. The hydrogen-bonding network does notdissipate until there is at least 70 mol % cyclohexane in the MBA. Gaussian calcuations were also carried outto complement the ir studies.