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Title: Hydrogen bonding and vapor pressure isotope effect of deuterioisomeric methanethiols

Wilson parameters, activity coefficients, association constants, and other thermodynamic functions which are derived from isothermal vapor pressure measurements between 223 and 293 K for binary mixtures of CH/sub 3/SH, CH/sub 3/SD, CS/sub 3/SH, and CD/sub 3/SD with n-hexane show the weakness of the hydrogen and the deuterium bonds of methanethiol. As far as these functions depend on the association model used for the calculation, the relation of their values to those obtained for the corresponding amines and alcohols under the same conditions attests the weak methanethiol association. While for the more strongly associated methylamines and methanols a greater energy of the deuterium bond compared to the hydrogen bond has clearly been observed, the differences between the thermodynamic functions of the systems with the SH compounds and of those with the SD compounds are insignificant. This observation as well as the fact that the vapor pressure ratios P-(CH/sub 3/SD)/P(CH/sub 3/SH) are only slightly greater than unity, that the ratios P(CD/sub 3/SD)/P(CH/sub 3/SH) are even greater than P(CD/sub 3/SH)/P(CH/sub 3/SH), and that the changes of these ratios with temperature and dilution are small in comparison to the strong increase of the corresponding quotients of the methylamines and the methanols are the consequencemore » of the weak methanethiol association. P(CH/sub 3/SD)/P(CH/sub 3/SH), P(CD/sub 3/SH)/P(CH/sub 3/SH), and P(CD/sub 3/SD)/P(CH/sub 3/SH) are represented by equations of the type ln P/sub D/ P/sub H/ = -A/T/sup 2/ + B/T where A and B are nearly additive. The low values of A and B for CH/sub 3/SD/CH/sub 3/SH in comparison to the high values for CH/sub 3/ND/sub 2//CH/sub 3/NH/sub 2/ and CH/sub 3/OD/CH/sub 3/OH reflect the weakness of the methanethiol hydrogen bonds. The constants can be related to the thermochemical and the spectroscopic data reported in the literature.« less
Authors:
; ;
Publication Date:
OSTI Identifier:
6507710
Resource Type:
Journal Article
Resource Relation:
Journal Name: J. Phys. Chem.; (United States); Journal Volume: 85:8
Research Org:
Univ. Heidelberg, Germany
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; DEUTERIUM; ISOTOPE EFFECTS; HEXANE; THIOLS; VAPOR PRESSURE; ALKANES; HYDROCARBONS; HYDROGEN ISOTOPES; ISOTOPES; LIGHT NUCLEI; NUCLEI; ODD-ODD NUCLEI; ORGANIC COMPOUNDS; ORGANIC SULFUR COMPOUNDS; PHYSICAL PROPERTIES; STABLE ISOTOPES; THERMODYNAMIC PROPERTIES 400302* -- Organic Chemistry-- Isotope Effects-- (-1987)