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Comparison of hydrogen bonding in 1-octanol and 2-octanol as probed by spectroscopic techniques.

The journal of physical chemistry. B (2006-09-08)
Francesca Palombo, Paola Sassi, Marco Paolantoni, Assunta Morresi, Rosario Sergio Cataliotti
ABSTRACT

Liquid 1-octanol and 2-octanol have been investigated by infrared (IR), Raman, and Brillouin experiments in the 10-90 degrees C temperature range. Self-association properties of the neat liquids are described in terms of a three-state model in which OH oscillators differently implicated in the formation of H-bonds are considered. The results are in quantitative agreement with recent computational studies for 1-octanol. The H-bond probability is obtained by Raman data, and a stochastic model of H-bonded chains gives a consistent picture of the self-association characteristics. Average values of hydrogen bond enthalpy and entropy are evaluated. The H-bond formation enthalpy is ca. -22 kJ/mol and is slightly dependent on the structural isomerism. The different degree of self-association for the two octanols is attributed to entropic factors. The more shielded 2-isomer forms larger fractions of smaller, less cooperative, and more ordered clusters, likely corresponding to cyclic structures. Signatures of a different cluster organization are also evidenced by comparing the H-bond energy dispersion (HBED) of OH stretching IR bands. A limiting cooperative H-bond enthalpy value of 27 kJ/mol is found. It is also proposed that the different H-bonding capabilities may modulate the extent of interaggregate hydrocarbon interactions, which is important in explaining the differences in molar volume, compressibility, and vaporization enthalpy for the two isomers.

MATERIALS
Product Number
Brand
Product Description

Sigma-Aldrich
(±)-2-Octanol, ≥96.0% (GC)
Sigma-Aldrich
(±)-2-Octanol, ReagentPlus®, ≥99.5% (GC)
Sigma-Aldrich
(S)-(+)-2-Octanol, 99%
Sigma-Aldrich
2-Octanol, ≥97%, FG
Sigma-Aldrich
2-Octanol, 97%