Comparison of hydrogen bonding in 1-octanol and 2-octanol as probed by spectroscopic techniques.
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.
Palombo
Francesca
F
Dipartimento di Chimica, Università di Perugia, Via Elce di Sotto, 8, I-06100 Perugia, Italy.
Sassi
Paola
P
Paolantoni
Marco
M
Morresi
Assunta
A
Cataliotti
Rosario Sergio
RS
D020003:1-Octanol / Q000737:chemistry*; D006860:Hydrogen Bonding; D000442:Octanols / Q000737:chemistry*; D013053:Spectrophotometry; D013816:Thermodynamics
D000442:Octanols; C067943:2-octanol; D020003:1-Octanol