Comparison of Hydrogen Bonding in 1-Octanol and 2-Octanol as Probed by Spectroscopic Techniques

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.

Communication: Linking the dielectric Debye process in mono-alcohols to density fluctuations

“…Imaginary part (GPa) the bulk modulus (and the shear modulus) of 2E1H is quite modest, roughly 1 GPa at the lowest temperatures. This relaxation strength is similar to what has been found for the shear modulus of other mono-alcohols, for instance n-propanol [53], 1-octanol and 2-octanol [54], and also what is typically found for the bulk and shear modulus of non-associated, molecular liquids [50,51]. In glycerol [55] and propylene glycol [51,56] the relaxation strength is a factor of four higher.…”

Insights on the origin of the Debye process in monoalcohols from dielectric spectroscopy under extreme pressure conditions

“…It is well accepted in literature that the hydrogen bonds between hydroxyl groups in monoalcohols give rise to various molecular arrangements, with a consequent heterogeneous distribution of hydrocarbons and hydroxyl groups. [49][50][51] As pointed out by Dannhauser, 51 ring clusters would have a dipole moment nearly equal to zero, which in terms of the classical theory of Kirkwood and Fröhlich 24 results in a correlation factor g Ͻ 1. For the case of methanol and ethanol, H-bonded chains are believed to be the dominant structure, although investigations using various techniques ͓X-ray diffraction, NMR, IR/Raman, molecular dynamic ͑MD͒ simulations͔ have failed to yield any consensus on the exact structure, with some results suggesting alternative structures such as micelles or winding chainlike architectures.…”

Size distribution of associated clusters in liquid alcohols: Interpretation of simulation results in the frame of SAFT approach

“…Infrared spectroscopy thus represents the most popular experimental methods to study the microscopic structure of the hydrogen bonded systems. [2][3][4][5][6][7][8] The neutron-or x-ray diffraction techniques [9][10][11][12][13] and the dielectric relaxation 14,15 can provide further information about the structure and dynamics of the hydrogen bonded systems. Indirect information about the hydrogen bonding can be deduced also from macroscopic properties (e.g., from the viscosity measurements or PvT behaviour and phase equilibrium data).…”