Conformational Stability and Intramolecular Hydrogen Bonding in 1,2-Ethanediol and 1,4-Butanediol

Das, Prasanta and Das, Puspendu K and Arunan, E (2015) Conformational Stability and Intramolecular Hydrogen Bonding in 1,2-Ethanediol and 1,4-Butanediol. In: JOURNAL OF PHYSICAL CHEMISTRY A, 119 (16). pp. 3710-3720.

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Abstract

The gas-phase infrared spectra of 1,2-ED and 1,4-BD have been, recorded at three different temperatures using a multipass gas cell of 6 m optical path length. DFT calculation has also been carried out using 6-311++G** and aug-cc-pVDZ basis sets to look for the existence of intramolecular hydrogen bonding, in them from the red shift and infrared absorption intensity enhancement of the bonded O-H band compared to that of the free O-H hand. Equilibrium population analysis With 10 conformers of 1,2-ED and 1,4-BD at experimental temperatures were-carried out for the reconstruction of the Observed vibrational spectra at that temperature,using standard statistical relationships. The most abundant conformer at experimental temperatures, was identified. In 1,2-ED a red shift of 45 cm(-1) in the intramolecularly interacting O-H stretching vibrational band position and no significant intensity enhancement compared to that of-the free O-H have been observed. On the contrary, in one of the hydrogen bonded conformers of 1,4-BD, a 124 cm(-1) red shift in the O-H stretching frequency and 8.5 times-intensity enhancement for the ``bonded'' O-H compared to that of the ``free'' O-H is seen. On the basis of this comparative study, we have concluded that strong intramolecular hydrogen bonding exists in 1,4-BD. But there appears, to be weak intramolecular hydrogen bonding in 1,2-ED at temperatures of 303, 313, and 323 Km the gas phase We have found that most stable hydrogen-bonded conformers of 1,4-BD are less populated than some of the non-hydrogen-bonded conformers. Even for the 1,4-BD, the relative population of the g'GG'Gt conformer, which has a strong intramolecular,hydrogen bond, is less than what is predicted. Perhaps the intramolecular hydrogen bond plays a less Significant role in the relative stability,of the various Conformers than what has been predicted from calculations and prevails in the literature.

Item Type:	Journal Article
Publication:	JOURNAL OF PHYSICAL CHEMISTRY A
Publisher:	AMER CHEMICAL SOC
Additional Information:	Copy right for this article belongs to the AMER CHEMICAL SOC, 1155 16TH ST, NW, WASHINGTON, DC 20036 USA
Keywords:	ETHYLENE-GLYCOL; GAS-PHASE; AB-INITIO; INFRARED-SPECTROSCOPY; AQUEOUS-SOLUTION; MOLECULAR-STRUCTURE; TORSIONAL SPECTRUM; VICINAL DIOLS; DFT METHODS; SYSTEMS
Department/Centre:	Division of Chemical Sciences > Inorganic & Physical Chemistry
Date Deposited:	29 May 2015 05:53
Last Modified:	29 May 2015 05:53
URI:	http://eprints.iisc.ac.in/id/eprint/51609

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