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Issue 38, 2006
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Intra- vs. intermolecular hydrogen bonding: dimers of alpha-hydroxyesters with methanol

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Abstract

Intermolecular hydrogen bonding competes with an intramolecular hydrogen bond when methanol binds to an α-hydroxyester. Disruption of the intramolecular OH⋯O[double bond, length as m-dash]C contact in favour of a cooperative OH⋯OH⋯O[double bond, length as m-dash]C sequence is evidenced by FTIR spectroscopy for the addition of methanol to the esters methyl glycolate, methyl lactate and methyl α-hydroxyisobutyrate in seeded supersonic jet expansions. Comparison of the OH stretching modes with quantum-chemical harmonic frequency calculations and 18O labelling of methanol unambiguously prove the insertion of methanol into the intramolecular hydrogen bond. This is in marked contrast to UV/IR hole burning studies of the homologous system methyl lactate: (±)-2-naphthyl-1-ethanol, where only addition complexes were found and the intramolecular hydrogen bond was conserved. This switch in hydrogen bond pattern from aliphatic to aromatic heterodimers is thought to reflect not only a kinetic propensity but also a thermodynamic preference for addition complexes when dispersion forces become more important in aromatic systems.

Graphical abstract: Intra- vs. intermolecular hydrogen bonding: dimers of alpha-hydroxyesters with methanol

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Publication details

The article was received on 07 Jul 2006, accepted on 09 Aug 2006 and first published on 24 Aug 2006


Article type: Paper
DOI: 10.1039/B609725A
Citation: Phys. Chem. Chem. Phys., 2006,8, 4449-4460

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    Intra- vs. intermolecular hydrogen bonding: dimers of alpha-hydroxyesters with methanol

    N. Borho, M. A. Suhm, K. Le Barbu-Debus and A. Zehnacker, Phys. Chem. Chem. Phys., 2006, 8, 4449
    DOI: 10.1039/B609725A

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