Intramolecular and intermolecular hydrogen bond formation by some ortho-substituted phenols: Some surprising results from an experimental and theoretical investigation

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DOIResolve DOI: http://doi.org/10.1021/jp900876q
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TypeArticle
Journal titleJournal of Physical Chemistry A
ISSN1089-5639
Volume113
Issue22
Pages62756288; # of pages: 14
Subject2-nitrophenol; [carbonyl; Dinitrophenol; Frequency shift; Intermolecular hydrogen bonds; IR bands; IR spectrum; Methoxy; Methoxyphenols; O-H stretching bands; OH group; Stretching frequency; Stretching region; Substituted phenol; Theoretical investigations; Theoretical modeling; Wave numbers; Binding sites; Carbonylation; Dimethyl sulfoxide; Frequency bands; Hydrogen; Hydrogen bonds; Phenols; Hysteresis motors
AbstractThe effects produced by addition of various concentrations of the strong hydrogen bond (HB) acceptor, dimethyl sulfoxide (DMSO), on the OH fundamental stretching region of the IR spectra of several o-methoxy, o-nitro, and o-carbonyl phenols in CCI4 are reported. In most of these phenols the intramolecular HB is not broken by the DMSO. Instead, the DMSO acts as a HB acceptor to the intramolecular HB forming a bifurcated intra/intermolecular HB. For o-methoxyphenols the bifurcated HBs are observed as new IR bands at much lower wavenumbers (Δv(OH) ∼ -300 cm-1) than the band due to their intramolecular HB. The formation of bifurcated HBs and the large frequency shift of their OH bands in o-methoxyphenols are well reproduced by theoretical modeling. In contrast to the o-methoxyphenols DMSO has little effect (other than causing some broadening) on the intramolecular HB OH bands of o-nitro and o-carbonyl phenols, with the single exception of 2,4-dinitrophenol. In this case, but not for 2,4-diformylphenol, the intramolecular HB OH band decreases as the DMSO concentration increases and a new absorption grows in at lower wavenumbers, indicating that DMSO can break this intra-HB and form an inter-HB, a result well reproduced by theory. Although DMSO has little effect on the O-H stretching band of 2-nitrophenol, theory indicates extensive formation (90%) of bifurcated HBs with OH stretching bands at slightly higher wavenumbers (Δv(OH) ∼ +20 cm-1) than that for the intramolecular HB OH group and 10% of a "simple" intermolecular HB in which the intramolecular HB has been broken. Theory also indicates that, with DMSO, 2-formylphenol also forms a bifurcated HB (Δv(OH) ∼ +150 cm -1), whereas 2,4-diformylphenol forms both intermolecular HBs (Δv(OH) ∼ -130 cm-1) and bifurcated HBs (Δv(OH) ∼ +165 cm-1). The IR spectrum of 2-methoxy-methylphenol shows that although an intramolecular HB conformer is dominant there is a small percentage of a "free" OH, non-HB conformer (2.1% in CCl4, 1.5% in cyclohexane). These results are quantitatively reproduced by theory. We conclude that theory can provide important insights into the formation and structure of inter, intra, and bifurcated HBs, and into their OH stretching frequencies, that are not always revealed by IR studies alone. © 2009 American Chemical Society.
Publication date
LanguageEnglish
AffiliationNational Research Council Canada (NRC-CNRC); National Institute for Nanotechnology (NINT-INNT); NRC Steacie Institute for Molecular Sciences (SIMS-ISSM)
Peer reviewedYes
NPARC number21276626
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Record identifierf48fd35d-8837-4e0d-9b6a-eb9f1006c815
Record created2015-10-13
Record modified2016-05-09
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