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Measuring the relative hydrogen-bonding strengths of alcohols in aprotic organic solvents.

Chemphyschem : a European journal of chemical physics and physical chemistry (2014-11-25)
Malcolm E Tessensohn, Melvyn Lee, Hajime Hirao, Richard D Webster
ABSTRACT

Voltammetric experiments with 9,10-anthraquinone and 1,4-benzoquinone performed under controlled moisture conditions indicate that the hydrogen-bond strengths of alcohols in aprotic organic solvents can be differentiated by the electrochemical parameter ΔEp (red) =|Ep (red(1)) -Ep (red(2)) |, which is the potential separation between the two one-electron reduction processes. This electrochemical parameter is inversely related to the strength of the interactions and can be used to differentiate between primary, secondary, tertiary alcohols, and even diols, as it is sensitive to both their steric and electronic properties. The results are highly reproducible across two solvents with substantially different hydrogen-bonding properties (CH3 CN and CH2 Cl2 ) and are supported by density functional theory calculations. This indicates that the numerous solvent-alcohol interactions are less significant than the quinone-alcohol hydrogen-bonding interactions. The utility of ΔEp (red) was illustrated by comparisons between 1) 3,3,3-trifluoro-n-propanol and 1,3-difluoroisopropanol and 2) ethylene glycol and 2,2,2-trifluoroethanol.

MATERIALS
Product Number
Brand
Product Description

USP
Ethylene glycol, United States Pharmacopeia (USP) Reference Standard
Sigma-Aldrich
Methanol, HPLC Plus, ≥99.9%, poly-coated bottles
Supelco
Ethylene glycol solution, NMR reference standard, 80% in DMSO-d6 (99.9 atom % D), NMR tube size 5 mm × 8 in.
Supelco
Methanol, Pharmaceutical Secondary Standard; Certified Reference Material
Sigma-Aldrich
3,3,3-trifluoro-1-propanol, AldrichCPR
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Residual Solvent - Acetonitrile, Pharmaceutical Secondary Standard; Certified Reference Material
Supelco
1-Butanol, Pharmaceutical Secondary Standard; Certified Reference Material
Sigma-Aldrich
Methanol, for residue analysis, JIS 5000
USP
1,4-Benzoquinone, United States Pharmacopeia (USP) Reference Standard
Supelco
Ethylene glycol, Pharmaceutical Secondary Standard; Certified Reference Material
Sigma-Aldrich
1-Butanol, AR, ≥99.5%
Sigma-Aldrich
Methanol, LR, ≥99%
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Methanol, anhydrous, ≥99.5%
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Methanol, AR, ≥99.5%
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Ethanol standards 10% (v/v), 10 % (v/v) in H2O, analytical standard
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Ethanol Fixative 80% v/v, suitable for fixing solution (blood films)
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1-Butanol, for molecular biology, ≥99%
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Methanol, spectrophotometric grade, ≥99%
Supelco
Melting point standard 283-286°C, analytical standard
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Methanol, suitable for HPLC
Supelco
1,4-Benzoquinone, Pharmaceutical Secondary Standard; Certified Reference Material
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2-Methyl-1-propanol, JIS special grade, ≥99.0%
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2-Butanol, SAJ first grade, ≥98.0%
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Ethylene glycol, SAJ first grade, ≥99.0%
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Ethylene glycol, JIS special grade, ≥99.5%
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1-Butanol, SAJ first grade, ≥99.0%
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Methanol, JIS special grade, ≥99.8%
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1-Butanol, JIS special grade, ≥99.0%
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Methanol, JIS 300, ≥99.8%, for residue analysis
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Methanol, SAJ first grade, ≥99.5%