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Intermolecular chiral assemblies in R (−) and S (+) 2‐butanol detected by microcalorimetry measurements
Author(s) -
Cogan Uri,
Shpigelman Avi,
Portnaya Irina,
Rutenberg Abraham,
Scolnik Yosef,
Shinitzky Meir
Publication year - 2012
Publication title -
chirality
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.43
H-Index - 77
eISSN - 1520-636X
pISSN - 0899-0042
DOI - 10.1002/chir.22033
Subject(s) - chemistry , isobutanol , isothermal microcalorimetry , butanol , enantiomer , racemic mixture , intermolecular force , chirality (physics) , 2 butanol , supramolecular chemistry , isothermal titration calorimetry , dilution , solvent , organic chemistry , crystallography , molecule , enthalpy , alcohol , thermodynamics , ethanol , physics , chiral symmetry breaking , quantum mechanics , nambu–jona lasinio model , quark
Supramolecular chiral assemblies of R (−) and S (+) 2‐butanol, in their neat form or when dissolved in their nonchiral isomer isobutanol, were evaluated by isothermal titration calorimetry (ITC) ensuing mixing. Dilution of 0.5 M solution of R (−) 2‐butanol in isobutanol into the latter liberated heat of several calories per mole, which was approximately double than that obtained in parallel dilutions of S (+) 2‐butanol in isobutanol. The ITC dilution profiles indicated an estimate of about 100 isobutanol solvent molecules surrounding each of the 2‐butanol enantiomers, presumably arranged in chiral configurations, with different adopted order between the isomers. Mixings of neat R and S 2‐butanol were followed by endothermic ITC profiles, indicating that, in racemic 2‐butanol, both the supramolecular order and the intermolecular binding energies are lower than in each of the neat chiral isomers. The diversion from symmetrical ITC patterns in these mixings indicated again a subtle difference in molecular organization between the neat enantiomers. It should be noted that the presence of impurities, α‐pinene and teterhydrofuran, at a level totaling 0.5%, did not influence the ITC heat flow profiles. The findings of this study demonstrate for the first time that chiral solutes in organic solvents are expected to acquire asymmetric solvent envelopes that may be different between the enantiomers, thus broadening this phenomenon beyond the previously demonstrated cases in aqueous solutions. Chirality 24:500–505, 2012 . © 2012 Wiley Periodicals, Inc.