Solvent Effects on the Monomer/Hydrogen-Bonded Dimer Equilibrium in Carboxylic Acids: (+)-(S)-Ketopinic Acid as a Case Study

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• 作者：Dr. Pilar Gema Rodrí ; guez Ortega ; Prof. Manuel Montejo G&#225 ; mez ; Prof. Fernando M&#225 ; rquez Ló ; pez and Prof. Juan Jesú ; s Ló ; pez Gonz&#225 ; lez
• 刊名：Chemistry – An Asian Journal
• 出版年：2016
• 出版时间：June 21, 2016
• 年：2016
• 卷：11
• 期：12
• 页码：1798-1803
• 全文大小：960K
• ISSN：1861-471X

文摘

The hydrogen-bond-assisted self-association process of a chiral semirigid carboxylic acid, namely, (+)-(S)-ketopinic acid, has been studied. The multiconformational monomer/dimer equilibrium has been evaluated by means of a concentration-dependent FTIR study that enabled the experimental equilibrium constants of the dimer formation reaction (K<sub>dimsub>) to be determined in two solvents of different polarity. In CDCl<sub>3sub>, dimeric forms predominate, even in diluted solutions (<span data-equation-construct="true" class="math-equation-construct"><span data-equation-image="true" class="math-equation-image">span><span data-equation-mathml="true" class="math-equation-mathml" style="display:none">s:mml="http://www.w3.org/1998/Math/MathML">subsup xmlns:w="http://www.wiley.com/namespaces/wiley" xmlns:wiley="http://www.wiley.com/namespaces/wiley/wiley" xmlns:cr="urn://wiley-online-library/content/render" xmlns="http://www.w3.org/1998/Math/MathML">KdimCFsubsup>span>span> =5.074), whereas in CD<sub>3sub>CN the self-association process is hindered and monomers are always the main species, irrespective of solute concentration (<span data-equation-construct="true" class="math-equation-construct"><span data-equation-image="true" class="math-equation-image">span><span data-equation-mathml="true" class="math-equation-mathml" style="display:none">s:mml="http://www.w3.org/1998/Math/MathML">subsup xmlns:w="http://www.wiley.com/namespaces/wiley" xmlns:wiley="http://www.wiley.com/namespaces/wiley/wiley" xmlns:cr="urn://wiley-online-library/content/render" xmlns="http://www.w3.org/1998/Math/MathML">KdimANsubsup>span>span> =0.194). The reliability of the dimerization constants and the derived mono- and dimeric experimental fractions have been proven by means of accurate matching between the experimental vibrational circular dichroism spectra of the species and the theoretical spectra generated by considering the simultaneous weighted contributions of the concomitant monomers and dimers.