Solvent Effects on Conformational Change of Chemical Compounds

Solvent Effects on Conformational Change of Chemical Compounds 

Acidity of organic acids (and/or basicity of organic bases) such as carboxylic acid and amines is governed by many factors solvent, substitution, conformation and so forth. Amongst those factors the effect of conformational change is of special interest in terms of its significance 

A prototype of the abovementioned phenomena can already be seen in the simplest carboxylic acid, acetic acid (CH3CHOOH). [17] Acidity is determined by the energy or free energy difference between the dissociated and non-dissociated form, whose energetics usually depends significantly upon its conformation, e.g. the 5j/7v/antf-conformational change of carboxylate group in the compound substantially affects the acid/base equilibrium. 

The keto-enol tautomerization of acetylacetone (CH3-CO-CH2-CO-CH3), a prototype /3-diketone, has been extensively studied experimentally, and attention has been paid to its solvent effect. Although the enol form is more stable than the keto in the gas phase owing to the intramolecular hydrogen bonding, the equilibrium is known to shift toward the keto in solution as the solvent polarity increases. The tautomerization in various types of solution, which includes H2O, dimethyl sulfoxide (DMSO), and carbon tetrachloride (CCI4), was examined by means of RISM-SCF method. [18] 

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