Thermodynamic parameters for the reaction of 1,8-diazabicyclo [5.4.0] undec-7-ene with 4-nitrophenylnitromethane in several aprotic solvents |
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Authors: | Naja A. Ellis Colin D. Hubbard |
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Affiliation: | (1) Department of Chemistry, University of New Hampshire, 03824-3598 Durham, NH |
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Abstract: | Equilibrium constants K for reaction of the C-acid, 4-nitro/phenylnitromethane with 1,8-diazabicyclo [5.4.0] undec-7-ene have been determined in aprotic solvents over a range of temperature. Corresponding measurements have been made for the deuterated acid 4-NPNM-d2. Thermodynamic parameters K, Ho and So, for proton and for deuteron transfers are not very differet in a given solvent, but show a considerable solvent dependence. There is an increase in magnitude of K with increase in solvent dielectric constant, a finding which is consistent with formation of an ion-pair. The range of extent of exothermicity of the reaction is quite small, –40 to-65 kJ-mol–1, and the values of So (large, negative) indicate, in general, increasing solvent restriction by the product with increasing solvent polarity. A modest bathochromic solvatochromism of the product is observed as the dielectric constant increases. |
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Keywords: | C-acid-base reaction thermodynamic parameters solvent effects solvatochromism |
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