THERMODYNAMIC PARAMETERS FOR THE REACTION OF 1,8-DIAZABICYCLO [5.4.0] UNDEC-7-ENE WITH 4-NITROPHENYLNITROMETHANE IN SEVERAL APROTIC-SOLVENTS

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, DELTAH-degrees and DELTAS-degrees, for proton and for deuteron transfers are not very different 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 DELTAS-degrees (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.