Experimental IR, and computational ab initio and DFT B3LYP studies on spectral and structural changes, caused by the conversion of methyl cyanoacetate into carbanion

Spectral and structural changes, caused by the conversion of methyl cyanoacetate molecule into carbanion, have been studied applying a combined IRS experimental/ab initio, DFT computational approach. A good agreement has been found between experimental and scaled B3LYP/6-31++G** vibrational frequencies; the relationship between the corresponding band intensities has been only qualitative. In agreement between theory and experiment, the conversion of methyl cyanoacetate into carbanion causes strong decreases in the cyano and carbonyl stretching frequencies (with 109 and 127 cm -1 , respectively), a dramatic integrated intensity increase (51.3 fold) of the cyano stretching band and other essential IRS changes. According to both steric and electronic structure computations, the carbonyl group is conjugated with the carbanionic center more strongly than the cyano group. Except the methyl group hydrogen atoms, the whole carbanion is planar.