The ~1H NMR Chemical Shift for the Hydroxy Proton of 4-(Dimethylamino)-2'-hydroxychalcone in Chloroform: A Theoretical Approach to Its Inverse Dependence on the Temperature

摘要

The inverse dependence of the chemical shift on the temperature experimentally found for the phenolic proton of 4-(dimethylamino)-2'-hydroxychalcone (DMAHC) is theoretically studied.As the temperature decreases,the solvent dielectric constant #epsilon# increases and the zwitterionic resonance form is more stabilized.Electronic calculations at the DFT level of theory were performed by immersing the solute DMAHC in chloroform cavities of different #epsilon# values.The values of the calculated chemical shifts for DMAHC as a function of #epsilon# show that the growing contribution of the zwitterionic structure justifies the experimental results.