Studies of NMR Chemical Shifts of Chalcone Derivatives of Five‐membered Monoheterocycles and Determination of Aromaticity Indices

A series of the chalcone derivatives of the five‐membered monoheterocyclic compounds, (E)‐1‐aryl‐3‐heteroarylpropen‐1‐ones, were prepared by aldol condensation of the corresponding aldehydes of thiophene, pyrrole, and furan with m‐ and p‐substituted acetophenones. Similar condensation of the acetyl compounds of the heterocycles with m‐ and p‐substituted benzaldehydes gave another series of the chalcone derivatives, (E)‐1‐heteroaryl‐3‐arylpropen‐1‐ones. The 13C chemical shift values (δC) of the chalcone derivatives were determined in order to find if they correlated with the Hammett σ values. A good correlation, especially for the β‐C for both series, was found for the 13C chemical shift values (δC) of the chalcone derivatives with the Hammett σ values. The chemical shift values of the β‐C of the heterocyclic compounds were plotted against those of the benzene derivatives. The resulting slopes were found to be close to the values of the aromaticity indices. Correlations of the chemical shifts of β‐Cs of 2‐4 against those of 1.