Conformational stability of various 5-substituted orotic acid derivatives was studied by applying linear free energy relationships (LFER) to the 13 C NMR chemical shifts. The correlation analysis for the substituent-induced chemical shifts (SCS) with inductive (r I ), and various resonance (r R ) parameters were carried out through Single Substituent Parameter (SSP) and Dual Substituent Parameter (DSP) methods, and multiple regression analysis. Good Hammett correlations for all carbons were

more »

... ined, while electrophilic substituent constants better fitted for C2 carbon with electron-donor substituents. Conformational analysis of various derivatives using RB3LYP/6-311 ++G (3df,3dp) DFT method, together with 13 C NMR data suggests that most of the substituted orotic acid derivatives exist in planar conformation, except nitro and alkyl substituted derivatives. Internal rotation of carboxylic group showed significant impact on the extent of conjugative interaction making syn conformation more stable in all the derivatives studied. Further, of all 5-substituted orotic acid derivatives, diketo form proved to be the most stable form compared to zwitterionic and enol tautomeric forms. Optimized geometries and transmission effects of particular