Experimental and theoretical studies on the thermodynamics and properties of 2-substituted 6(4)-methyl-1,4(1,6)-dihydropyrimidine-5-carboxylates were undertaken by ¹H NMR measurements and DFT (density functional theory) calculations. The ratios of tautomers a/b of dihydropyrimidines (DPs) 1, 2, and 3 were determined under various conditions to reveal the effects of temperature, solvent, and concentration on the thermodynamic data. The observed results, the free energy differences (ΔG), enthalpy differences (ΔH), and entropy differences (ΔS), are discussed in terms of the molecular structures, dipole moments (DM), and the electrostatic potential maps calculated by the DFT to clarify the nature of the DPs.

通过¹ H NMR测量和DFT（密度泛函理论）计算，对2-取代的6（4）-甲基-1,4（1,6）-二氢嘧啶-5-羧酸酯的热力学和性质进行了实验和理论研究。互变异构体的比例一个/ b的二氢嘧啶（DPS）1，2，和3在各种条件下测定以显示温度，溶剂和浓度对热力学数据的影响。观测结果，自由能差（ΔG），焓差（ΔH）和熵差（ΔS）的分子结构，偶极矩（DM）和由DFT计算得出的静电势图以阐明DP的性质进行了讨论。