A number of 5-acyl rhodanines and thiorhodanines with bulky acyl groups (pivaloyl and adamantoyl), not previously available, have been synthesized. The compounds are shown to exist at the enol form. Structures have been calculated using both the MP2 approach and the B3LYP-GD3BJ functional and the 6-311++G(d,p) basis set. Hydrogen bond energies are estimated by subtracting energies of a structure with the OH group turned 180o from that of the intramolecularly hydrogen bonded one. Properties such as OH chemical shifts, two-bond isotope effects on 13C chemical shifts, electron densities at the bond critical point from AIM analysis, as well as the hydrogen bond energies show that the sterically hindered compounds have stronger hydrogen bonds than methyl or isopropyl derivatives. The combination of oxygen and sulphur derivatives enables a detailed analysis of hydrogen bond energies.
- hydrogen bonding