Several compounds of 3-aminoquinazolin-4-(3H)-one derivative was prepared under microwave irradiation, without the requirement for chromatography and used to prepare a number of 3-monoacylaminoquinazolinones (MAQs) by reaction with acid chlorides. The barriers to rotation around the N-N bond in these MAQs have been studied as a function of temperatures using proton NMR spectra. The changes, which were found to occur in the spectra at high temperatures, are discussed in terms of hindered rotation about the N-N bond. The free energies of activation for the rate determining stereochemical process were calculated to be as high as (∼16-18 Kcal/mol) is sufficient for it to constitute a chiral axis on the NMR timescale though not on the real timescale in solution. The conformational behavior and structural stability of the optimized geometry of the MAQs rotamers were also investigated by utilizing of semiempirical, ab-initio calculations with 6-31G* basis set and Density Functional Theory (DFT) at the B3LYP with the 6-31G* basis sets. The calculated parameters are in good agreement with the corresponding experimental values...