Conformational preferences of sterically congested 2-imidazolidinone using X-ray analysis and computational studies. Part 1: Trans-1-acetyl-4,5-di-tert-butyl-2-imidazolidinone

The X-ray crystal structure of trans-1-acetyl-4,5-di-tert-butyl-2-imidazolidinone 2 [C13H24N2O2: MF = 240.34, monoclinic, P21/c (#14), a = 12.313(4) Å, b = 15.090(2) Å, c = 16.246(2) Å, β = 98.33(1)°, V = 2986.8(9) Å3, Z = 8, Dcalc = 1.069 g/cm3, μ(Cu-Kα) = 5.74 cm−1, F000 = 1056.00, T = 25.0 °C, R = 0.040] was determined, and confirmed the occurrence of two molecules of the s-transoid 2a and 2b which are connected together by two hydrogen bonds. The crystal cohesion is ensured by a network of intermolecular hydrogen bonding. The conformational analysis of the s-transoid 2a and 2b was performed by molecular mechanic, and showed the occurrence of one minimum for each molecule. Moreover RM1 semi-empirical and DFT/B3LYP calculations were applied to investigate the conformational preferences of the trans-1-acetyl-4,5-di-tert-butyl-2-imidazolidinone 2 and to correlate between calculated conformations and the structure in solid state. It has been found that the lowest energetic conformer computed gives the greatest correspondence with experimental solid state data.