Intra- and intermolecular N–H•••O=C hydrogen bonds in 1-acyl urea compounds: Synthesis, X-ray structure, conformational and Hirshfeld surface analyses of 1-(2,3-dichlorophenyl)-3-pivaloylurea

Abstract

Reaction of freshly prepared pivaloyl isothiocyanate with 2,3-dichloroaniline afforded the 1-(2,3-dichlorophenyl)-3-pivaloylthiourea intermediate (2) which was efficiently converted into the title urea (3) by grinding with wet silica supported potassium permanganate under solvent-free conditions in an excellent yield and purity. The structure was confirmed by the spectroscopic, elemental analysis and single crystal X-ray diffraction data. In the most stable conformation, the two C=O groups adopt a mutually opposite orientation. Intramolecular N–H•••O=C hydrogen bond occurs between the carbonyl (C=O) and urea (–NH) groups forming a six membered pseudo-ring that stabilize the most stable form. The bonding nature of this interaction has been scrutinized by using Natural Bond Orbital (NBO) population analysis, demonstrating the occurrence of a strong hyperconjugative remote interaction between the donor lone pairs located on the carbonyl oxygen and the N–H group. To visualize the intermolecular interactions in the crystal of the title compound, a Hirshfeld surface (HS) analysis was also carried out demonstrating that hydrogen-bonding and van der Waals interactions were the dominant interactions in the crystal packing. The urea groups form centrosymmetric dimers connected by intermolecular N–H•••O=C hydrogen bonds in a R22(8) motif. The 2,3-dichloro substitution has important effects on the packing stability, mostly via H•••Cl contacts, with H•••Cl/Cl•••H contributions of 26.1% of the intermolecular interactions.