N-(4-Bromobenzoyl)-N,N′-dicyclohexylurea

In the title compound, C20H27BrN2O2, molecules are linked into one-dimensional chains through (amide)N—H⋯O=C(amide) intermolecular hydrogen bonds.


Comment
The first conscious total synthesis of a natural product was that of urea in 1828 by Wohler, which marks the beginnings of organic synthesis. Since then, many urea derivatives have been prepared and have demonstrated a wide range of uses, including fluorescence probes (Bohne et al., 2005) and anion receptors (Bondy et al., 2004).
The title compound, an N-acylurea derivative, can be conveniently prepared from dicyclohexylcarbodiimide (DCC) and p-bromobenzoic acid according to reported methods (Ślebioda, 1995). The molecular structure is shown in Fig.1. Each cyclohexyl group adopts the chair conformation, as is required for energy minimization. The two carbonyl groups are twisted substantially at the central atom, N1, with a dihedral angle of 66.43 (10)° between the O1/C7/N1 and O2/C14/N2 planes, which increases the distance between atoms O1 and N2. As a result, no intramolecular N2-H2A···O1 hydrogen bond is formed. However, molecules are linked into chains through (amide) N-H···O=C (amide) intermolecular hydrogen bonds, reinforced by C-H···O=C interactions. Surprisingly, this supramolecular arrangement is not observed in a closely related X-ray structure (Gallagher et al., 1999).
Experimental p-bromobenzoic acid (201 mg, 1 mmol) was dissolved in CHCl 3 (5 ml) and DCC (206 mg, 1 mmol) and N,N-dimethylpyridin-4-amine (122 mg, 1 mmol) were added to the solution. The resulting mixture was stirred for 1 h at 298 K. After evaporation of the solvent, a colorless solid was isolated. Single crystals suitable for X-ray structure determination were obtained by slow evaporation of a EtOAc solution over a period of several days.

Refinement
The H atom bonded to N2 was found in a difference map and refined freely to obtain an unbiased geometry for the hydrogen bonding scheme. The H atoms bonded to C were placed geometrically (C-H values were set to 1.00, 0.99 and 0.95 A° for atoms CH 2 and CH, respectively) and refined with a riding model, with U iso (H) = 1.2 times U eq (C).

Special details
Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > 2σ(F 2 ) is used only for calculating Rfactors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.