Crystal structure of phenyl N-(3,5-dimethylphenyl)carbamate

The asymmetric unit of the title carbamate, contains two independent molecules (A and B) with similar conformations. In the crystal, they are arranged alternately, forming –A–B–A–B– chains linked by N—H⋯O(carbonyl) hydrogen bonds, which extend along the a-axis direction.


Chemical context
The The carbamate group is known in biochemistry for its role in biological processes. For example it tunes haemoglobin affinity for O 2 during physiological respiration (O'Donnell et al., 1979). Carbamates are widely employed as pharmacological and therapeutic agents (Greig et al., 2005), to inhibit different enzymes such as acetyl-and butyrylcholinesterases (Darvesh et al., 2008), cholesterol esterase (Hosie et al., 1987), elastase (Digenis et al., 1986), chymotrypsin (Lin et al., 2006) and fatty acid amide hydrolase (FAAH) (Kathuria et al., 2003). In the solid state, the carbamate group acts as both donor and acceptor in hydrogen bonding, favouring the formation of highly stable synthons. Thus, the carbamate group has been proposed as a building block for hydrogenbonded solids in crystal engineering (Ghosh et al., 2006). Most carbamate compounds of interest are phenyl derivatives, similar to the title compound whose synthesis and crystal structure are reported on herein.

Database survey
A search of the Cambridge Structural Database (Version 5.38, update February 2017;Groom et al., 2016) for the skeleton phenyl phenylcarbamate yielded 42 hits. Among these structures there are reports of two Pna2 1 polymorphs of phenyl phenylcarbamate itself, viz. YEHPOQ (Lehr et al., 2001) and YEHPOQ01 (Shahwar et al., 2009a), and those of phenyl (4methylphenyl)carbamate (YOVHOH; Bao et al., 2009) and phenyl(2-methylphenyl)carbamate (YOVLIF; Shahwar et al., 2009b). The conformations of all four reported molecules are different. For example, the aromatic rings are inclined to one another by ca 25.8 in YEHPOQ, 42.5 in YEHPOQ01, 59.0 in YOVHOH and 39.2 in YOVLIF, compared to 84.5 (1) and 85.5 (1) , respectively, in molecules A and B of the title compound.

Synthesis and crystallization
To a stirred solution of 1.0 g (5.45 mmol) of 3,5 dimethyl aniline dissolved in 100 ml of dry THF was added a calculated 5% excess of phenylchloroforamate in 50 ml of dry THF. The addition rate was such that it took 1.5 h for complete transfer. After the addition was complete, stirring was continued overnight. Excess THF was removed under vacuum at room temperature. The crude product was extracted with ethyl acetate (3 Â 100 ml), and then the organic layer was dried over anhydrous sodium sulfate. Removing the solvent under vacuum at room temperature, yielded a light-yellow product which was dried under vacuum to constant weight. Yellow  Table 1 Hydrogen-bond geometry (Å , ).

Figure 2
A view along the b axis of the crystal packing of the title compound, with the N-HÁ Á ÁO hydrogen bonds (see Table 1) shown as dashed lines. For clarity, H atoms not involved in hydrogen bonding have been omitted.

Figure 1
A view of the two independent molecules (A and B) of the title compound, with the atom labelling. Displacement ellipsoids are drawn at the 30% probability level.
block-like crystals were obtained by slow evaporation of an ethyl acetate solution at room temperature (yield 99%).

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. The N-and C-bound H atoms were positioned geometrically (N-H = 0.86 Å and C-H = 0.93-0.96 Å ) and allowed to ride on their parent atoms, with U iso (H) = 1.5U eq (C-methyl) and 1.2U eq (N,C) for the H atoms. Details of (a) the C-HÁ Á Á interactions (thin lines; see Table 1) involving adjacent aromatic rings of the title compound, and (b) the offsetinteractions [dotted lines; Cg1 and Cg3 are the centroids of rings C1-C6 and C16-C21, respectively]. For clarity, H atoms are not involved in these interactions have been omitted.

Figure 4
A view along the a axis of the crystal packing of the title compound. The hydrogen bonds are shown as dashed lines and examples of the C-HÁ Á Á interactions as black arrows (see Table 1). The rings involved ininteractions are blueÁ Á Áblue (Cg1; molecule A) and redÁ Á Áred (Cg3; molecule B). For clarity, H atoms are not involved in these interactions have been omitted.

Special details
Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All su's are estimated from the variances of the (full) variance-covariance matrix. The cell esds are taken into account in the estimation of distances, angles and torsion angles 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 > 2sigma(F 2 ) is used only for calculating R-factors(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.