1-(4-Bromo-3-chlorophenyl)-3-methoxy-3-methylurea (chlorbromuron)

In the title urea-based herbicide, C9H10BrClN2O2, there exist multiple inter- and intramolecular interactions. Most notably, the intramolecular hydrogen bond between the urea carbonyl O atom and an aromatic H atom affects the planarity and torsion angles of the molecule by restricting rotations about the Ar—secondary amine N and the secondary amine N and the carbonyl C. The two N atoms in the urea fragment are in different environments. One is planar; the other, pseudo-C 3v. It is likely that the different nitrogen-atom geometries and the restricted rotations within the molecule impact the bioactivity of chlorbromuron.

In the title urea-based herbicide, C 9 H 10 BrClN 2 O 2 , there exist multiple inter-and intramolecular interactions. Most notably, the intramolecular hydrogen bond between the urea carbonyl O atom and an aromatic H atom affects the planarity and torsion angles of the molecule by restricting rotations about the Ar-secondary amine N and the secondary amine N and the carbonyl C. The two N atoms in the urea fragment are in different environments. One is planar; the other, pseudo-C 3v . It is likely that the different nitrogen-atom geometries and the restricted rotations within the molecule impact the bioactivity of chlorbromuron.

Related literature
The structure of the title compound, chlorbromuron, was determined as part of a larger project on the crystal and molecular structures of a series of herbicides, see : Baughman & Yu (1988 and references cited therein). Chlorbromuron is a urea-based herbicide that acts to inhibit photosynthesis and the oxidation of water to oxygen during the Hill reaction, see: Metcalf (1971). Typically one or more hydrogen bonds form between the -NH-or C=O groups in the urea-based herbicides and an active site in the protein, see: Good (1961 Table 1 Selected torsion angles ( ).

Comment
The crystal structure of 3-(4-bromo-3-chlorophenyl)-1-methoxy-1-methylurea, chlorbromuron (I), was determined as part of a larger project (Baughman and Yu, 1988 and references cited therein) that has focused on the crystal and molecular structures of a series of herbicides. Chlorbromuron is a urea-based herbicide that acts to inhibit photosynthesis and the oxidation of water to oxygen during the Hill reaction (Metcalf, 1971). Typically one or more hydrogen bonds form between the -NH-or C=O groups in the urea-based herbicides and an active site in the protein (Good, 1961).
Since the O1···H2 and O2···H1 intramolecular hydrogen bonds limit rotation, the structure of (I) presented here may also be close to that in vitro and/or in vivo. The limiting of the rotational degrees of freedom about the C1-N1, N1-C7, and C7-N2 bonds may influence the bioactivity of (I). A very weak intermolecular interaction between Cl1 and H9A likely exists, but, at a distance of 3.15 Å, is a little too long to be considered a true hydrogen bond, but may have some impact on packing.

Experimental
Crystals were grown by slow evaporation of a solution in EtOH.

Refinement
Approximate positions of all H's were first obtained from a difference map, then placed into "ideal" positions. Bond lengths were constrained at 0.93 Å (AFIX 43) for aromatic C-H's, at 0.96 Å (AFIX 137) for methyl C-H's, and 0.86 Å (AFIX 43) for the N-H.
U iso (H) were fixed at 1.5U eq (parent) for OH and methyl H's, and 1.2 U eq (parent) for all other H's.
In the final stages of refinement for (I), 14 very small or negative F o 's were deemed to be in high disagreement and were eliminated from final refinement. Percent decay of the three standards was calculated as the average of their σ(I)'s. Fig. 1. The asymmetric unit of (I). Displacement ellipsoids are drawn at the 50% probability levels; H atoms are drawn as small spheres of arbitrary radius. 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 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.