6-Bromo-2-methylsulfanyl-1,3-benzothiazole

The title molecule, C8H6BrNS2, is almost planar with a dihedral angle of 0.9 (1)° between the benzene and thiazole rings. The values of the geometry-based index of aromaticity (HOMA) and the nucleus-independent chemical shift (NICS) for the two cyclic fragments of the title molecule are 0.95 and −9.61, respectively, for the benzene ring, and 0.69 and −7.71, respectively, for the thiazole ring. They show that the benzene ring exhibits substantially higher cyclic π-electron delocalization than the thiazole ring. Comparison with other similar benzothiazole fragments reveals a similar trend.

The title molecule, C 8 H 6 BrNS 2 , is almost planar with a dihedral angle of 0.9 (1) between the benzene and thiazole rings. The values of the geometry-based index of aromaticity (HOMA) and the nucleus-independent chemical shift (NICS) for the two cyclic fragments of the title molecule are 0.95 and À9.61, respectively, for the benzene ring, and 0.69 and À7.71, respectively, for the thiazole ring. They show that the benzene ring exhibits substantially higher cyclic -electron delocalization than the thiazole ring. Comparison with other similar benzothiazole fragments reveals a similar trend.

Experimental
It has been shown for benzothiazoles that global aromaticity is always higher than for the single five-membered ring (Karolak-Wojciechowska et al., 2007). This is the consequence of the thiazole ring conjugation with fully aromatic benzene ring.
To estimate cyclic π-electron delocalization in our system we used geometry based Harmonic Oscillator Model of Aromaticity. HOMA can be calculated for both the whole molecule or individual moiety. For the title benzothiazole moiety HOMA equals 0.82, whereas for thiazole ring 0.69 and 0.95 for benzene ring (Table 1). The value of HOMA for benzene ring is higher than for thiazole, what is additionally corroborated by the magnetic indices of aromaticity. For thiazole ring NICS(0) = -7.71, NICS(1)zz = -15.89. For benzene ring NICS(0) = -9.61, NICS(1) zz = -25.44. For comparison we calculated HOMA indices for other 9 compounds derived from the Cambridge Structural Database (Allen, 2002) containing benzothiazole fragment. All of them showed similar trend. Selected compounds had to fulfill the following criteria: (i) R factor below 5%, (ii) only the carbon atom of the methylthio group bears a substituent and this substituent binds through the carbon atom, (iii) benzothiazole moiety is not embedded in heterocyclic ring. The values of indices are gathered in Table 1. HOMA values indicate large π-electron delocalization in benzene ring in all compounds. Thiazole ring shows lower aromaticity than the global HOMA in all cases. Noteworthy, the variation of indices for both fragments is very small, but it is fair to note that the structure modifications are not important as only the substituents joined to the carbon atom of methylthio group change. The calculations were carried out using Gaussian09 program (Frisch et al., 2009), starting from the X-ray geometry.
Effective core potential for the bromine atom at the B3LYP/LANL2DZ theoretical level was used. NICS values were computed at GIAO/B3LYP/6-311+G**; the NICS(1) points are 1 Å above ring centres, perpendicular to the averaged planes of the rings. HOMA indices were calculated using personal program by one of the authors (M. A. D.).

Refinement
H atoms were placed in calculated positions with C-H = 0.95-0.98 Å, and refined in riding mode with Uiso(H) = 1.2-1.5

Ueq(C).
Figures Fig. 1. The molecular structure of the title compound showing displacement ellipsoids at the 50% probability level.

Special details
Geometry. All e.s. 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 > σ(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.