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

Michał A Dobrowolski; Marta Struga; Daniel Szulczyk

doi:10.1107/S160053681105015X

. 2011 Nov 25;67(Pt 12):o3446–o3447. doi: 10.1107/S160053681105015X

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

Michał A Dobrowolski ^a,^*, Marta Struga ^b, Daniel Szulczyk ^b

PMCID: PMC3239078 PMID: 22199926

Abstract

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.

Related literature

For a description of the Cambridge Structural Database, see: Allen (2002 ▶). For related structures, see: Chen et al. (2003 ▶, 2010 ▶); Li et al. (2009 ▶); Liu et al. (2003 ▶); Loghmani-Khouzani et al. (2009 ▶); Matthews et al. (1996 ▶); Saravanan et al. (2007 ▶); Zhao et al. (2009 ▶); Zou et al. (2003 ▶). For the aromaticity of benzothiazoles, see: Karolak-Wojciechowska et al. (2007 ▶). For the Gaussian program, see: Frisch et al. (2009 ▶). For the HOMA index, see: Kruszewski & Krygowski (1972 ▶); Krygowski & Cyrański (2001 ▶) and for the NICS index, see: Schleyer et al. (1996 ▶).

Experimental

Crystal data

C₈H₆BrNS₂
M _r = 260.18
Monoclinic,
a = 9.7843 (4) Å
b = 3.9514 (2) Å
c = 11.6076 (5) Å
β = 96.353 (4)°
V = 446.01 (3) Å³
Z = 2
Mo Kα radiation
μ = 5.01 mm⁻¹
T = 100 K
0.4 × 0.15 × 0.1 mm

Data collection

Oxford Diffraction Xcalibur S diffractometer
Absorption correction: multi-scan (CrysAlis RED; Oxford Diffraction, 2009 ▶) T _min = 0.422, T _max = 0.606
3437 measured reflections
1227 independent reflections
1125 reflections with I > 2σ(I)
R _int = 0.024

Refinement

R[F ² > 2σ(F ²)] = 0.017
wR(F ²) = 0.033
S = 0.99
1227 reflections
110 parameters
1 restraint
H-atom parameters constrained
Δρ_max = 0.36 e Å⁻³
Δρ_min = −0.22 e Å⁻³
Absolute structure: Flack (1983 ▶), 315 Friedel pairs
Flack parameter: 0.005 (9)

Data collection: CrysAlis CCD (Oxford Diffraction, 2009 ▶); cell refinement: CrysAlis RED (Oxford Diffraction, 2009 ▶); data reduction: CrysAlis RED; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: Mercury (Macrae et al., 2006 ▶); software used to prepare material for publication: publCIF (Westrip, 2010 ▶).

Supplementary Material

Crystal structure: contains datablock(s) I, global. DOI: 10.1107/S160053681105015X/gk2424sup1.cif

e-67-o3446-sup1.cif^{(16.3KB, cif)}

Structure factors: contains datablock(s) I. DOI: 10.1107/S160053681105015X/gk2424Isup2.hkl

e-67-o3446-Isup2.hkl^{(60.6KB, hkl)}

Supplementary material file. DOI: 10.1107/S160053681105015X/gk2424Isup3.cml

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Table 1. HOMA indices for compounds containing benzothiazole moieties.

BT = benzothiazole; MePyr = methylpyridine.

refcode	R =	HOMA (total)	HOMA (thiazole)	HOMA (benzene)
This work	H	0.82	0.69	0.95
DIDBAU^a	-C(Ph)=N—NH—C(O)—NH2	0.85	0.73	0.99
HUFSIL^b	-CH2—O—CH2—CH2—S—BT	0.83	0.69	0.98
HUYYIJ^c	-CH2—CH2—CH2—S—BT	0.84	0.70	0.98
MACMOT^d	-CH2—S—BT	0.85	0.72	0.97
	-CH2—S—BT	0.85	0.71	0.98
MACMOT01^e	-CH2—S—BT	0.85	0.70	0.98
	-CH2—S—BT	0.85	0.71	0.97
MOKJIG^f	-C(O)—C(COOCH3)=N—O—CH3	0.83	0.70	0.96
PUFGED^g	-C(O)—Ph	0.84	0.70	0.96
QOTQAS^h	-C(O)—NH-2-MePyr	0.85	0.71	0.98
ZUQQEHⁱ	-CH2—O—CH2—CH2—O– CH2—CH2—S—BT	0.83	0.67	0.98
Mean		0.84	0.70	0.97
E.s.d.		0.01	0.01	0.01

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Notes: (a) Saravanan et al. (2007 ▶); (b) Chen et al. (2010 ▶); (c) Chen et al. (2003 ▶); (d) Liu et al. (2003 ▶); (e) Zou et al. (2003 ▶); (f) Li et al. (2009 ▶); (g) Loghmani-Khouzani et al. (2009 ▶); (h) Matthews et al. (1996 ▶); (i) Zhao et al. (2009 ▶).

Acknowledgments

The Interdisciplinary Centre for Mathematical and Computational Modelling (Warsaw, Poland) provided computational facilities.

supplementary crystallographic information

Comment

Our report concerns 6-bromo-2-(methylthio)benzo[d]thiazole (Fig.1). Its structure is essentially planar with dihedral angle between conjugated thiazole and benzene rings equal to 1.0 (1)°. Random deviation from 5-membered ring plane is 0.0019 Å. This is very similar to previously investigated systems containing benzothiazole moiety (Karolak-Wojciechowska et al., 2007).

There are four C—S bonds present in the molecule, which are formally single. However, except for C8—S2 [1.805 (3) Å ; reference bond length for single C—S bond used for HOMA is 1.807 Å, Krygowski & Cyrański (2001)], three other bonds are shorter [C7—S2 1.744 (3) Å, C7—S1 1.760 (3) Å, C3—S1 1.730 (3) Å, Fig 1]. This results from π···π conjugation and leads to higher cyclic delocalization in the thiazole ring. There are no hydrogen bonds present, but a short contact of 3.6133 (9) Å between bromine and sulfur atoms is observed (Fig. 2).

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.

Experimental

To a 5.01 g (0.025 mol) of 2-(methylthio)benzo[d]thiazole suspended in 50 ml of methanol the 1.5 ml of pure Br2 was added dropwise in portions (5 drops every 20 min). Since the beginning of the reaction the solution was extensively stirred for 8 h, and then obtained precipitate (4.67 g, 93%) was separated from reaction mixture and washed with ice cold methanol (3 portions of 50 ml). White solid residue was crystallized from absolute ethanol. Melting point 98-101°C. Single crystals were obtained immediately after slow evaporation of ethanol.

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.).