organic compounds
6-Bromo-2-methylsulfanyl-1,3-benzothiazole
aUniversity of Warsaw, Faculty of Chemistry, Pasteura 1, 02-093 Warsaw, Poland, and bMedical University of Warsaw, Faculty of Medicine, Oczki 3, 02-007 Warsaw, Poland
*Correspondence e-mail: miked@chem.uw.edu.pl
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 (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
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Data collection: CrysAlis CCD (Oxford Diffraction, 2009); cell 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).
Supporting information
https://doi.org/10.1107/S160053681105015X/gk2424sup1.cif
contains datablocks I, global. DOI:Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S160053681105015X/gk2424Isup2.hkl
Supporting information file. DOI: https://doi.org/10.1107/S160053681105015X/gk2424Isup3.cml
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.).
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).
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) 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.
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).
Data collection: CrysAlis CCD (Oxford Diffraction, 2009); cell
CrysAlis RED (Oxford Diffraction, 2009); data reduction: CrysAlis RED (Oxford Diffraction, 2009); 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).Fig. 1. The molecular structure of the title compound showing displacement ellipsoids at the 50% probability level. | |
Fig. 2. Short contacts between bromine and sulfur atoms; view along the b axis. Intermolecular Br···S are shown with dashed lines. |
C8H6BrNS2 | F(000) = 256 |
Mr = 260.18 | Dx = 1.937 Mg m−3 |
Monoclinic, P21 | Melting point = 371–374 K |
Hall symbol: P 2yb | Mo Kα radiation, λ = 0.71073 Å |
a = 9.7843 (4) Å | Cell parameters from 2764 reflections |
b = 3.9514 (2) Å | θ = 2.9–28.5° |
c = 11.6076 (5) Å | µ = 5.01 mm−1 |
β = 96.353 (4)° | T = 100 K |
V = 446.01 (3) Å3 | Needle, colourless |
Z = 2 | 0.4 × 0.15 × 0.1 mm |
Oxford Diffraction Xcalibur S diffractometer | 1227 independent reflections |
Radiation source: fine-focus sealed tube | 1125 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.024 |
Detector resolution: 8.6479 pixels mm-1 | θmax = 25.0°, θmin = 2.9° |
phi and ω scans | h = −11→11 |
Absorption correction: multi-scan (CrysAlis RED; Oxford Diffraction, 2009) | k = −4→3 |
Tmin = 0.422, Tmax = 0.606 | l = −13→13 |
3437 measured reflections |
Refinement on F2 | Secondary atom site location: difference Fourier map |
Least-squares matrix: full | Hydrogen site location: inferred from neighbouring sites |
R[F2 > 2σ(F2)] = 0.017 | H-atom parameters constrained |
wR(F2) = 0.033 | w = 1/[σ2(Fo2) + (0.0143P)2] where P = (Fo2 + 2Fc2)/3 |
S = 0.99 | (Δ/σ)max = 0.002 |
1227 reflections | Δρmax = 0.36 e Å−3 |
110 parameters | Δρmin = −0.22 e Å−3 |
1 restraint | Absolute structure: Flack (1983), 315 Friedel pairs |
Primary atom site location: structure-invariant direct methods | Absolute structure parameter: 0.005 (9) |
C8H6BrNS2 | V = 446.01 (3) Å3 |
Mr = 260.18 | Z = 2 |
Monoclinic, P21 | Mo Kα radiation |
a = 9.7843 (4) Å | µ = 5.01 mm−1 |
b = 3.9514 (2) Å | T = 100 K |
c = 11.6076 (5) Å | 0.4 × 0.15 × 0.1 mm |
β = 96.353 (4)° |
Oxford Diffraction Xcalibur S diffractometer | 1227 independent reflections |
Absorption correction: multi-scan (CrysAlis RED; Oxford Diffraction, 2009) | 1125 reflections with I > 2σ(I) |
Tmin = 0.422, Tmax = 0.606 | Rint = 0.024 |
3437 measured reflections |
R[F2 > 2σ(F2)] = 0.017 | H-atom parameters constrained |
wR(F2) = 0.033 | Δρmax = 0.36 e Å−3 |
S = 0.99 | Δρmin = −0.22 e Å−3 |
1227 reflections | Absolute structure: Flack (1983), 315 Friedel pairs |
110 parameters | Absolute structure parameter: 0.005 (9) |
1 restraint |
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. |
Refinement. Refinement of F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > σ(F2) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F2 are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger. |
x | y | z | Uiso*/Ueq | ||
C1 | 0.7671 (3) | 0.6254 (7) | 0.9919 (3) | 0.0141 (7) | |
C2 | 0.8559 (3) | 0.5366 (12) | 0.9147 (2) | 0.0123 (6) | |
C3 | 0.8181 (3) | 0.6157 (7) | 0.7984 (3) | 0.0121 (7) | |
C4 | 0.6939 (3) | 0.7815 (8) | 0.7626 (3) | 0.0121 (7) | |
C5 | 0.6060 (3) | 0.8712 (7) | 0.8439 (3) | 0.0137 (7) | |
C6 | 0.6430 (3) | 0.7938 (8) | 0.9590 (3) | 0.0135 (7) | |
C7 | 0.7722 (3) | 0.7402 (8) | 0.5934 (3) | 0.0127 (7) | |
C8 | 0.6257 (3) | 0.9551 (10) | 0.3940 (3) | 0.0192 (8) | |
N1 | 0.6702 (3) | 0.8486 (6) | 0.6440 (2) | 0.0131 (6) | |
S1 | 0.90775 (7) | 0.5420 (3) | 0.68048 (6) | 0.01509 (19) | |
S2 | 0.79094 (8) | 0.7776 (2) | 0.44632 (7) | 0.01761 (19) | |
Br1 | 0.81246 (3) | 0.50973 (9) | 1.15124 (2) | 0.01701 (9) | |
H2 | 0.9403 | 0.4254 | 0.9390 | 0.015* | |
H5 | 0.5218 | 0.9841 | 0.8205 | 0.016* | |
H6 | 0.5845 | 0.8546 | 1.0158 | 0.016* | |
H8A | 0.6084 | 1.1556 | 0.4399 | 0.029* | |
H8B | 0.5537 | 0.7867 | 0.4011 | 0.029* | |
H8C | 0.6254 | 1.0196 | 0.3124 | 0.029* |
U11 | U22 | U33 | U12 | U13 | U23 | |
C1 | 0.0180 (18) | 0.0130 (17) | 0.0109 (16) | −0.0034 (13) | −0.0003 (14) | 0.0000 (13) |
C2 | 0.0133 (13) | 0.0076 (16) | 0.0157 (14) | −0.0013 (16) | 0.0000 (10) | 0.0028 (16) |
C3 | 0.0103 (16) | 0.0095 (15) | 0.0169 (16) | −0.0012 (12) | 0.0029 (13) | −0.0044 (12) |
C4 | 0.0120 (17) | 0.0099 (16) | 0.0144 (17) | −0.0050 (14) | 0.0012 (13) | −0.0032 (14) |
C5 | 0.0122 (17) | 0.0110 (15) | 0.0178 (18) | 0.0005 (12) | 0.0013 (13) | −0.0010 (13) |
C6 | 0.0134 (17) | 0.0123 (16) | 0.0157 (18) | −0.0017 (14) | 0.0051 (13) | −0.0050 (14) |
C7 | 0.0137 (17) | 0.0090 (15) | 0.0150 (17) | −0.0048 (14) | −0.0001 (14) | −0.0006 (14) |
C8 | 0.0213 (17) | 0.019 (2) | 0.0171 (16) | −0.0014 (17) | −0.0006 (13) | 0.0025 (17) |
N1 | 0.0132 (15) | 0.0136 (13) | 0.0122 (14) | −0.0018 (11) | 0.0011 (11) | 0.0012 (11) |
S1 | 0.0140 (4) | 0.0166 (5) | 0.0149 (4) | 0.0027 (5) | 0.0027 (3) | −0.0012 (5) |
S2 | 0.0190 (5) | 0.0197 (4) | 0.0149 (4) | 0.0020 (4) | 0.0049 (3) | 0.0010 (4) |
Br1 | 0.02064 (16) | 0.01663 (14) | 0.01365 (15) | 0.0003 (2) | 0.00146 (11) | 0.0021 (2) |
S1—C3 | 1.730 (3) | C6—H6 | 0.9500 |
S1—C7 | 1.760 (3) | C3—C4 | 1.402 (4) |
N1—C7 | 1.286 (4) | C4—C5 | 1.391 (4) |
N1—C4 | 1.396 (4) | C5—H5 | 0.9500 |
C2—C1 | 1.362 (4) | C7—S2 | 1.744 (3) |
C2—C3 | 1.395 (4) | S2—C8 | 1.805 (3) |
C2—H2 | 0.9500 | C8—H8A | 0.9800 |
C1—C6 | 1.400 (4) | C8—H8B | 0.9800 |
C1—Br1 | 1.909 (3) | C8—H8C | 0.9800 |
C6—C5 | 1.379 (4) | ||
C3—S1—C7 | 87.90 (14) | C5—C4—C3 | 119.9 (3) |
C7—N1—C4 | 109.5 (3) | N1—C4—C3 | 115.2 (3) |
C1—C2—C3 | 117.3 (3) | C6—C5—C4 | 119.0 (3) |
C1—C2—H2 | 121.3 | C6—C5—H5 | 120.5 |
C3—C2—H2 | 121.3 | C4—C5—H5 | 120.5 |
C2—C1—C6 | 122.7 (3) | N1—C7—S2 | 126.2 (2) |
C2—C1—Br1 | 118.6 (2) | N1—C7—S1 | 117.4 (2) |
C6—C1—Br1 | 118.7 (2) | S2—C7—S1 | 116.46 (18) |
C5—C6—C1 | 119.8 (3) | C7—S2—C8 | 100.09 (15) |
C5—C6—H6 | 120.1 | S2—C8—H8A | 109.5 |
C1—C6—H6 | 120.1 | S2—C8—H8B | 109.5 |
C2—C3—C4 | 121.3 (3) | H8A—C8—H8B | 109.5 |
C2—C3—S1 | 128.6 (2) | S2—C8—H8C | 109.5 |
C4—C3—S1 | 110.0 (2) | H8A—C8—H8C | 109.5 |
C5—C4—N1 | 124.9 (3) | H8B—C8—H8C | 109.5 |
C3—C2—C1—C6 | −0.9 (5) | C2—C3—C4—N1 | 179.2 (3) |
C3—C2—C1—Br1 | 178.1 (3) | S1—C3—C4—N1 | 0.1 (3) |
C2—C1—C6—C5 | 1.0 (5) | C1—C6—C5—C4 | −0.4 (4) |
Br1—C1—C6—C5 | −178.1 (2) | N1—C4—C5—C6 | −179.0 (3) |
C1—C2—C3—C4 | 0.3 (5) | C3—C4—C5—C6 | −0.1 (4) |
C1—C2—C3—S1 | 179.3 (3) | C4—N1—C7—S2 | −178.1 (2) |
C7—S1—C3—C2 | −178.8 (4) | C4—N1—C7—S1 | 0.6 (3) |
C7—S1—C3—C4 | 0.2 (2) | C3—S1—C7—N1 | −0.5 (3) |
C7—N1—C4—C5 | 178.5 (3) | C3—S1—C7—S2 | 178.36 (19) |
C7—N1—C4—C3 | −0.4 (4) | N1—C7—S2—C8 | −6.0 (3) |
C2—C3—C4—C5 | 0.2 (5) | S1—C7—S2—C8 | 175.2 (2) |
S1—C3—C4—C5 | −178.9 (2) |
Experimental details
Crystal data | |
Chemical formula | C8H6BrNS2 |
Mr | 260.18 |
Crystal system, space group | Monoclinic, P21 |
Temperature (K) | 100 |
a, b, c (Å) | 9.7843 (4), 3.9514 (2), 11.6076 (5) |
β (°) | 96.353 (4) |
V (Å3) | 446.01 (3) |
Z | 2 |
Radiation type | Mo Kα |
µ (mm−1) | 5.01 |
Crystal size (mm) | 0.4 × 0.15 × 0.1 |
Data collection | |
Diffractometer | Oxford Diffraction Xcalibur S |
Absorption correction | Multi-scan (CrysAlis RED; Oxford Diffraction, 2009) |
Tmin, Tmax | 0.422, 0.606 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 3437, 1227, 1125 |
Rint | 0.024 |
(sin θ/λ)max (Å−1) | 0.596 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.017, 0.033, 0.99 |
No. of reflections | 1227 |
No. of parameters | 110 |
No. of restraints | 1 |
H-atom treatment | H-atom parameters constrained |
Δρmax, Δρmin (e Å−3) | 0.36, −0.22 |
Absolute structure | Flack (1983), 315 Friedel pairs |
Absolute structure parameter | 0.005 (9) |
Computer programs: CrysAlis CCD (Oxford Diffraction, 2009), CrysAlis RED (Oxford Diffraction, 2009), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), Mercury (Macrae et al., 2006), publCIF (Westrip, 2010).
BT = benzothiazole; MePyr = methylpyridine. |
refcode | R = | HOMA (total) | HOMA (thiazole) | HOMA (benzene) |
This work | H | 0.82 | 0.69 | 0.95 |
DIDBAUa | -C(Ph)=N-NH-C(O)-NH2 | 0.85 | 0.73 | 0.99 |
HUFSILb | -CH2-O-CH2-CH2-S-BT | 0.83 | 0.69 | 0.98 |
HUYYIJc | -CH2-CH2-CH2-S-BT | 0.84 | 0.70 | 0.98 |
MACMOTd | -CH2-S-BT | 0.85 | 0.72 | 0.97 |
-CH2-S-BT | 0.85 | 0.71 | 0.98 | |
MACMOT01e | -CH2-S-BT | 0.85 | 0.70 | 0.98 |
-CH2-S-BT | 0.85 | 0.71 | 0.97 | |
MOKJIGf | -C(O)-C(COOCH3)=N-O-CH3 | 0.83 | 0.70 | 0.96 |
PUFGEDg | -C(O)-Ph | 0.84 | 0.70 | 0.96 |
QOTQASh | -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 |
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). |
Acknowledgements
The Interdisciplinary Centre for Mathematical and Computational Modelling (Warsaw, Poland) provided computational facilities.
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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.