2-Methylthiazole

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Nitrogen and Sulfur

Nuclear Quadrupole Coupling Constants


in 2-Methylthiazole


 







 
Assuming Cs symmetry for 2-methylthiazole, one methyl CH bond lies in the plane of the thiazole ring.  Calculation of the nitrogen and sulfur nqcc's was made here on B3PW91/6-31G(2d,2pd) optimized molecular structures corresponding to each of two possible orientations of the methyl group, the in-plane CH bond being cis or trans with respect to the nitrogen atom.  These calculated nitrogen nqcc's are compared in Tables 1 and 2 with the experimental nqcc's of Grabow et al. [1]. Calculated sulfur nqcc's are given in Tables 3 and 4. Calculated nitrogen nqcc's in the 33S isotopomer are given in Table 5.  Structure parameters are compared in Table 6. Atomic coordinates for the lower energy cis conformer are given in Table 7. Rotational constants are compared in Table 8.
Molecular energy:  Ecis < Etrans by 0.22 kcal/mol calculated at the B3PW91/6-31G(2d,2pd) level of theory, 0.12 kcal/mol at B3PW91/ 6-311+G(df,pd),  0.15 kcal/mol at B3LYP/6-311G(3df,3p), and 0.09 kcal/mol at B3LYP/TZV+(3df,3p).
 
In Tables 1 and 5, subscripts a,b,c refer to the principal axes of the inertia tensor, subscripts x,y,z to the principal axes of the nqcc tensor.  The nqcc y-axis is chosen coincident with the inertia c-axis, these are perpendicular to the plane of the molecule.  Ø (degrees) is the angle between its subscripted parameters. ETA = (Xxx - Xyy)/Xzz.  RSD is the residual standard deviation of calibration of the model for calculation of the nqcc's.
 
 
   






Table 1.  Nitrogen nqcc's in 2-Methylthiazole-32S in the cis conformer (MHz).  Calculation was made on the B3PW91/6-31G(2d,2pd) ropt structure.
   









Calc.
Expt. [1]
   





14N Xaa 0.449 0.5239(15) *
Xbb - 2.859 - 2.9134
Xcc 2.410 2.3895
|Xab| 2.338 2.2791(137)
 
  RMS 0.055 (2.8 %)
RSD 0.030 (1.3 %)
 
Xxx 1.659 1.660(11)
Xyy 2.410 2.390(2)
Xzz - 4.069 - 4.0049(11)
ETA - 0.184
Øz,a 27.37 26.49(10)
Øa,bi 27.42
Øz,bi**   0.05
 
   
* Calculated here from X+ = - 0.5239(15) and X - = - 5.3030(25) MHz [1].
** The z-axis makes an angle of 0.05o with the bisector ( 'bi' ) of the CNC angle.
 
 
   






Table 2.  Nitrogen nqcc's in 2-Methylthiazole-32S in the trans conformer (MHz).  Calculation was made on the B3PW91/6-31G(2d,2pd) ropt structure.
   









Calc.
Expt. [1]
   





14N Xaa 0.517 0.5239(15)
Xbb - 2.852 - 2.9134
Xcc 2.334 2.3895
|Xab| 2.307 2.2791(137)
 
  RMS 0.049 (2.5 %)
RSD 0.030 (1.3 %)
 
Xxx 1.690 1.660(11)
Xyy 2.334 2.390(2)
Xzz - 4.024 - 4.0049(11)
ETA - 0.160
Øz,a 26.93 26.49(10)
Øa,bi 27.33
Øz,bi   0.40
 
 
 
   






Table 3.  33S nqcc's in 2-Methylthiazole in the cis conformer (MHz).  Calculation was made on the B3PW91/6-31G(2d,2pd) ropt structure.
Calc. [a] B3LYP/6-311G(3df,3p) Model.
Calc. [b] B3LYP/TZV+(3df,3p) Model.
   







Calc. [a]
Calc. [b]
Expt.
   





Xaa - 26.57 - 26.71
Xbb   5.51   5.59
Xcc 21.06 21.12
|Xab|   2.84   2.93
 
RSD 0.39 (1.7 %) 0.35 (1.5 %)
 
Xxx   5.76   5.85
Xyy 21.06 21.12
Xzz - 26.82 - 26.97
ETA 0.570 0.566
Øx,a 84.98 84.85
Øa,bi 83.59 83.59
Øx,bi*   1.38   1.26
 
 
* The x-axis makes an angle of 1.38o / 1.26o with the bisector ( 'bi' ) of the CSC angle.
 
 
   






Table 4.  33S nqcc's in 2-Methylthiazole in the trans conformer (MHz).  Calculation was made on the B3PW91/6-31G(2d,2pd) ropt structure.
Calc. [a] B3LYP/6-311G(3df,3p) Model.
Calc. [b] B3LYP/TZV+(3df,3p) Model.
   







Calc. [a]
Calc. [b]
Expt.
   





Xaa - 25.94 - 26.08
Xbb   5.94   6.01
Xcc 20.00 20.07
|Xab|   3.04   3.15
 
RSD 0.39 (1.7 %) 0.35 (1.5 %)
 
Xxx   6.23   6.32
Xyy 20.00 20.07
Xzz - 26.23 - 26.39
ETA 0.525 0.521
Øx,a 84.60 84.45
Øa,bi 83.41 83.41
Øx,bi*   1.19   1.04
 
 
* The x-axis makes an angle of 1.19o / 1.04o with the bisector ( 'bi' ) of the CSC angle.
 
 
   






Table 5.  14N nqcc's in 2-Methylthiazole-33S in the cis and trans conformer (MHz).  Calculation was made on the B3PW91/6-31G(2d,2pd) ropt structure.
   







Calc/cis
Calc/trans
Expt.
   





Xaa 0.422 0.492
Xbb - 2.832 - 2.826
Xcc 2.410 2.334
|Xab| 2.357 2.326
 
RSD 0.030 (1.3 %) 0.030 (1.3 %)
 
 
 
Table 6.   2-Methylthiazole.  Structure parameters, ropt (Å and degrees).
 
  cis  trans
S(1)C(2) 1.7480 1.7436
C(2)N(3) 1.3004 1.3011
N(3)C(4) 1.3704 1.3681
C(4)C(5) 1.3609 1.3626
C(5)S(1) 1.7212 1.7193
C(4)H(4) 1.0818 1.0819
C(5)H(5) 1.0782 1.0780
C(2)C 1.4926 1.4938
CH(7) 1.0888 1.0892
CH(8,9) 1.0922 1.0921
C(5)S(1)C(2)   89.48   89.54
S(1)C(2)N(3) 113.77 113.91
C(2)N(3)C(4) 111.27 111.11
N(3)C(4)C(5) 116.15 116.23
C(4)C(5)S(1) 109.33 119.20
C(4)C(5)H(5) 129.17 129.17
N(3)C(4)H(4) 119.09 119.10
S(1)C(2)C 121.87 121.70
C(2)CH(7) 108.50 111.74
C(2)CH(8,9) 111.54 110.13
 
 
Table 7.  2-Methylthiazole.  Atomic coordinates, ropt.  32S isotopomer, cis conformer.
  a (Å)   b (Å)   b (Å)
S(1) - 0.2842 - 1.1631 0
C(2) 0.7923 0.2140 0
N(3) 0.1776 1.3599 0
C(4) - 1.1829 1.1942 0
C(5) - 1.6306 - 0.0909 0
H(4) - 1.8193 2.0690 0
H(5) - 2.6440 - 0.4591
0
C 2.2764 0.0542 0
H(7) 2.7304 1.0439 0
H(8,9) 2.6210 - 0.4908 ± 0.8816

Table 8.  2-Methylthiazole.  Rotational Constants, ropt (MHz).  32S species.
 
Calc/cis Calc/trans    Expt. [1]
A 5340.7  5348.0 5343.883(74)
B 3265.9  3270.7 3265.914(54)
C 2052.4  2055.4 2052.252(51)


 







 
1] J.-U.Grabow, H.Hartwig, N.Heineking, W.Jäger, H.Mäder, H.W.Nicolaisen, and W.Stahl, J.Mol.Struct. 612,349(2002).

 







 
Thiazole 4-Fluorothiazole 5-Fluorothiazole
2-Fluorothiazole 4-Methylthiazole 5-Methylthiazole
1,2,4-Thiadiazole 1,2,5-Thiadiazole 1,3,4-Thiadiazole
Pyrazole Imidazole Oxazole
 

 








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Molecules/Nitrogen
Molecules/Sulfur
 

 













2MeThiazole.html






Last Modified 2 Oct 2004