5-CH3-C3H2NO




 






 








Nitrogen


Nuclear Quadrupole Coupling Constants


in 5-Methyloxazole


 








 








 








Assuming Cs symmetry, the in-plane methyl hydrogen in 5-methyloxazole may be cis or trans with respect to the ring oxygen.  Calculation of the nitrogen nqcc's was made here on cis and trans conformer structures given by B3PW91/6-31G(2d,2pd) optimization.  These are compared with the experimental nqcc's of Fliege [1] in Tables 1 and 2.

 








For calculation at the B3PW91/6-31G(2d,2pd) level of theory, Etrans < Ecis by 1.1 kcal/mol. At the B3PW91/6-311+G(df,pd)  level, Etrans < Ecis by 1.2 kcal/mol. Structure parameters and atomic coordinates are given in Tables 3 and 4 for the lower energy trans conformer.

 








In Tables 1 and 2, subscripts a,b,c refer to the principal axes of the inertia tensor; 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 molecular plane.  (degrees) is the angle between its subscripted parameters.  ETA = (Xxx - Xyy)/Xzz


RMS is the root mean square difference between calculated and experimental diagonal nqcc's (percentage of the average of the magnitudes of the experimental nqcc's).  RSD is the calibration residual standard deviation for the B3PW91/6-311+G(df,pd) model for calculation of the nqcc's.

 








 








   







Table 1.  Nitrogen nqcc's in 5-Methyloxazole, trans (MHz).  Calculation was made on the B3PW91/6-31G(2d,2pd) ropt structure.

 









Calc.
Expt. [1]
   







14N Xaa - 2.304 - 2.215(13)


Xbb - 0.158 - 0.201(12)


Xcc
2.462
2.416(12)


|Xab|
2.703
2.860

 







RMS
0.063 (3.9 %)




RSD
0.030 (1.3 %)



 






  Xxx
1.677
1.824


Xyy
2.462
2.416


Xzz - 4.140 - 4.240


ETA
0.190




z,a
34.17
35.3


a,bi
29.87




z,bi *
  4.30



 







 








* The z-axis makes an angle of 4.30o with the external bisector ( 'bi' ) of the C(2)N(3)C(4) angle, and tilts toward C(4).

 








 








   







Table 2.  Nitrogen nqcc's in 5-Methyloxazole, cis (MHz).  Calculation was made on the B3PW91/6-31G(2d,2pd) ropt structure.
   










Calc.
Expt. [1]
   







14N Xaa - 2.344 - 2.215(13)


Xbb - 0.148 - 0.201(12)


Xcc
2.492
2.416(12)


|Xab|
2.708
2.860


 






RMS
0.092 (5.7 %)




RSD
0.030 (1.3 %)



 







 







 
 


Table 3.  5-Methyloxazole, trans.  Molecular structure parameters, ropt ( and degrees).
 




O(1)C(2) 1.3511


C(2)N(3) 1.2895


N(3)C(4) 1.3865


C(4)C(5) 1.3565


C(5)O(1) 1.3680


C(2)H(2) 1.0781


C(4)H(4) 1.0780


C(5)O(1)C(2) 104.58


O(1)C(2)N(3) 114.89


C(2)N(3)C(4) 103.74


N(3)C(4)C(5) 109.74


C(4)C(5)O(1) 107.05


O(1)C(2)H(2) 116.49


N(3)C(4)H(4) 121.89






  Methyl






C(5)C(6) 1.4803


C(6)H(7) 1.0894


C(6)H(8,9) 1.0929


C(5)C(6)H(7) 109.64


C(5)C(6)H(8,9) 111.41


H(8)C(6)H(9) 107.62



 








 
















Table 4.  5-Methyloxazole, trans.  Atomic coordinates, ropt.

 









 a ()
 b ()
 c ()









O(1) - 0.0228 - 1.0507


C(2) - 1.3173 - 0.6639


N(3) - 1.5024
0.6122


C(4) - 0.2168
1.1316


C(5)
0.6862
0.1193


H(2) - 2.0543 - 1.4508


H(4) - 0.0317
2.1935


C(6)
2.1639
0.0332


H(7)
2.5892
1.0361


H(8.9)
2.5328 - 0.4964 0.8820


 








 









[1] E.R.L.Fliege, Z.Naturforsch. 45a,911(1990); E.Fliege, H.Dreizler, M.Meyer, K.Igbal, and J.Sheridan, Z.Naturforsch. 41a,623(1981).

 









 








Oxazole 2-Methyloxazole 4-Methyloxazole

Thiazole 4-Methylthiazole 5-Methylthiazole

 








 








Table of Contents





Molecules/Nitrogen




 








 













5MeOxazole.html






Last Modified 8 Nov 2003