Pyrimidine






 






Nitrogen


Nuclear Quadrupole Coupling Constants


in Pyrimidine


 








 








Nitrogen nqcc's in pyrimidine were determined by Kisiel et al. [1], which authors also determined a heavy atom substitution structure.  A semi-experimental equilibrium structure, reSE, was derived by Császár et al. [2].


 









Calculation of the nitrogen nqcc's in pyrimidine were made on the rs and reSE structures, as well as an ropt structure given by B3P86/6-31G(3d,3p) optimization.  For the heavy atom substitution structure, the CH parameters used here are taken from the optimized structure.  These calculated nqcc's are compared with the experimental values [1] in Table 1.  Structure parameters are compared in Table 2.  In Table 3, atomic coordinates are given for the ropt structure.

 








In Table 1, 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.  Ř (degrees) is the angle between its subscripted parameters. ETA = (Xxx - Xyy)/Xzz.

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

 








 








   










Table 1. 14N(1,3) nqcc's in Pyrimidine (MHz).  Calculation was made on the rs, reSE, and ropt structures.
   












Calc /rs
Calc /reSE
Calc /ropt
Expt. [1]
   










Xaa -
3.070 -
3.109
- 3.106 - 3.1004(7)

Xbb -
0.286 -
0.255
- 0.258 - 0.2554(7)

Xcc
3.357
3.364

3.364
3.3558(7)

Xab ± 2.739 ± 2.721
± 2.718 ± 2.76(7)

 









RMS
0.025 (1.1 %)
0.007 (0.3 %)

0.006 (0.3 %)



RSD
0.030 (1.3 %)
0.030 (1.3 %)
0.030 (1.3 %)



 









Xxx
1.394
1.390

1.386
1.43(6)

Xyy
3.357
3.364

3.364
3.3558(7)

Xzz -
4.751 -
4.754
- 4.750 - 4.78(6)

ETA
0.413
0.415

0.416



Řz,a
31.53
31.16

31.17
31.4(3)

Řa,bi
31.5(2)
31.54

31.54
31.5(2)

Řz,bi*
  0
  0.38

  0.36
  0

 









   








* Angle between the z-axis and the bisector ( 'bi' ) of the CNC angle.

 








 













Table 3. Molecular structure parameters: rs [1], reSE [2], and B3P86/6-31G(3d,3p) ropt (Ĺ and degrees).
 





    rs
  reSE
  ropt 






C(2)N(3) 1.337(2) 1.3331(3)
1.3320

N(3)C(4) 1.332(3) 1.3349(6)
1.3328

C(4)C(5) 1.393(2) 1.3874(4)
1.3877

C(2)H(2)
1.0820(23)
1.0876

C(4)H(4)
1.0843(17)
1.0879

C(5)H(5)
1.0799(23)
1.0835

N(1)C(2)N(3) 127.2(3) 127.364(38)
127.38

C(2)N(3)C(4) 115.8(3) 115.712(21)
115.70

N(3)C(4)C(5) 122.4(3) 122.276(19)
122.40

C(4)C(5)C(6) 116.4(2) 116.661(36)
116.44

C(5)C(4)H(4)
121.24(20)
121.16


 








 








 




Table 4. Atomic coordinates, B3P86/6-31G(3d,3p) ropt
(More figures are shown than are significant.)
 







   a (Ĺ)
   b (Ĺ)







N(1,3) ± 1.193960 - 0.685056

C(2)
0.0 - 1.275471

C(4,6) ± 1.179635
0.647712

C(5)
0.0
1.378622

H(2)
0.0 - 2.363039

H(4,6) ± 2.148487
1.142540

H(5)
0.0
2.462154


 








 








[1] Z.Kisiel, L.Pszczólkowski, J.C.López, J.L.Alonso, A.Maris, and W.Caminati, J.Mol.Spectrosc. 195,332(1999).

[2] A.G.Császár, J.Demaison, and H.D.Rudolph, J.Phys.Chem. A, 119(9),1731(2015).

 









G.L.Blackman, R.D.Brown, and F.R.Burden, J.Mol.Spectrosc. 35,444(1970).  Xaa = -3.107(14), Xbb  = -0.223(16), and Xcc = 3.330(14) MHz.

 








 








Pyridine Pyrazine 1,3,5-Triazine

2-Fluoropyrimidine 2-Chloropyrimidine 2-Bromopyrimidine

 








 








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Molecules/Nitrogen




 








 













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Last Modified 30 Oct 2014