Pyrazole


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Nitrogen


Nuclear Quadrupole Coupling Constants


in Pyrazole


 








 








 







Nitrogen nqcc's in pyrazole were first measured by Blackman et al. [1,2].  Nygaard et al. [3] determined a complete substitution molecular structure, and confirmed the nqcc's of Blackman, et al.  Sutter, et al. [4] subsequently remeasured the nqcc's to a higher degree of experimental accuracy.  A semi-experimental equilibrium structure reSE was derived by Császár et al. [5].

 








Calculation of the nqcc's was made here on the rs and reSE molecular structures, and on an ropt structure given by B3LYP/cc-pVTZ optimization.  In Tables 1 - 4, these calculated nqcc's are compared with the experimental nqcc's of Sutter et al. for pyrazole and 1-D-pyrazole.

 








In Tables 1 - 4, 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.  Ø (degrees) is the angle between its subscripted parameters.  ETA = (Xxx - Xyy)/Xzz.

 








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

 








 








 










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












Calc /rs
Calc /reSE
Calc /ropt
Expt. [4]
 










Xaa
1.435
1.334
1.390
1.391(6)

Xbb
1.642
1.672
1.647
1.662(6)

Xcc - 3.077 -
 3.006
 -
 3.037
 - 3.053(12)

|Xab|
0.735
0.706
0.712
0.730(21)












RMS
0.031 (1.5 %)
0.043 (2.1 %)
0.012 (0.6 %)



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














Xxx
0.797
0.777
0.795
0.791(36)

Xyy
2.281
2.229
2.242
2.277(29)

Xzz - 3.077 -
 3.006
 -
 3.037
 - 3.068(9)

ETA
0.482
0.483
0.477



Øx,a
40.98
38.28
39.88
39.74

Øa,NH
63.80
62.98
64.76



Øx,NH
22.82
24.70
24.88















 








 








 










Table 2.  14N (Pyridinic) nqcc's in Pyrazole (MHz).  Calculation was made on the rs,  reSE, and ropt structures.
 












Calc /rs
Calc /reSE
Calc /ropt
Expt. [4]
 










Xaa - 3.906 -
 4.020
 -
 3.913
 - 3.960(5)

Xbb
3.080
3.198
3.088
3.140(5)

Xcc
0.826
0.822
0.825
0.820(10)

|Xab|
2.042
1.852
2.080
1.943(6)












RMS
0.046 (1.8 %)
0.049 (1.8 %)
0.041 (1.5 %)



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














Xxx
3.633
3.645
3.659
3.621(4)

Xyy
0.826
0.822
0.825
0.853(10)

Xzz - 4.460 -
 4.467
 -
 4.484
 - 4.473(10)

ETA - 0.629 -
 0.632
 -
 0.632



Øz,a
15.15
13.58
15.36
14.35

Øa,bi
  2.56
  3.90
  2.19



Øz,bi *
17.72
17.48
17.55















 








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

 








 








 










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












Calc /rs
Calc /reSE
Calc /ropt
Expt. [4]
 










Xaa
0.908
0.947
0.975
0.957(7)

Xbb
2.169
2.060
2.062
2.123(7)

Xcc - 3.077 -
 3.006
 -
 3.037
 - 3.082(6)

|Xab|
0.392
0.466
0.478
0.466(14)












RMS
0.039 (1.9 %)
0.057 (2.8 %)
0.045 (2.2 %)



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















 








 








 










Table 4.  14N (Pyridinic) nqcc's in 1-D-Pyrazole (MHz).  Calculation was made on the rs,  reSE, and ropt structures.
 












Calc /rs
Calc /reSE
Calc /ropt
Expt. [4]
 










Xaa - 0.869 -
 0.456
 -
 0.386
 - 0.507(9)

Xbb
0.043 -
 0.366
 -
 0.440
 - 0.378(9)

Xcc
0.826
0.822
0.826
0.885(9)

|Xab|
4.021
4.056
4.072
4.046(5)












RMS
0.322 (55 %)
0.047 (8.0 %)
0.086 (14.5 %)



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















 







 
 



Table 5. Molecular structure parameters, rs [3], reSE [5] and ropt (Å and degrees).





 
     rs   reSE   ropt






N(1)H(1) 0.9978(4)1.0014(4)
 1.0043

N(1)N(2) 1.3488(6)1.3431(6)
 1.3445

N(2)C(3) 1.3306(5)1.3286(7)
 1.3272

C(3)C(4) 1.4162(2)1.4093(6)
 1.4096

C(4)C(5) 1.3724(6)1.3771(8)
 1.3762

C(5)N(1) 1.3591(1)1.3523(6)
 1.3538

C(3)H(3) 1.0784(4)1.0755(4)
 1.0774

C(4)H(4) 1.0756(5)1.0736(4)
 1.0752

C(5)H(5) 1.0774(5)1.0740(5)
 1.0760

N(1)N(2)C(3) 104.07(1)104.18(3)
 104.25

N(2)C(3)C(4) 111.94(3)111.90(5)
 111.88

C(3)C(4)C(5) 104.50(2)104.46(4)
 104.53

C(4)C(5)N(1) 106.42(2)106.23(4)
 106.21

C(5)N(1)N(2) 113.07(3)113.24(5)
 113.12

N(2)C(3)H(3) 119.31(4)119.49(14)
 119.66

C(3)C(4)H(4) 127.90(5)128.32(13)
 128.22

N(1)C(5)H(5) 121.47(4)121.84(11)
 121.97

N(2)N(1)H(1) 118.40(3)118.97(11)
 119.08



 








 








[1] G.L.Blackman, R.D.Brown, and F.R.Burden, J.Mol.Spectrosc. 36,528(1965).

[2] G.L.Blackman, R.D.Brown, F.R.Burden, and A.Mishra, J.Mol.Struct. 9,465(1971).

[3] L.Nygaard, D.Christen, J.T.Nielsen, E.J.Pedersen, O.Snerling, E.Vestergaard, and G.O.Sørensen, J.Mol.Struct. 22,401(1974).

[4] O.Böttcher and D.H.Sutter, Z.Naturforsch. 45a,1248(1990); M.Stolze and D.H.Sutter, Z.Naturforsch. 42a,49(1987).

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

 








 








Pyrrole Imidazole Oxazole



Pyridine Isoxazole Thiazole



 








 








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Molecules/Nitrogen




 








 













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Last Modified 27 Oct 2014