C4H6N2































 























Nitrogen


Nuclear Quadrupole Coupling Constants

in 4-Methylimidazole

 








 
 N-Methylimidazole 2-Methylimidazole 5-Methylimidazole






















14N nuclear quadrupole coupling constants in 4-methylimidazole were determined by Gougoula, et al. [1].











Calculation of the 14N nuclear quadrupole coupling constants was made here on a B3LYP/cc-pVTZ  opimized molecular structure, and on a heavy atom rs structure [1] with hydrogen parameters determined by B3LYP/cc-pVTZ partial optimization.

 








Calculated and experimental nqcc's are compared in Tables 1 and 2.  Structure parameters in Z-matrix format are given in Table 3, rotational constants are compared in Table 4.


 








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.  ETA = (Xxx - Xyy)/Xzz.  Ø (degrees) is angle between its subscripted parameters.  RMS is the root mean square difference between calculated and experimental diagonal nqcc's.  RSD is the calibration residual standard deviation of the B3PW91/6-311+G(df,pd) model for calculation of the nitrogen efg's/nqcc's. 


 








 








   







Table 1.  Pyrrolic 14N(1) nqcc's in 4-Methylimidazole (MHz).  Calculation was made on  the ropt = B3LYP/cc-pVTZ optimized structure, and on the heavy atom rs structure.
   









Calc /ropt
Calc /rs
Expt [1]
   







Xaa
1.425
1.435
1.4065(49)

Xbb - Xcc
3.778
3.685
3.8163(88)

Xbb
1.176
1.125
1.2049 *

Xcc -
 2.601
 -
 2.560
 -
 2.6114 *

Xab
0.119
0.093












RMS
0.020 (1.2 %)
0.057 (3.3 %)



RSD
0.030 (1.3 %)
0.030 (1.3 %)



 







Xxx
1.129
1.099



Xyy
1.472
1.461



Xzz -
 2.601
 -
 2.560



ETA
0.132
0.141



Øz,c
 zero
 zero



 








 








* Calculated here from experimental Xaa and Xbb - Xcc

 








 








   







Table 2.  Pyridinic 14N(3) nqcc's in 4-Methylimidazole (MHz).  Calculation was made on the ropt = B3LYP/cc-pVTZ optimized structure, and on the heavy atom rs structure.
   









Calc /ropt
Calc /rs
Expt [1]
   







Xaa
0.994
1.069
0.9529(55)

Xbb - Xcc -
 5.195
 -
 5.465
 -
 5.1394(10)

Xbb -
 3.094
 -
 3.267
 -
 3.0462 *

Xcc
2.100
2.198
2.0933 *

Xab -
 2.095
 -
 1.948












RMS
0.037 (1.8 %)
0.157 (7.7 %)



RSD
0.030 (1.3 %)
0.030 (1.3 %)



 







Xxx
1.877
1.816



Xyy
2.100
2.198



Xzz -
 3.977
 -
 4.014



ETA
0.0562
0.0949



Øz,bi**







 








 








* Calculated here from experimental Xaa and Xbb - Xcc

** "bi" is bisector of C(2)N(3)C(4) angle.

 








 


Table 3.  4-Methylimidazole:  Structure parameters,  ropt = B3LYP/cc-pVTZ optimized structure, and rs = heavy atom substitution structure. (Å and degrees). 





 N
 C,1,B1
 N,2,B2,1,A1
 C,3,B3,2,A2,1,D1,0
 C,4,B4,3,A3,2,D2,0
 H,1,B5,2,A4,3,D3,0
 H,2,B6,1,A5,5,D4,0
 H,5,B7,4,A6,3,D5,0
 C,4,B8,3,A7,2,D6,0
 H,9,B9,4,A8,3,D7,0
 H,9,B10,4,A9,3,D8,0
 H,9,B11,4,A10,3,D9,0


      ropt       rs




 B1=1.35962633
 B2=1.3098159
 B3=1.37882845
 B4=1.36943069
 B5=1.00445447
 B6=1.07757105
 B7=1.07514121
 B8=1.49156554
 B9=1.0895763
 B10=1.09150567
 B11=1.09150567
 A1=111.5509812
 A2=106.01270374
 A3=109.69468042
 A4=126.59023736
 A5=122.48959325
 A6=132.12618112
 A7=121.53762217
 A8=111.20362717
 A9=110.8774398
 A10=110.8774398
 D1=0.
 D2=0.
 D3=180.
 D4=180.
 D5=180.
 D6=180.
 D7=180.
 D8=-59.45568649
 D9=59.45568649
 B1=1.36240973
B2=1.30405213
B3=1.34644841
B4=1.39394531
B5=1.00422021
B6=1.07787749
B7=1.07413000
B8=1.49752065
B9=1.08906490
B10=1.09174012
B11=1.09174012
A1=112.22173701
A2=106.68247256
A3=110.66795215
A4=126.79362204
A5=122.07132955
A6=133.12815744
A7=124.07123000
A8= 110.77343025
A9=111.06843406
A10=111.06843406
D1=0.
D2=0.
D3=180.
D4=180.
D5=180.
D6=180.
D7=180.
D8=-59.55344351
D9=59.55344351







 







 






Table 4.  4-Methylimidazole: Rotational Constants (MHz).

 





 Calc /ropt  Calc /rs     Expt [1]

 




 A
     9048.
   9010.
 8966.7590(10)

 B
     3519.
   3511.
 3508.41729(51)

 C
     2573.
   2566
 2561.52449(47)









 








 








[1] E.Gougoula, C.Medcraft, J.Heitkämper, and N.Walker, Abstract MI01, 74th ISMS, Champaign-Urbana, Illinois, 2019;  J.Chem.Phys. 151,144301(2019).

 








 








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Last Modified 9 Oct 2019