C4H6N2































 























Nitrogen


Nuclear Quadrupole Coupling Constants

in N-Methylimidazole

 








 
 4-Methylimidazole 2-Methylimidazole 5-Methylimidazole






















14N nuclear quadrupole coupling constants in N-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 N-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
1.720
1.639
1.7347(51)

Xbb - Xcc
3.535
3.186
3.6373(83)

Xbb
0.908
0.773
0.9513 *

Xcc -
 2.628
 -
 2.412
 -
 2.6860 *

Xab -
 0.079
 -
 0.076












RMS
0.043 (2.4 %)
0.196 (11. %)



RSD
0.030 (1.3 %)
0.030 (1.3 %)



 







Xxx
0.900
0.767



Xyy
1.728
1.645



Xzz -
 2.628
 -
 2.412



ETA
0.315
0.364



Øz,c
 zero
 zero



 








 








* Calculated here from experimental Xaa and Xbb - Xcc

 








 








   







Table 2.  Pyridinic 14N(3) nqcc's in N-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 -
 2.106
 -
 1.947
 -
 2.0837(52)

Xbb - Xcc -
 2.271
 -
 2.154
 -
 2.200(10)

Xbb -
 0.083
 -
 0.104
 -
 0.0582 *

Xcc
2.189
2.050
2.1419 *

Xab -
 2.770
 -
 2.012












RMS
0.033 (2.3 %)
0.083 (5.8 %)



RSD
0.030 (1.3 %)
0.030 (1.3 %)



 







Xxx
1.855
1.933



Xyy
2.189
2.050



Xzz -
 4.044
 -
 3.984



ETA
0.0826
0.0294



Øz,bi**







 








 








* Calculated here from experimental Xaa and Xbb - Xcc

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

 








 


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






   NOTE: ropt and rs Z-matrices are a litle different.

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


      ropt       rs




 B1=1.36274885
 B2=1.31152009
 B3=1.37203485
 B4=1.36851928
 B5=1.07825864
 B6=1.0768785
 B7=1.07557101
 B8=1.4493428
 B9=1.08785012
 B10=1.0904446
 B11=1.0904446
 A1=112.30015529
 A2=105.1292245
 A3=110.4746026
 A4=121.75813002
 A5=121.59827123
 A6=132.34886846
 A7=126.83893672
 A8=108.92955648
 A9=110.86250072
 A10=110.86250072
 D1=0.
 D2=0.
 D3=180.
 D4=180.
 D5=180.
 D6=180.
 D7=0.
 D8=119.43557872
 D9=-119.43557872
 B1=1.33920340
B2=1.33646353
B3=1.37510031
B4=1.37045965
B5=1.07749878
B6=1.07674629
B7=1.07491253
B8=1.45200011
B9=1.08757960
B10=1.08967587
B11=1.08967587
A1=112.06278702
A2=104.67247774
A3=108.29277018
A4=122.48751858
A5=121.71672531
A6=122.39244870
A7=127.42694736
A8=109.18348798
A9=110.58838339
A10=110.58838339
D1=0.00000000
D2=0.00000000
D3=180.00000000
D4=180.00000000
D5=180.00000000
D6=180.00000000
D7=0.00000000
D8=119.53725710
D9=-119.53725710







 







 






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

 





 Calc /ropt  Calc /rs     Expt [1]

 




 A
     9226.
   9205.
 9156.7503(50)

 B
     3621.
   3622.
 3609.9582(16)

 C
     2644.
   2642
 2632.4462(16)









 








 








[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