C4H6N2
































 























Nitrogen


Nuclear Quadrupole Coupling Constants

in 5-Methylimidazole

 








 
 N-Methylimidazole 2-Methylimidazole 4-Methylimidazole






















14N nuclear quadrupole coupling constants in 5-methylimidazole were determined by Gougoula, et al. [1].











Calculation of the 14N nuclear quadrupole coupling constants was made here on B3LYP/cc-pVTZ  opimized molecular structure.

 








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 5-Methylimidazole (MHz).  Calculation was made on the ropt = B3LYP/cc-pVTZ optimized structure.
 
 








Calc /ropt
Expt [1]
 
 





14N(1) Xaa
1.132
1.1630(66)


Xbb - Xcc
4.212
4.167(10)


Xbb
1.540
1.5020 *


Xcc -
 2.672
 -
 2.6650 *


Xab
0.070












RMS
0.031 (1.8 %)




RSD
0.030 (1.3 %)




 






Xxx
1.121




Xyy
1.551




Xzz -
 2.672




ETA
0.161




Øz,c
 zero




 






 








* Calculated here from experimental Xaa and Xbb - Xcc

 








 








 
 





Table 2.  Pyridinic 14N(3) nqcc's in 5-Methylimidazole (MHz).  Calculation was made on the ropt = B3LYP/cc-pVTZ optimized structure.
 
 








Calc /ropt
Expt [1]
 
 





14N(3) Xaa -
 2.113
 -
 2.0975(57)


Xbb - Xcc -
 2.427
 -
 2.415(12)


Xbb -
 0.157
 -
 0.1588 *


Xcc
2.270
2.2563 *


Xab -
 2.802












RMS
0.012 (0.8 %)




RSD
0.030 (1.3 %)




 






Xxx
1.832




Xyy
2.270




Xzz -
 4.103




ETA
0.107




Øz,bi**






 






 








* Calculated here from experimental Xaa and Xbb - Xcc

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

 








 


Table 3.  5-Methylimidazole:  Structure parameters,  ropt = B3LYP/cc-pVTZ (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,4,B7,3,A6,2,D5,0
 C,5,B8,4,A7,3,D6,0
 H,9,B9,5,A8,4,D7,0
 H,9,B10,5,A9,4,D8,0
 H,9,B11,5,A10,4,D9,0


      ropt(1)




 B1=1.36534095
 B2=1.30761831
 B3=1.37618608
 B4=1.36930405
 B5=1.00513611
 B6=1.0775453
 B7=1.07739642
 B8=1.48881962
 B9=1.08857341
 B10=1.09312304
 B11=1.09312304
 A1=111.48446853
 A2=105.29186625
 A3=111.2182111
 A4=126.30768476
 A5=122.39597562
 A6=121.46816418
 A7=132.4558494
 A8=109.70279315
 A9=112.0627183
 A10=112.0627183
 D1=0.
 D2=0.
 D3=180.
 D4=180.
 D5=180.
 D6=180.
 D7=0.
 D8=119.4596224
 D9=-119.4596224







 







 





Table 4.  5-Methylimidazole: Rotational Constants (MHz).

 




  Calc /ropt     Expt [1]

 



 A
     9128.
 9054.9327(15)

 B
     3483.
 3471.74371(51)

 C
     2561.
 2549.30663(32)








 








 








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

 








 








Table of Contents




Molecules/Nitrogen




 








 













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Last Modified 9 Oct 2019