Quinoxaline




 




 

Nitrogen


Nuclear Quadrupole Coupling Constants


in Quinoxaline


 







 
Nitrogen nqcc tensors in quinoxaline were calculated on a molecular structure optimized at the B3P86/6-31G(3d,3p) level of theory (ropt).  These calculated nqcc's are compared with the experimental values of McNaughton et al. [1] in Table 1.  Structure parameters are given in Table 2, rotational constants and electric dipole moments in Table 3.
 
In Table 1, subscripts a,b,c refer to principal axes of the inertia tensor, subscripts x,y,z to 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.  Ø (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 stand deviation of calibration of the B3PW91/6-311+G(df,pd) model for calculation of the nqcc's.
 
 
   







Table 1. Nitrogen nqcc's in Quinoxaline (MHz).  Calculation was made on the B3P86/6-31G(3d,3p) ropt structure.
   










Calc.
Expt. [1]
   






14N(1,2) Xaa 1.203 1.2123(61)
Xbb - 4.973 - 4.9402 *
Xcc 3.770 3.7279 *
Xab ± 0.272
 
RMS 0.032 (0.96 %)
RSD 0.030 (1.3 %)
 
Xxx 1.215
Xyy 3.770
Xzz - 4.985
ETA 0.512
Øz,b 2.51
Øb,bi 0.75
Øz,bi** 3.27
 
 
* Calculated here from experimental Xaa and Xbb - Xcc = -8.6681(64) MHz.
** The z-axis makes an angle of 3.27 with the external bisector ('bi') of the CNC angle and tilts toward C(3,4).  See Table 2 for atomic numbering.
 
Table 2. Quinoxaline and Pyrazine.  Selected molecular structure parameters, B3P86/6-31G(3d,3p) ropt (Å and degrees).  The complete structure of quinoxaline is given here in Z-matrix format.
 
Quinoxaline Pyrazine
C(4)N 1.3592 1.3317
NC(11) 1.3099 1.3317
C(4)NC(11) 116.14 115.77
 
 
 
Table 3.  Quinoxaline, ropt.  Rotational constants (MHz) and B3PW91/6-311+G(df,pd) calculated dipole moments (D).
 
 Calc.     Expt. [1]
A 3187.98 3165.90728(64)
B 1319.30 1310.636904(72)
C   933.14   927.130503(46)
µa   0.56
 
 
[1] D.McNaughton, P.D.Godfrey, M.K.Jahn, D.A.Dewald, and J.-U.Grabow, J.Chem.Phys. 134,154305(2011).

 








 







Pyrazine Quinazoline Phthalazine 1,10-Phenanthroline
Acridine Quinoline Isoquinoline Phenanthridine
 

 








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Molecules/Nitrogen
 

 













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Last Modified 20 April 2011