C5H7CN















 








Nitrogen

Nuclear Quadrupole Coupling Constants


in 4-Cyanocyclopentene


 








 








 








The microwave spectra of equatorial and axial conformers of 4-cyanocyclopentene were observed and assigned by Choe and Harmony [1].  Rotational constants, dipole moments, and the energy difference between conformers were reported.











equatorial, Cs
axial, Cs































At MP2/6-311+G(d,p) opt level of theory, Eeq < Eax by 2.2 kJ/mol (or 523 kcal/mol, compared with 400(60) kcal/mol reported by Choe and Harmony).











 








Calculation was made here of the 14N nqcc tensor for each conformer on MP2/6-311+G(d,p) optimized molecular structures with correction for approximate equilibrium C-CN bond lengths.  These calculated nqcc's are shown below in Tables 1 and 2.  Rotational constants and dipole moments are given in Table 3.  Structure parameters are given here in Z-matrix format.

In Tables 1 and 2, subscripts a,b,c refer to the principal axes of the inertia tensor, subscripts x,y,z to the principal axes of the nqcc tensor.  The nqcc y-axis is chosen coincident with the inertia b-axis, these are perpendicular to the Cs plane of the molecule.  ETA = (Xxx - Xyy)/Xzz.  Ø (degrees) is the angle between its subscripted parameters.

RSD is the residual standard deviation of calibration of the B3PW91/6-311+G(df,pd) model for calculation of the efg's/nqcc's.

 








 








   






Table 1.  Nitrogen nqcc's in equatorial 4-cyanocyclopentene (MHz).  Calculation was made on MP2/6-311+G(d,p) optimized structure with approximate equilibrium C-CN bond lengths.
   









Calc.
Expt.
   






14N Xaa -
 3.657




Xbb
2.103




Xcc
1.554




|Xac|
1.762



 







RSD
0.030 (1.3 %)



 







Xxx
2.093




Xyy
2.103




Xzz -
 4.197




ETA
0.00230




Øz,a
17.03




Øa,CN
17.03




Øz,CN
  0.00



 






   








 








   






Table 2.  Nitrogen nqcc's in axial 4-cyanocyclopentene (MHz).  Calculation was made on MP2/6-311+G(d,p) optimized structure with approximate equilibrium C-CN bond lengths.
   









Calc.
Expt.
   






14N Xaa -
 2.261




Xbb
2.080




Xcc
0.182




|Xac|
2.894



 







RSD
0.030 (1.3 %)



 







Xxx
2.101




Xyy
2.080




Xzz -
 4.181




ETA -
 0.00513




Øz,a
33.56




Øa,CN
33.46




Øz,CN
  0.10



 























Table 3.  4-Cyanocyclopentene.  Rotational constants (MHz) and Dipole Moments * (D)

 





      _______equatorial_______        ________axial_________


Calc
Expt [1]
 Calc
Expt [1]







 A
 6839.7
6762.66 4971.0
5095.77

 B
 1915.4
 1916.722228.8
2185.81

 C
 1588.0
 1590.60 1995.5
 1936.50







|µa|
   4.10
   3.85
   3.70
   3.48

|µc|   0.87
   1.10
   2.14
   2.51







*  B3PW91/6-311+G(df,pd) calculation on MP2/6-311+G(d,p) optimized structures with approximate equilibrium C-CN bond lengths.








 








 








[1] J.-I.Choe and M.D.Harmony, J.Mol.Spectrosc. 89,333(1981).

 








 








Table of Contents




Molecules/Nitrogen




 








 













4CNcycpentene.html






Last Modified 14 Jan 2014