Pyrrolidine

PDF  equatorial

C4H8NH PDF  axial
 
 
 


Nitrogen


Nuclear Quadrupole Coupling Constants

in Pyrrolidine (eq and ax)


 







 

 


 




Calculation of the nitrogen nqcc's in equatorial and axial pyrrolidine (aka tetrahydropyrrole) was made here on the ro molecular structures of Velino et al. [1], and on molecular structures given by MP2/6-311+G(2d,2p) optimization, ropt.  These are compared with the experimental nqcc's [2,3] in Tables 1 and 2.  Structure parameters are given in Table 3, ropt rotational constants 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.  The nqcc y-axis is chosen coincident with the inertia b-axis, these are perpendicular to the molecular symmetry plane.  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 the average of the magnitudes of the experimental nqcc's).  RSD is the calibration residual standard deviation of the B3PW91/6-311+G(df,pd) model for calculation of nitrogen nqcc's.
 
 
   







Table 1. 14N nqcc's in equatorial Pyrrolidine (MHz).  Calculation was made on the ro and ropt molecular structures.
   








Calc. / ro 
Calc. / ropt 
Expt. [2]
   






Xaa 2.160 2.127 2.12(5)
Xbb 2.832 2.826 2.84 *
Xcc - 4.992 - 4.953 - 4.96 *
|Xac| 0.629 0.673
 
RMS 0.03 (0.90 %) 0.01 (0.31 %)  
RSD 0.030 (1.3 %) 0.030 (1.3 %)
 
Xxx 2.215 2.191
Xyy 2.832 2.826
Xzz - 5.047 - 5.016
ETA 0.122 0.127
Øz,a   95.0   95.4
Øa,NH   16.6   16.6
Øz,NH 111.6 112.0
 
 
* Calculated here from Xaa and Xbb - Xcc = 7.80(8) MHz [1].
 
 
   







Table 2. 14N nqcc's in axial Pyrrolidine (MHz).  Calculation was made on the ro and ropt molecular structures.
   








Calc. / ro 
Calc. / ropt 
Expt. [3]
   






Xaa - 3.502 - 3.607 - 3.0(1)
Xbb 2.825 2.746 3.1(1)
Xcc 0.677 0.861
|Xac| 2.886 2.724
 
RSD 0.030 (1.3 %) 0.030 (1.3 %)
 
Xxx 2.151 2.149
Xyy 2.825 2.746
Xzz - 4.976 - 4.896
ETA 0.136 0.122
Øz,a   27.0   25.3
Øa,NH   84.9   86.6
Øz,NH 111.9 111.9
 
 
 
 
 
Table 3. Heavy atom and NH molecular structure parameters, ro and MP2/6-311+G(2d,2p) ropt (Å and degrees).
Complete molecular structures for the equatorial conformer are given here, and for the axial conformer, here.
 
ro [1] ropt
 
Equatorial NH 1.017 1.0111
C(1)N 1.464 1.4662
C(1)C(2) 1.547 1.5345
C(2)C(3) 1.558 1.5513
C(4) - - - C(1) 2.314 2.3045
C(2)C(3)C(4) 104.1 104.21
C(4)NC(1) 104.4 103.60
C(4)NC(1)-NH 126.9 126.94
C(2)C(1)C(4)N 133.0 132.74
 
 
Axial NH 1.006 1.0136
C(1)N 1.477 1.4698
C(1)C(2) 1.547 1.5445
C(2)C(3) 1.555 1.5494
C(4) - - - C(1) 2.309 2.3007
C(2)C(3)C(4) 104.1 104.08
C(4)NC(1) 102.9 103.01
C(4)NC(1)-NH 122.2 120.40
C(2)C(1)C(4)N 142.4 142.54


 
 
Table 4.  Pyrrolidine Rotational Constants (MHz).  MP2/6-311+G(2d,2p)  ropt structures.
 
  eq ropt eq Expt. [1] ax ropt  ax Expt. [2]
A 6918.6 6864.678(5)
6885.9
6834.536(5)
B 6843.4 6791.950(5)
6717.9
6677.844(11)
C 3939.5 3902.3(20)
3916.2
3888.063(1)
 
 
[1] B.Velino, A.Millemaggi, A.Dell' Erba, and W.Caminati, J.Mol.Struct. 599,89(2001).

[2] W.Caminati, A.Dell' Erba, G.Maccaferri, and P.G.Favero, J.Mol.Spectrosc. 191,45(1998).
[3] W.Caminati, H.Oberhammer, G.Pfafferatt, R.R.Filguerira, and C.H.Gomez, J.Mol.Spectrosc. 106,217(1984).

 








 







 N-Methyl-Pyrrole Dimethylamine Pyrrole
 

 








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Last Modified 16 March 2006