H(O=)C-N(-H)CH3















 









Nitrogen


Nuclear Quadrupole Coupling Constants


in N-Methylformamide


 








 








Nitrogen nqcc's in trans and cis N-methylformamide were determined by Kawashima et al. [1].

 










trans



cis




























 









At MP2/aug-cc-pVTZ level of theory, Etrans < Ecis by 6.0 kJ/mol


 



















Calculation of the N nqcc tensor in both trans and cis N-methylformamide was made here on Cs  (assumed) molecular structures given by MP2/aug-cc-pVTZ and HF/6-311++G(3df,3pd)  optimization.  Calculated and experimental [1] nqcc's are compared in Tables 1 and 2.  Structure parameters are given in Table 3, rotational constants in Table 4.

 








In Tables 1 and 2, subscripts a,b,c refer to principal axes of the inertia tensor, subscripts x,y,z to principal axes of the nqcc tensor.  ETA = (Xxx - Xyy)/Xzz.

RMS is the root measn square difference between calculated and experimental diagonal nqcc's (percent of the average of the absolute experimental nqcc's).  RSD is the residual standard deviation of the calibration of the computional model for calculation of the nqcc's.

 








 








 








Table 1.  14N nqcc's in trans N-Methylformamide, A (MHz).  Calculation was made on  MP2/aug-cc-pVTZ and HF/6-311++G(3df,3pd) optimized structures.
 










Calc /MP2

Calc /HF

 Expt [1]
 








Xaa
1.902
1.897
1.8971(54)

Xbb
2.159
2.156
2.13865 *

Xcc - 4.060 - 4.053 - 4.03575 *

|Xab|
0.161
0.246




 







RMS
0.019 (0.69 %)
0.014 (0.52 %)



RSD
0.030 (1.3 %)
0.030 (1.3 %)



 







Xxx
1.824
1.749



Xyy
2.237
2.304



Xzz - 4.060 - 4.053



ETA
0.102
0.137



 








 








* Derived here from Xaa and Xbb - Xcc  =  6.1744(12) MHz.

 









 









 








Table 2.  14N nqcc's in cis N-Methylformamide, E (MHz).  Calculation was made on  MP2/aug-cc-pVTZ and HF/6-311++G(3df,3pd) optimized structures.
 










Calc /MP2

Calc /HF

 Expt [1]
 








Xaa
2.334
2.338
2.3508(29)

Xbb
1.911
1.892
1.9182 *


Xcc - 4.245 - 4.230 - 4.2690 *


|Xab|
0.284
0.309




 







RMS
0.017 (0.61 %)
0.028 (0.97 %)



RSD
0.030 (1.3 %)
0.030 (1.3 %)



 







Xxx
1.769
1.733



Xyy
2.476
2.497



Xzz - 4.245 - 4.230



ETA
0.167
0.180



 








 









* Derived here from Xaa and Xbb - Xcc  =  6.1872(84) MHz.

 









 








 





Table 3.  N-Methylformamide.  MP2/aug-cc-pVTZ and HF/6-311++G(3df,3pd) selected structure parameters (Å and degrees).  Complete structures are given here in Z-matrix format.
 





trans   MP2   HF





C(3)O 1.2213 1.1893
C(3)N 1.3574 1.3429
NC(6) 1.4484 1.4451
NH(2) 1.0055 0.9903
OC(3)N 125.24 125.83
C(6)NC(3) 122.66 123.81
C(3)NH(2) 117.46 117.28
OC(3)NC(6)     0. (sym)     0. (sym)


OC(3)NH(2) 180. (sym) 180. (sym)












cis
  MP2
  HF






C(3)O 1.2209
1.1888
C(3)N 1.3550
1.3425
NC(6) 1.4512
1.4447
NH(2) 1.0072
0.9923
OC(3)N 125.13
125.15
C(3)NH(2) 116.35
116.35
OC(3)NC(6) -180. (sym)
-180. (sym)
OC(3)NH(2)      0. (sym)
     0. (sym)
 







 








 













Table 3.   N-Methylformamide.  Rotational Constants (MHz).  
 




trans Calc /MP2 Calc /HF   Expt. [1]






A 19862.2 20726.8 19986.8962(30)

B   6154.7   6168.1   6405.2571(15)

C   4841.8   4897.5   4902.4309(15)






cis
Calc /MP2
Calc /HF







A
44274.7
45346.4


B
  4384.5
  4478.8


C
  4091.8
  4181.6



 








 








[1]  Y.Kawashima, T.Usami, R.D.Suenram, G.Yu.Golubiatnikov, and E.Hirota, J.Mol.Spectrosc. 263,11(2010).

 









A.C.Fantoni and W.Caminati, J.Chem.Soc. Farad.Trans. 92,343(1996).


 









 








Formamide Acetamide N-Methylacetamide N-Ethylformamide

 








 








Table of Contents




Molecules/Nitrogen




 








 













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Last Modified 24 May 2015