(CH3)3C-N(H)C(=O)H















 









Nitrogen


Nuclear Quadrupole Coupling Constants

in N-tert-Butylformamide

 


















The low resolution microwave spectrum of each of the following conformers of N-tert-butylformamide was first observed and assigned by N.S.True [1], and subsequently revisited at higher resolution by Kannengießer [2].











syn OCNC = 0o

anti OCNC = 180o






At B3LYP/cc-pVTZ

level of theory,

Esyn < Eanti by  

7.3 kJ/mole














Calculation of the nitrogen nqcc tensor in each conformer was made here on ropt molecular structure given by HF/6-311++G(3df,3pd) and MP2/6-311++G(d,p) optimization (assuming Cs symmetry).  These calculated nqcc's are compared with the experimental values [2] in Tables 1 and 2.  Structure parameters are given in Table 3, rotational constants and dipole moments 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. 


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

 








 








 








Table 1.  14N nqcc's in syn N-tert-Butylformamide (MHz).  Calculation was made on (1) HF/6-311++G(3df,3pd) and (2) MP2/6-311++G(d,p) optimized structures.
 










Calc (1)
Calc (2)
  Expt [2]
 








Xaa
1.790
1.799
1.80315(71)

Xbb - Xcc
5.862
5.956
5.7563(17)

Xbb
2.036
2.078
1.9766(18) *

Xcc -
 3.826
 -
 3.878
 -
 3.7797(18) *

|Xab|
0.205
0.093












RMS
0.044 (1.8 %)
0.082 (3.2 %)



RSD
0.030 (1.3 %)
0.030 (1.3 %)












Xxx
1.674
1.771



Xyy
2.152
2.106



Xzz -
 3.826
 - 3.878



ETA
0.125
0.086













 








* Derived here from experimental Xaa and Xbb - Xcc

 








 








 








Table 2.  14N nqcc's in anti N-tert-Butylformamide (MHz).  Calculation was made on (1) HF/6-311++G(3df,3pd) and (2) MP2/6-311++G(d,p) optimized structures.
 










Calc (1)
Calc (2)
  Expt [2]
 








Xaa
2.125
2.121
2.1345(38)

Xbb - Xcc
5.939
6.064
5.710(11)

Xbb
1.907
1.971
1.788(12) *

Xcc -
 4.032
 -
 4.092
 -
 3.922(12) *

|Xab|
0.255
0.203












RMS
0.094 (3.6 %)
0.144 (5.5 %)



RSD
0.030 (1.3 %)
0.030 (1.3 %)












Xxx
1.738
1.830



Xyy
2.294
2.262



Xzz -
 4.032
 - 4.092



ETA
0.138
0.106













 








* Derived here from experimental Xaa and Xbb - Xcc

 








 






Table 3.  N-tert-Butylformamide.  Selected structure parameters,  ropt (Å and degrees).  Optimized structures (1) HF/6-311++G(3df,3pd) and (2) MP2/6-311++G(d,p).  Complete structures are given here is Z-matrix format.










    syn ropt (1)ropt (2)





C(6)N 1.4709
 1.4716

NC(3) 1.3419
 1.3627

C(3)O 1.1906
 1.2224

C(6)NC(3) 126.93
 125.66

NC(3)O 126.62
 125.89

OC(3)NC(6)     0.
     0.






















    anti ropt (1)ropt (2)





C(6)N 1.4659
 1.4698

NC(3) 1.3421
 1.3621

C(3)O 1.1911
 1.2228

C(6)NC(3) 126.76
 126.00

NC(3)O 124.67
 124.67

OC(3)NC(6) 180.
 180.














 








 




Table 4.  N-tert-Butylformamide (MHz).  Rotational constants (MHz).  Calculation was made on (1) HF/6-311++G(3df,3pd) and (2) MP2/6-311++G(d,p) optimized structures.








Calc (1)
 Calc (2)       Expt [2]






syn
 A
   4117
   4095
 4079.105661(91)

B
   1924
   1924
 1927.547557(43)

C
   1842
   1840
 1843.423060(41)






anti A
   4371
   4356
 4331.7(26)

B
   1598
   1577
 1579.85415(40)

C
   1575
   1554
 1558.72921(44)



 








 








[1] N.S.True, J.Mol.Struct. 112,333(1984).

[2] Raphaela Kannengießer, "Structures and Dynamics of Formamides, Acetamides, and Propionamides" Dissertation, RWTH Aachen University, Institute of Physical Chemistry, 2017.

 








 








Formamide N-Methylformamide N-Ethylformamide

Cyanoformamide
 N-Vinylformamide
 N,N-Dimethylformamide

Methyl ethyl formamide
 cis-Formanilide
 trans-Formanilide


 








 








Table of Contents




Molecules/Nitrogen




 








 













NtBF.html






Last Modified 14 Jan 2018