CH3N[C(=O)CH3]2















 









Nitrogen


Nuclear Quadrupole Coupling Constants

in N-Methyldiacetamide

 








C1 Symmetry


Cs Symmetry




































At the MP2/6-311++G(d,p) level of theory, C1 is more stable than Cs by 1.7 kJ/mol.











Calculation of the nitrogen nqcc tensors in both C1 and Cs N-methyldiacetamide was made here on ropt molecular structures given by MP2/6-311++G(d,p) optimization.  These are compared with the experimental nqcc's [1] 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 the principal axes of the inertia tensor; x,y,z to the principal axes of the nqcc tensor.  ETA = (Xxx - Xyy)/Xzz. 


RMS is the root mean square difference between calculated and experimental diagonal nqcc's (percentage of the average magnitude of the experimental nqcc's).  RSD is the calibration residual standard deviation of the (1) B3PW91/6-311+G(df,pd) and (2) B3PW91/6-311+G(d,p) models for calculation of nitrogen efg's/nqcc's.

 








 








 








Table 1.  14N nqcc's in C1 N-Methyldiacetamide (MHz).  (1) B3PW91/6-311+G(df,pd) and (2) B3PW91/6-311+G(d,p) calculations on MP2/6-311++G(d,p) optimized structure.
 










Calc (1)
Calc (2)
  Expt. [1]
 








Xaa
1.645
1.734
1.7360(7)

Xbb
1.960
2.019
2.0388(7) *

Xcc -
 3.605
 -
 3.753
 -
 3.7748(7) *

Xab
0.038
0.030



Xac
0.116
0.121



Xbc -
 0.147
 -
 0.155












RMS
0.120 (4.8 %)
0.017 (0.67 %)
 

RSD
0.030 (1.3 %)
0.086 (3.8 %)












Xxx
1.643
1.734



Xyy
1.968
2.026



Xzz -
 3.612
 - 3.760



ETA
0.0899
0.0774













 








* Derived here from Xaa and Xbb - Xcc  = 5.8136(12) MHz.

 








 








 








Table 2.  14N nqcc's in Cs N-Methyldiacetamide (MHz).  (1) B3PW91/6-311+G(df,pd) and (2) B3PW91/6-311+G(d,p) calculations on MP2/6-311++G(d,p) optimized structure.
 










Calc (1)
Calc (2)
  Expt. [1]
 








Xaa
1.664
1.756
1.7360(7)

Xbb
1.920
1.977
2.0388(7) *

Xcc -
 3.584
 -
 3.733
 -
 3.7748(7) *

Xab
0.062
0.056












RMS
0.136 (5.4 %)
0.044 (1.8 %)
 

RSD
0.030 (1.3 %)
0.086 (3.8 %)












Xxx
1.650
1.742



Xyy
1.934
1.991



Xzz -
 3.584
 - 3.733



ETA
0.0792
0.0665













 








 








OBSERVATION:  The B3PW91/6-311+G(d,p) model performs much better here than does the B3PW91/6-311+G(df,pd) model.  This is consistently the case for pi-electron conjugated amides.



















Table 3.  N-Methyldiacetamide.  MP2/6-311++G(d,p) Structure parameters (Å and degrees).










 N
 C,1,B1
 C,1,B2,2,A1
 O,2,B3,1,A2,3,D1,0
 O,3,B4,1,A3,2,D2,0
 C,1,B5,2,A4,4,D3,0
 H,6,B6,1,A5,2,D4,0
 H,6,B7,1,A6,2,D5,0
 H,6,B8,1,A7,2,D6,0
 C,2,B9,1,A8,3,D7,0
 H,10,B10,2,A9,1,D8,0
 H,10,B11,2,A10,1,D9,0
 H,10,B12,2,A11,1,D10,0
 C,3,B13,1,A12,2,D11,0
 H,14,B14,3,A13,1,D12,0
 H,14,B15,3,A14,1,D13,0
 H,14,B16,3,A15,1,D14,0
























 Cs Symmetry
  C1 Symmetry









 B1=1.40687544
 B2=1.42573562
 B3=1.21954088
 B4=1.21960555
 B5=1.46868542
 B6=1.08737397
 B7=1.09179243
 B8=1.09179243
 B9=1.51712959
 B10=1.09299745
 B11=1.09299745
 B12=1.08921446
 B13=1.50791574
 B14=1.09046133
 B15=1.09046133
 B16=1.09010462
 A1=124.44064877
 A2=123.54350539
 A3=119.30844501
 A4=119.42902783
 A5=107.35726617
 A6=110.86209419
 A7=110.86209419
 A8=115.38636853
 A9=111.36139992
 A10=111.36139992
 A11=107.2453843
 A12=119.34321107
 A13=111.16054199
 A14=111.16054199
 A15=106.47052939
 D1=0.
 D2=180.
 D3=180.
 D4=180.
 D5=-61.01131384
 D6=61.01131384
 D7=180.
 D8=-60.2595961
 D9=60.2595961
 D10=180.
 D11=0.
 D12=-59.39154945
 D13=59.39154945
 D14=180.
  B1=1.40556954
 B2=1.42259903
 B3=1.21984811
 B4=1.21962035
 B5=1.46813493
 B6=1.08795677
 B7=1.09442349
 B8=1.08828618
 B9=1.51675788
 B10=1.09370186
 B11=1.09298438
 B12=1.08931537
 B13=1.50807695
 B14=1.09010761
 B15=1.09102183
 B16=1.09058816
 A1=123.41544403
 A2=123.01739987
 A3=118.9317703
 A4=120.18292313
 A5=107.98699172
 A6=111.47741872
 A7=109.98076803
 A8=115.83604469
 A9=111.09627686
 A10=111.60076893
 A11=107.18320127
 A12=119.0939365
 A13=111.89739169
 A14=110.31124851
 A15=106.62570919
 D1=0.79735294
 D2=161.46684202
 D3=167.56159794
 D4=164.26734956
 D5=-76.89490376
 D6=45.09373615
 D7=-179.43713048
 D8=-62.07456254
 D9=58.67625999
 D10=178.50903261
 D11=-21.41387913
 D12=-41.54575375
 D13=77.520002
 D14=-163.07074755










 














Table 4.  N-Methyldiacetamide.  MP2/6-311++G(d,p) Rotational Constants (MHz).








    Cs     C1     Expt [1]







A
   3146.
   3136.
 3155.4500(37)

B
   1789.
   1790.
 1791.2822(20)

C
   1165.
   1179.
 1170.92822(40)









 








 








[1] R.Kannengießer, K.Eibl, H.V.L.Nguyen, and W.Stahl,  Abstract TG12, 70th International Symposium on Molecular Spectroscopy, Champaign-Urbana, 2015.

 








 








Acetamide N-Methylacetamide N,N-Dimethylacetamide

Formimide
 N,N-Diethylacetamide Uracil
Thymine

2-Pyridone







 








 








Table of Contents




Molecules/Nitrogen




 








 













NMeDiacetamide.html






Last Modified 17 July 2015