(CH2CH3)2N-C(=O)CH2CH3















 









Nitrogen


Nuclear Quadrupole Coupling Constants

in N,N-Diethylpropionamide

 


















The microwave spectrum of each of the following conformers of N,N-diethylpropionamide was observed and assigned by Kannengiesser et al. [1].





















Conformer OPM

Conformer OMM






EOPM  <  EOMM


























Calculation of the nitrogen nqcc tensor in each conformer was made in Ref. [1] on an ropt molecular structure given by MP2/6-311++G(d,p), and here on an ropt molecular structure given by HF/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.  Ø (degrees) is the angle between its subscripted parameters.

RMS is the root mean square difference between calculated and experimental diagonal 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 efg's/nqcc's.

 








 








 








Table 1.  14N nqcc's in N,N-Diethylpropionamide, conformer OPM (MHz).  Calculation was made on MP2/6-311++G(d,p) and HF/6-311++G(d,p) optimized structures.
 










Calc /MP2 [1]
Calc /HF
  Expt. [1]
 








Xaa
1.949
1.962
1.97018(79)

Xbb - Xcc
4.243
4.396
4.2749(14)

Xbb
1.147
1.217
1.1524(8) *

Xcc -
 3.096
 -
 3.179
 -
 3.1225(8) *

Xab -
 0.244
 -
 0.165



Xac
0.544
0.523



Xbc
2.662
2.679












RMS
0.020 (0.95 %)
0.050 (2.4 %)
 

RSD
0.030 (1.3 %)
0.030 (1.3 %)












Xxx
2.004
1.997
2.025(8) **

Xyy
2.430
2.495
2.430(31) **

Xzz -
 4.434
 - 4.492 -
 4.455(31) **

ETA
0.0962
0.111
0.0909(72) **

Øz,n***

















 








* Calculated here from experimental Xaa and Xbb - Xcc

** Calculated here - using Kisiel's QDIAG.f program - from experimental Xaa and Xbb - Xcc and MP2 off-diagonal elements.  For these latter, we assign an estimated uncertainity of 2 x RMS, that is 0.040 MHz.

*** Angle between normal to C(2)C(5)C(7) plane (see below) and z-principal axis of the nqcc tensor.

 








 








 








Table 2.  14N nqcc's in N,N-Diethylpropionamide, conformer OMM (MHz).  Calculation was made on MP2/6-311++G(d,p) and HF/6-311++G(d,p) optimized structures.
 










Calc /MP2 [1]
Calc /HF
  Expt. [1]
 








Xaa
1.818
1.787
1.79861(93)

Xbb - Xcc
6.610
6.701
6.6695(15)

Xbb
2.396
2.457
2.4354(9) *

Xcc -
 4.214
 -
 4.244
 -
 4.2340(9) *

Xab -
 0.057
 -
 0.187



Xac -
 1.062
 -
 1.732



Xbc -
 0.336
 -
 0.319












RMS
0.028 (0.98 %)
0.015 (0.55 %)
 

RSD
0.030 (1.3 %)
0.030 (1.3 %)












Xxx
2.000
1.982
1.980(18)  **

Xyy
2.413
2.483
2.452(6) **

Xzz -
 4.413
 -
 4.465
 -
 4.432(19) **

ETA
0.0937
0.112
0.106(4) **

Øz,n***

















 








* Calculated here from experimental Xaa and Xbb - Xcc

** Calculated here - using Kisiel's QDIAG.f program - from experimental Xaa and Xbb - Xcc and MP2 off-diagonal elements.  For these latter, we assign an estimated uncertainity of 2 x RMS, that is 0.056 MHz.

*** Angle between normal to C(2)C(5)C(7) plane (see below) and z-principal axis of the nqcc tensor.

 








 






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











Conformer OPM






ropt /MP2 ropt /HF





C(2)N 1.4576 1.4553

C(3)N 1.4614 1.4604

C(4)N 1.3709 1.3584

C(2)NC(3) 117.32 117.06

C(3)NC(4) 117.85 118.10

C(4)NC(2) 124.73 124.83























Conformer OMM






ropt /MP2 ropt /HF





C(2)N 1.4638
 1.4630

C(3)N 1.4571
 1.4556

C(4)N 1.3716
 1.3593

C(2)NC(3) 118.01
 117.82

C(3)NC(4) 124.77
 124.62

C(4)NC(2) 117.19
 117.44





Note:  The extent to which the three CNC angles sum to 360o is the extent to which the N atom is co-planar with C(2)C(3)C(4).










 














Table 4.  N,N-Diethypropionamide.  Rotational Constants (MHz).  Calculation was made on the  MP2/6-311++G(d,p) and HF/6-311++G(d,p) optimized structures.








Calc /MP2 [1]
 Calc /HF
     Expt [1]






OPM
 A
   1915.4
   1931.2
 1924.21584(15)

B
   1220.8
   1215.1
 1214.565984(56)

C
     833.7
     831.7
   832.070891(42)






OMM A
   2071.2
   2073.5
 2070.06910(24)

B
   1177.1
   1175.8
 1180.371868(71)

C
     856.3
     851.4
   857.533403(51)



 








 








[1]  R.Kannengiesser, W.Stahl, and H.V.L.Nguyen, J.Phys.Chem. A 120,5979(2016).

 








 








Acetamide N-Methylacetamide N,N-Dimethylacetamide

 








 








Table of Contents




Molecules/Nitrogen




 








 













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Last Modified 17 Sept 2016