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Pyrimidine
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Nitrogen
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Nuclear
Quadrupole Coupling Constants |
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in Pyrimidine |
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Nitrogen nqcc's in pyrimidine were calculated on the B3P86/6-31G(3d,3p)
optimized molecular structure, and on the heavy atom substitution structure
of Kisiel et al. [1] with the CH parameters of the optimized structure.
These are compared with the experimental coupling constants [1] in Tables
1 and 2. The structure parameters are compared in Table 3.
In Table 4, atomic coordinates are given for the ropt structure. |
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In Tables 1 and 2, subscripts a,b,c refer to the principal axes of the inertia
tensor, subscripts x,y,z to the principal axes of the nqcc tensor.
The nqcc y-axis is chosen coincident with the inertia c-axis, these
are perpendicular to the plane of the molecule. Ø (degrees)
is the angle between its subscripted parameters. ETA = (Xxx
- Xyy)/Xzz. |
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RMS is the root mean square
difference between calculated and experimental nqcc's (percentage of
average experimental nqcc). RSD is the residual standard deviation
of calibration of the B3PW91/6-311+G(df,pd) model for calculation of
the nqcc's. |
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Table 1. Nitrogen
nqcc's in Pyrimidine (MHz). Calculation was made
on the B3P86/6-31G(3d,3p) ropt structure. |
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Calc. |
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Expt. [1] |
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14N(1,3) |
Xaa |
- |
3.106 |
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3.1004(7) |
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Xbb |
- |
0.258 |
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0.2554(7) |
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Xcc |
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3.364 |
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3.3558(7) |
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Xab |
± |
2.718 |
± |
2.76(7) |
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RMS |
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0.006 (0.3 %) |
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RSD |
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0.030 (1.3 %) |
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Xxx |
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1.386 |
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1.43(6) |
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Xyy |
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3.364 |
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3.3558(7) |
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Xzz |
- |
4.750 |
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4.78(6) |
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ETA |
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0.416 |
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Øz,a |
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31.17 |
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31.4(3) |
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Øa,bi |
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31.54 |
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Øz,bi* |
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0.36 |
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* The z-axis makes an angle of 0.36o with the
external bisector ( 'bi' ) of the CNC angle and tilts toward C(2).
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Table 2. Nitrogen
nqcc's in Pyrimidine (MHz). Calculation was made
on the heavy atom rs structure [1] with the CH parameters of the
optimized structure. |
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Calc. |
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Expt. [1] |
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14N(1,3) |
Xaa |
- |
3.070 |
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3.1004(7) |
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Xbb |
- |
0.286 |
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0.2554(7) |
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Xcc |
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3.357 |
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3.3558(7) |
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Xab |
± |
2.739 |
± |
2.76(7) |
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RMS |
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0.025 (1.1 %) |
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RSD |
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0.030 (1.3 %) |
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Xxx |
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1.394 |
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1.43(6) |
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Xyy |
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3.357 |
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3.3558(7) |
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Xzz |
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4.751 |
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4.78(6) |
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ETA |
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0.413 |
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Øz,a |
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31.53 |
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31.4(3) |
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Øa,bi |
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31.5(2) |
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31.5(2) |
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Øz,bi* |
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0 |
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0 |
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* The z-axis is coincident with the external
bisector ('bi') of the CNC angle. |
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| Table 3. Molecular structure parameters, B3P86/6-31G(3d,3p) ropt and heavy atom rs [1] (Å and degrees). |
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ropt |
rs [1] |
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C(2)N(3) |
1.3320 |
1.337(2) |
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N(3)C(4) |
1.3328 |
1.332(3) |
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C(4)C(5) |
1.3877 |
1.393(2) |
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C(2)H(2) |
1.0876 |
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C(4)H(4) |
1.0879 |
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C(5)H(5) |
1.0835 |
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N(1)C(2)N(3) |
127.38 |
127.2(3) |
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C(2)N(3)C(4) |
115.70 |
115.8(3) |
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N(3)C(4)C(5) |
122.40 |
122.4(3) |
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C(4)C(5)C(6) |
116.44 |
116.4(2) |
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C(5)C(4)H(4) |
121.16 |
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| Table 4. Atomic coordinates,
B3P86/6-31G(3d,3p) ropt |
| (More figures are shown
than are significant.) |
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a (Å) |
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b (Å) |
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N(1,3) |
± |
1.193960 |
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0.685056 |
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C(2) |
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0.0 |
- |
1.275471 |
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C(4,6) |
± |
1.179635 |
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0.647712 |
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C(5) |
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0.0 |
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1.378622 |
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H(2) |
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0.0 |
- |
2.363039 |
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H(4,6) |
± |
2.148487 |
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1.142540 |
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H(5) |
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0.0 |
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2.462154 |
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[1] Z.Kisiel, L.Pszczólkowski, J.C.López, J.L.Alonso,
A.Maris, and W.Caminati, J.Mol.Spectrosc. 195,332(1999).
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Pyridine |
Pyrazine |
1,3,5-Triazine |
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2-Fluoropyrimidine |
2-Chloropyrimidine |
2-Bromopyrimidine |
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Table of Contents |
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Molecules/Nitrogen |
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Pyrimidine.html |
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Last
Modified 24 May 2003 |
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