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5-CH3-C3H2NO
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Nitrogen
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Nuclear
Quadrupole Coupling Constants |
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in 5-Methyloxazole |
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Assuming Cs symmetry, the in-plane methyl hydrogen in 5-methyloxazole may be cis
or trans with respect to the ring oxygen. Calculation of the nitrogen nqcc's
was made here on cis and trans
conformer structures given by B3PW91/6-31G(2d,2pd) optimization.
These are compared with the experimental nqcc's of Fliege [1] in
Tables 1 and 2. |
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For calculation at the B3PW91/6-31G(2d,2pd) level
of theory, Etrans < Ecis by 1.1 kcal/mol.
At the B3PW91/6-311+G(df,pd) level, Etrans <
Ecis by 1.2 kcal/mol. Structure parameters and atomic coordinates
are given in Tables 3 and 4 for the lower energy trans conformer. |
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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. The nqcc y-axis is chosen
coincident with the inertia c-axis, these are perpendicular to the
molecular plane. 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 diagonal nqcc's (percentage of the average
of the magnitudes of the experimental nqcc's). RSD is the calibration
residual standard deviation for the B3PW91/6-311+G(df,pd) model for calculation
of the nqcc's. |
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Table 1. Nitrogen nqcc's in 5-Methyloxazole, trans (MHz). Calculation
was made on the B3PW91/6-31G(2d,2pd) ropt structure. |
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Calc. |
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Expt. [1] |
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14N |
Xaa |
- |
2.304 |
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2.215(13) |
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Xbb |
- |
0.158 |
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0.201(12) |
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Xcc |
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2.462 |
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2.416(12) |
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|Xab| |
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2.703 |
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2.860 |
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RMS |
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0.063 (3.9 %) |
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RSD |
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0.030 (1.3 %) |
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Xxx |
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1.677 |
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1.824 |
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Xyy |
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2.462 |
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2.416 |
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Xzz |
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4.140 |
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4.240 |
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ETA |
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0.190 |
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Øz,a |
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34.17 |
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35.3 |
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Øa,bi |
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29.87 |
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Øz,bi * |
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4.30 |
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* The z-axis makes an angle
of 4.30o with the external bisector ( 'bi' ) of the C(2)N(3)C(4)
angle, and tilts toward C(4). |
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Table 2. Nitrogen nqcc's in 5-Methyloxazole, cis (MHz). Calculation
was made on the B3PW91/6-31G(2d,2pd) ropt structure. |
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Calc. |
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Expt. [1] |
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14N |
Xaa |
- |
2.344 |
- |
2.215(13) |
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Xbb |
- |
0.148 |
- |
0.201(12) |
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Xcc |
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2.492 |
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2.416(12) |
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|Xab| |
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2.708 |
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2.860 |
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RMS |
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0.092 (5.7 %) |
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RSD |
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0.030 (1.3 %) |
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| Table 3. 5-Methyloxazole, trans. Molecular structure parameters, ropt (Å
and degrees). |
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O(1)C(2) |
1.3511 |
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C(2)N(3) |
1.2895 |
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N(3)C(4) |
1.3865 |
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C(4)C(5) |
1.3565 |
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C(5)O(1) |
1.3680 |
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C(2)H(2) |
1.0781 |
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C(4)H(4) |
1.0780 |
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C(5)O(1)C(2) |
104.58 |
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O(1)C(2)N(3) |
114.89 |
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C(2)N(3)C(4) |
103.74 |
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N(3)C(4)C(5) |
109.74 |
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C(4)C(5)O(1) |
107.05 |
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O(1)C(2)H(2) |
116.49 |
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N(3)C(4)H(4) |
121.89 |
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Methyl |
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C(5)C(6) |
1.4803 |
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C(6)H(7) |
1.0894 |
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C(6)H(8,9) |
1.0929 |
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C(5)C(6)H(7) |
109.64 |
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C(5)C(6)H(8,9) |
111.41 |
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H(8)C(6)H(9) |
107.62 |
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| Table 4. 5-Methyloxazole, trans. Atomic coordinates, ropt. |
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a (Å) |
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b (Å) |
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c (Å) |
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O(1) |
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0.0228 |
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1.0507 |
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C(2) |
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1.3173 |
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0.6639 |
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N(3) |
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1.5024 |
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0.6122 |
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C(4) |
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0.2168 |
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1.1316 |
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C(5) |
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0.6862 |
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0.1193 |
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H(2) |
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2.0543 |
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1.4508 |
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H(4) |
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0.0317 |
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2.1935 |
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C(6) |
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2.1639 |
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0.0332 |
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H(7) |
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2.5892 |
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1.0361 |
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H(8.9) |
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2.5328 |
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0.4964 |
± |
0.8820 |
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[1] E.R.L.Fliege, Z.Naturforsch. 45a,911(1990); E.Fliege, H.Dreizler, M.Meyer, K.Igbal, and J.Sheridan, Z.Naturforsch. 41a,623(1981). |
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Oxazole |
2-Methyloxazole |
4-Methyloxazole |
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Thiazole |
4-Methylthiazole |
5-Methylthiazole |
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Table of Contents
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Molecules/Nitrogen |
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5MeOxazole.html |
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Last
Modified 8 Nov 2003 |
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