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2-CH3-C5H4N
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PDF, trans
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Nitrogen
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Nuclear
Quadrupole Coupling Constants |
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in
2-Methylpyridine |
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Nitrogen nqcc's in 2-methylpyridine
were first determined in 1970 by Dreizler et al. [1], and revisited in
2004 by Wörmke et al. [2] using a high resolution FTMW
spectrometer. |
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Assuming Cs symmetry for
2-methylpyridine, one methyl CH bond lies in the plane of the pyridine
ring. Calculation of the nitrogen nqcc's was made here on
B3P86/6-31G(3d,3p) optimized molecular structures corresponding to each
of two possible orientations of the methyl group, the in-plane CH bond
being either trans or cis with respect to the
nitrogen atom. |
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The calculated nqcc's are compared in
Tables 1 and 2 with the experimental nqcc's of Wörmke et al.
[2]. Structure parameters for the lower-energy trans
conformer are compared with those for pyridine in Table 3.
Atomic coordinates for the trans conformer are given in
Table 4, rotational constants in Table 5. |
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Etrans < Ecis
by 0.16 kcal/mol calculated at the B3P86/6-31G(3d,3p) level of theory,
and 0.27 kcal/mol at the B3PW91/6-311+G(df,pd) level. |
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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
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 differene
between calculated and
experimental nqcc's (percent of average experimental nqcc). RSD
is the calibration residual standard deviation 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
2-Methylpyridine, trans (MHz).
Calculation
was made on the B3P86/6-31G(3d,3p) ropt structure. |
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Calc. |
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Expt. [2] |
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14N |
Xaa |
- |
0.352 |
- |
0.35 * |
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Xbb |
- |
2.854 |
- |
2.87 * |
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Xcc |
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3.207 |
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3.22(1) |
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|Xab| |
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2.893 |
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2.38(14) |
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RMS |
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0.012 (0.56 %) |
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RSD |
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0.030 (1.3 %) |
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Xxx |
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1.548 |
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1.1(12) |
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Xyy |
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3.207 |
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3.223(8) |
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Xzz |
- |
4.755 |
- |
4.3(12) |
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ETA |
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0.349 |
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Øz,a |
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56.69 |
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Øa,bi |
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57.26 |
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Øz,bi ** |
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0.57 |
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* Calculated
here from Xcc and Xaa - Xbb =
2.52(1) MHz. |
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** The z-axis makes an angle of
0.57o with the external bisector ( 'bi' ) of the
C(6)N(1)C(2) angle, and tilts toward C(2). |
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Table 2. Nitrogen nqcc's in
2-Methylpyridine, cis (MHz).
Calculation
was made on the B3P86/6-31G(3d,3p) ropt structure. |
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Calc. |
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Expt. [2] |
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14N |
Xaa |
- |
0.346 |
- |
0.35 * |
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Xbb |
- |
2.892 |
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2.87 * |
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Xcc |
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3.238 |
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3.22(1) |
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|Xab| |
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2.875 |
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RMS |
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0.016 (0.77 %) |
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RSD |
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0.030 (1.3 %) |
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* Calculated
here from Xcc and Xaa - Xbb =
2.52(1) MHz. |
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| Table 3.
2-Methylpyridine, trans
and Pyridine. Molecular structure parameters, ropt
(Å and degrees). |
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2-Me-Pyridine |
Pyridine |
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N(1)C(2) |
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1.3391 |
1.3336 |
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C(2)C(3) |
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1.3952 |
1.3904 |
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C(3)C(4) |
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1.3879 |
1.3885 |
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C(4)C(5) |
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1.3875 |
1.3885 |
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C(5)C(6) |
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1.3900 |
1.3904 |
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C(6)N(1) |
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1.3310 |
1.3336 |
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C(3)H(3) |
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1.0849 |
1.0845 |
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C(4)H(4) |
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1.0853 |
1.0851 |
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C(5)H(5) |
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1.0841 |
1.0845 |
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C(6)H(6) |
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1.0884 |
1.0880 |
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C(6)N(1)C(2) |
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118.05 |
117.03 |
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N(1)C(2)C(3) |
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122.08 |
123.80 |
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C(2)C(3)C(4) |
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119.26 |
118.44 |
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C(3)C(4)C(5) |
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118.74 |
118.50 |
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C(4)C(5)C(6) |
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117.94 |
118.44 |
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C(5)C(6)N(1) |
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123.93 |
123.80 |
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C(2)C(3)H(3) |
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119.96 |
120.21 |
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C(3)C(4)H(4) |
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120.49 |
120.75 |
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C(4)C(5)H(5) |
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121.57 |
121.35 |
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C(5)C(6)H(6) |
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120.23 |
120.26 |
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C(2)C(7) |
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1.4999 |
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C(7)H(8) |
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1.0914 |
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C(7)H(9,10) |
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1.0932 |
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N(1)C(2)C(7) |
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116.26 |
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C(2)C(7)H(8) |
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111.83 |
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C(2)C(7)H(9,10) |
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110.28 |
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| Table 4.
2-Methylpyridine, 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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N(1) |
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0.3082 |
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1.1625 |
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C(2) |
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0.9013 |
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0.0382 |
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C(3) |
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0.1695 |
- |
1.2260 |
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C(4) |
- |
1.2172 |
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1.1685 |
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C(5) |
- |
1.8333 |
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0.0747 |
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C(6) |
- |
1.0221 |
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1.2035 |
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H(3) |
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0.6855 |
- |
2.1804 |
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H(4) |
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1.8061 |
- |
2.0801 |
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H(5) |
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2.9128 |
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0.1731 |
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H(6) |
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1.4658 |
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2.1973 |
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C(7) |
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2.4012 |
- |
0.0376 |
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H(8) |
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2.8074 |
- |
1.0506 |
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H(9,10) |
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2.7798 |
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0.4920 |
± |
0.8782 |
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| Table 5.
2-Methylpyridine, trans.
Rotational Constants (MHz). |
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Calc ropt |
Expt [2] |
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A |
5740.8 |
5696.005(2) |
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B |
2648.6 |
2632.546(2) |
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C |
1832.9 |
1820.451(1) |
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[1] H.Dreizler, H.D.Rudolph,
and H.Mäder, Z.Naturforsch. 25a,25(1970). |
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[2] S.Wörmke, K.Brendel,
U.Andresen, and H.Mäder, Mol.Phys. 102,1625(2004). |
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Pyridine |
3-Methylpyridine |
4-Methylpyridine |
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2-Fluoropyridine |
2-Chloropyridine |
2-Bromopyridine |
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2,6-Lutidine |
2-Cyanopyridine |
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2-Pyridine-Carbaldehyde |
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Table of Contents
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Molecules/Nitrogen |
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2MePYR.html |
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Last
Modified 30 Dec 2007 |
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