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The gas phase molecular structure of methyl vinyl ether at room temperature has been studied by joint analysis of electron diffraction and microwave data. Constraints on geometrical and thermal parameters were derived from the geometry and force field of the s-cis form, obtained by ab-initio calculations (4–21 G basis set) after complete geometry relaxation. A range of models was investigated that fits all available data (infrared, microwave and electron diffraction). The following rg/r-parameters were obtained: C=C: 1.337 Å, C(sp2)---O: 1.359 Å, C(sp3)---O: 1.427 Å, : 1.102 Å C=C---O : 127.3° and COC: 116.8°. Experimental rg---re (ab initio) corrections are given for C=C, C(sp2)---O and Csp3)---O.

This investigation demonstrates that molecular orbital constrained electron diffraction is sufficiently reliable and in such a manner that it can be applied to more complicated problems.  相似文献   

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The structure of tricyclo-(3.1.002,4)exane has been determined by gas phase electron diffraction. The molecule has an inversion centre. The mean carbon—carbon bond length, averaged over both three- and four-membered rings is 1.508 A. A model with equal C-C bond lengths fits to the measured diffraction intensities. The four-membered ring is planar with valency angles of 90°, while the carbon atoms of the three-membered rings form isosceles triangles. Ab initio quantum mechanical calculations at the STO-3G level support this geometry. The valency angle CCC (between three- and four-membered rings) for the equilateral four-membered ring model has been found experimentally to be 109.9°. The average C-H bond distance (1.080 Å) is small as a result of increased s-character in these bonds in agreement with reported INDO—LMO calculations.  相似文献   
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The molecular structure of cis- and trans-1,2-difluoroethene was studied in the gas phase by electron diffraction, using the sector-microphotometer technique. The molecules are planar. For trans-difluoroethene the geometrical parameters are: C-F bond: 1.338(0.003) Å; CC bond: 1.320(0.009) Å; C-H bond: 1.088(0.004) Å, ∠CCF 119.8°(0.2°); ∠CCH: 125° (1.2°). For cis-difluoroethene: C-F bond: 1.332(0.003) Å; CC bond: 1.311(0.008) Å; C-H bond: 1.100(0.003) Å; ∠CCF: 122.5°(0.2°); ∠CCH:127.0 °(2.3°).  相似文献   
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The structure and conformations of trans- and of cis-bicyclo[4.3.0]nonane have been studied in the gas phase. Molecular mechanics calculations applying the force field of Ermer and Lifson were used to obtain geometrical constraints, vibrational amplitudes and perpendicular vibrational corrections. The vibrational parameters were corrected for the large amplitude motion of the five-membered ring. The refinement for the trans-isomer confirms completely the predictions of the force field calculations. Although a stable solution could not be obtained for the cis-compound there is no contradiction between experiment and model calculations. The cyclohexane ring in both isomers is found to have a distorted chair conformation. In the cis-isomer it is flattened along the junction and more twisted in the other part. For the trans-compound the reverse is true.The following structural parameters rg, rα-structure) are put forward, (a) trans-compound: C2-symmetry, r(C-C)av = 1.536 Å. Average bond angle and average torsion angle in the cyclohexane ring are 110.2° and 58.1°, respectively. The connection angle, defined as the angle between the planes bisecting C6-C1-C5-C9 and C2-C1-C5-C4, is 180°. (b) cis-compound: no symmetry, r(C-C)av = 1.536 Å. Average bond and torsion angles in the cyclohexane ring are 112.2° and 52.3°, respectively. The connection angle is 124.8°.A comparison is made with structures of related compounds.  相似文献   
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