Methyl fluoride: geometry

Figure 9.13 The geometry of some phosphorus chlorofluorides and some phosphorus methyl fluorides in which the larger and less electronegative ligands occupy the equatorial sites.

The molecular geometry of methane and of methyl fluoride is tetrahedral. In the case of methane, this symmetrical arrangement of polar covalent carbon-hydrogen bonds leads to a canceling of the bond polarities resulting in a nonpolar molecule. As a nonpolar molecule, the strongest intermolecular force in methane is a London force. In methyl fluoride, a fluorine atom replaces one of the hydrogen... 

These problems led Poirier et al.41 to re-investigate the relationship between the magnitude of the secondary a-deuterium KIE and transition state structure in SN2 reactions. The optimized geometries for the reactants and the transition structures for the Sn2 reactions where the nucleophile was F, Cl, OH, SH, NH2 or SCH3 and the substrate was either methyl fluoride or chloride were calculated at the HF/ 6-31+G level. Then, Sims BEBOVIB-IV program was used to carry out a... 

When refluxed for 15 h in xylene, aryl-substituted /V-(trimethylsilylmethyl)imines rearrange to /V-tri methyl si I y lazi ridines with high c/s-selectivity. It has been demonstrated that the reaction proceeds via an ylid that can be trapped with diethylacetylene-dicarboxylate (DEAD), for example. The more stable frans-geometry of the ylid and conrotatory cyclization would be responsible for the c/.v-aziridines. The authors note that no reaction occurs when the reaction is run in a polar solvent such as THF or acetonitrile, and that treatment of the imine with cesium fluoride in THF leads to protodesilylation only, as does 1 equiv. of water in HMPA.329... 

Lithium fluoride is able to promote the formation of azomethine ylids from /V-benzyl-/V-(met hox y met hy I)tri met h y I s i I y I met h y I am i ne. The reaction with methyl fumarate and maleate gives quantitative yields of trans and cis /V-benzyl-3,4-dicarbomethoxypyrro-lidines. Thus, the geometry of the alkenes is preserved during the cycloaddition reaction. These results are identical to those obtained using Achiwa s procedure (see Section VII.D.2). 

Similar behavior of the computation methods is found for nonidentity Sn2 reactions. The optimized geometries of the entrance and exit ion-dipole complexes (IDl and ID2) and TSs for Reaction 6.3-6.5 are shown in Figure 6.4. The entrance ion-dipole complex for Reaction 6.4 is nnnsual among the reactions discussed here. The ion-dipole complexes are characterized by the electrostatic interaction of the nncleophile with the most acidic hydrogen(s). In all of the other examples, the nncleophile associates with the methyl protons, bnt in 4-IDl, the most acidic proton is the alcohol hydrogen, so fluoride forms a hydrogen bond to it. For all three reactions, the TS displays the normal 8 2 features, namely, backside attack of the nucleophile accompanied by Walden inversion. They differ in how symmetric the... 

In the complex anion of a 1 1 complex, one Lewis acid R3AI is coordinated to the Lewis base, i. e., the fluoride anion. In the complex anion of a 1 2 complex on the other hand, two R3AI units are coordinated to the fluoride anion. The crystal structures of two of the 1 2 complexes of KF with R3AI are known, with R = Me and Et [5, 153). In both compounds, the fluorine atom is bound to two A1 atoms, the Al-F-Al angle equals 180°, and the Al-F bond length is 1.782 A in the methyl complex [118] and 1.820 A in the ethyl compound. The coordination geometry of A1 in both cases is tetrahedral, see Fig. 2. 

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