Ab initio investigations of the rearrangements of some sodium β-halo alkoxides via G3 calculations

Abstract EN

G3 conformational analysis of anhydrous and hydrated sodium β-haloalkoxides reveals that the g+ and g- conformers are more stable than the anti-one by about 6-7 kcal / mol.

The transition State, TS g+, g- requires less activation energy than those necessary for the formation of TS g+, anti and TS g-, anti.

The possible rearrangement for the anti-conformers is the formation of the epoxides with an intra-molecular SN2 mechanism.

These rearrangements are not feasible as those for the free alkoxides because the oxygen of the free alkoxides has almost a complete negative charge.

The rearrangements of g+ and g- conformers to carbonyl compounds are feasible via SN1 mechanism through the formation of either Me- or H-bridged carbocations depending on the structure of the substrate.

Me-bridged TS requires higher activation energy.

The presence of water in the hydrated alkoxides has approximately no effect on the conformational Eact values.

However, the presence of water increases the Eact values for the rearrangement processes by about 2-3 kcal / mol.

The obtained results lead to a conclusion that the preferred conformers are g+ and g- ones and their rearrangements to carbonyl compounds are the most likely to take place either in anhydrous or hydrated sodium β-haloalkoxides.