Walden inversion double

LXIII), the trans nucleoside (LXVI) would arise by way of a double Walden inversion by either of two mechanisms. Inversion of LXIII to... 

CCI4, deprotonates the alcohol. The alcoholate 56 attacks the phosphorous atom of 54 and thereby liberates the chloride ion which then attacks the stereogenic center from the side opposite to the nucleofugal group. This mechanism leads to a complete Walden inversion. The 0=P double bond is very stable, compensating the energy demand of the C-O bond cleavage. 

The energy along the reaction path has a double-well shape, with two symmetrical minima that are due to the strong ion-molecule polarization force and a central barrier to atom exchange. The structme at the barrier corresponds to a planar CH3 group. The reaction therefore proceeds through a Walden inversion, Figme 5.21. 

The central barrier in the double-minimum potential energy profile, a Walden-inversion transition state, may lie above or below the initial energy of the reactants. The rate coefficients for 5 2 reactions show a slight negative temperature dependence. 

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