What favours the hydride shift in the cannizaro's reaction? We know that hydride ion is a very poor leaving group then why does it shifr?
The Cannizzaro reaction takes place between carbonyl compounds without a hydrogen that can be abstracted by a strong base. Common examples are benzaldehyde and formaldehyde. The OH- ion acts as a nucleophile and attacks the carbonyl carbon, to form a tetrahedral intermediate. The most likely reaction of this intermediate is the reverse process: expulsion of hydroxide. The hydride (H-) is a less likely leaving group. Still, a hydride shift is observed when there is a second formaldehyde in the neighbourhood, to act as a hydride acceptor.