CARBONYL REDUCTIONS

There really are only 2 issues to remember with carbonyl reductions and they are outlined in the 2 equations on this post. First, the negatively charged hydride source (LAH or NaBH4) transfers hydride (H-) to the carbonyl carbon to give an oxygen anion which becomes protonated upon workup (not shown).
The second thing to remember is that when esters or acids are reduced, 2 equivalents of hydride (remember that only LAH will reduce these) are transfered to the carbonyl. The reason for this is that the initial, tetrahedral intermediate, is unstable. This gives an aldehyde which goes on to react with LAH. Don't get caught up in what the aluminum or boron species looks like...just think of these as simple nucleophile-electrophile or acid, base couplings and remember that the proton on the alcohol that results from these comes from water.