Nucleophile Addition of Grignard Reagents or Hydride to Carbonyls in Organic Chemistry

In this screencast, we examine the reactivity of the carbonyl group in a cyclic ester called a lactone. We are asked to predict the product given two different nucleophilic reagents. In P24, we are treating the lactone with an excess of phenyl magnesium bromide, a Grignard reagent. We know from electronegativity differences of atoms that Oxygen is more EN than Carbon. When C and O form a bond, the O has more electron density that the C. So in a carbonyl group, the carbon is electropositive. We can then predict that the Grignard reagent will add to the carbon atom. When this happens the carbonyl carbon changes hybridization from sp2 to sp3. Now tetrahedral, the carbon atom is able to collapse and rehybridize to spy as it has a good leaving group, an oxygen atom. After this happens, the carbonyl group becomes a ketone with a magnesium alkoxide at the chain terminus. We don't stop at this point however, the ketone carbonyl is actually more reactive than the lactone so it too undergoes a Grignard addition. Upon hybridization to sp3, there is no longer a good leaving group, so the carbon remains sp3, and ends up as a tertiary alcohol. In you like the video please subscribe for future updates!