CHEM 51C Lecture Notes - Lecture 2: Lithium Aluminium Hydride, Sodium Borohydride, Leaving Group
Document Summary
Review of activators and deactivators: activators: electron donating groups; puts electrons into the system, deactivators: electron withdrawing groups; pulls electrons away from system. Deactivating groups: most deactivating to least the carbonyl carbon= electrophilic site= good for nucleophilic attack. Some carbonyl compounds will have a more reactive electrophilic site, which can be determined by looking at the substituents. Acid chloride and acid anhydride have good leaving groups: cl= known as a good lg from 51a, rcoo-= resonance stability of leaving group makes it much easier to come off, pulling the electrons toward itself [not nucleophilic] Oh, -or, -nr2= known as poor leaving groups: highly activating groups. Lone pairs contribute to a smaller partial positive charge on the carbonyl carbon (sp2 hybridized with the empty p orbital: very nucleophilic/basic- less inclined to leave. Again, smaller partial positive charge on carbonyl carbon. With a partner or within your group, decide where ketones and aldehydes rank in terms of reactivity of the carbonyl.
