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Pictures of the Day CH320M/CH328M Fall 2012

Epoxides - Reactions with Nucleophiles
Epoxides react with nucleophiles because this allows the opening of the three-membered ring and relief of ring strain (thus providing motive). In an epoxide such as the one shown above with different number of substituents on the carbons of the ring, strong nucleophiles like HO- will react predominantly on the backside of the less hindered carbon atom. In acid, a positively-charged intermediate analogous to a bromonium or mercurinium ion is produced. Reaction with nucleophiles such as H2O will occur at the more substituted carbon atom, because this is the one with more partial postive charge (blue color). Thus the regiochemistry can be controlled by choosing whether to use acid. Note that the sterochemistry of addition is anti in both cases (there is backside attack in both cases), leading to trans products.
The Functional Group Paradigm: Synthesis of Complex Molecules
Shown above are examples of chemistry you know being applied in very complex situations.The point is that functional groups such as the -OH group of alcohols or the pi bond of alkenes generally react the same whether they are in complex molecules such as those shown above, or in simple molecules like the ones we discuss most often in class. The functional group based approach to synthesis is a fundamental paradigm in organic chemistry, and it explains why the text book is organized around the different functional groups.