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Organic Chemistry
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- when attack takes place at chirality center, inversion of configuration takes place SN2
- R-O-R' -> (excess HBr or HI) gives R-X or R'-X, uses proton transfer then SN2
- the oxygen can be treated as a substituent (epoxy) on the parent alkane, use numbers to specify position
- convert more hindered alcohol into alkoxide, less hindered to its tosylate/alkyl halide, make sure tosylate/halide is a good SN2 substrate
- produces a strong alkylating reagent that can add an alkyl group to a variety of nucleophiles
- RONa (alkoxide), NaCN (cyanide), NaSH (sulfanide), RMgBr (grignard carbocation), LAH (hydride), could be H3O+, need water in a following step
- significant ring strain, so they have a great synthetic utility as intermediates
- thiols are more acidic than alcohols, conjugate base is more stable due to larger S compared to O (lower charge density)
- primary if primary vs secondary due to steric effect, tertiary if primary vs tertiary due to electronic effect
- even though they are generally not good leaving groups, the epoxide reaction is both kinetically (low Ea) and thermodynamically (products lower in energy) favored
- name the two alkyl groups attached to the oxygen and add the word ether, name groups in alphabetical order, if symmetrical use dialkyl or just alkyl
- ethers are relatively unreactive, so they are often ideal solvents, but they can be cleaved by heating concentrated HBr or HI
- at least one of the reagents (or catalyst) must be chiral, the Sharpless catalyst forms such a chiral complex with an allylic alcohol
- Br2 gives syn 3 membered ring with Br, water attacks more substituted carbon, deprotonation gives hydroxide, additional deprotonation gives an O electrophile, leaving group leaves and O binds to carbon that leaving group left
- hydroxide in an SN2 process opens the ring, resulting alkoxide ion protonated by water
- competing elimination with secondary alkyl halide or tosylate gives poor yields
- use mercury(II) acetate with alcohol solvent, alcohol will react with intermediate mercurinium ion by attacking the more substituted carbon
- relatively unreactive especially towards bases, except for epoxides and so are good solvents
- NaH over RX gives ether, deprotonating hydroxide, O anion attacks alkyl halide in SN2 reaction
- the acid-catalyzed dehydration of ethanol (proton transfer, SN2 attack, proton transfer), only good for primary alcohols and symmetrical ethers