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O o o ome ome meo h meoh o o o oh meoh ome o purpose

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Unformatted text preview: with themselves as they exist mostly as the zwitterion. But after the acid is esterified it is much more electrophilic and the amino group is now nucleophilic. 5 6 Solutions Manual to accompany Organic Chemistry 2e NH3 R NH2 R CO2 CO2H NH3 EtOH HCl R NH2 base R CO2Et CO2Et The amine of one compound attacks the ester group of another to form a dimer (a peptide) which may cyclize to form a double amide, known as a diketopiperazine. The cyclisation is usually faster than the dimerization as it is an intramolecular reaction forming a stable six- membered ring. O O EtO NH2 R R HN NH2 OEt NH2 R CO2Et O R R HN NH R O O PROBLEM 6 It is possible to make either the diester or the monoester of butanedioic acid (succinic acid) from the cyclic anhydride as shown. Why does one method give the diester and one the monoester? O O O OMe OMe MeO H MeOH O O O OH MeOH OMe O Purpose of the problem An exploration of selectivity in carbonyl substitutions. Mechanistic thinking allows you to say confidently whether a reaction will happen or not. This problem builds on problem 2. Suggested solution In basic solution the nucleophile is methoxide ion. This strong nucleophile attacks the carbonyl group to give a tetrahedral intermediate having two possible leaving groups. The ester anion is preferred (pKa of RCO2H about 5) to t...
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