Solutions to ProblemsChem 2204Part I (3)

Solutions to - H Initially all the water in the reaction is 18 O labelled and we form the hydrate that is 50 18 O labelled This species can give

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9/10/10 Problem: Explain why nucleophilic attack of the molecule on right is faster than molecule Assignment Hint : Obj10 C O Nu- . . . . Nu- C O MeO . . . . Nu- C O O 2 N . . . . slowe r faste r
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9/10/10 Solution: Nucleophilic attack of carbonyl involves formation of a tetrahedral intermediate (see template) . This step generally goes up uphill in energy since we are breaking a strong carbonyl bond . The MeO substituent stabilizes the starting material through resonance between the lone pairs on MeO oxygen and the carbonyl via the aromatic ring. This makes an uphill reaction even more unfavourable since the energy level of the starting material is lowered. Templa te Obj104 C O Nu- . . . . . . . . C O MeO . . . . C O N O O Energ y
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9/10/10 Explain how acetaldehyde can become O18-labelled by exposure to O18-labelled water Assignment Hint : H O H OH O O H 2 H H O H O O H 2 O H H excess + O = O 18 O = O 16
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9/10/10 H O H OH O
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Unformatted text preview: H Initially all the water in the reaction is 18 O labelled. . and we form the hydrate that is 50 % 18 O - labelled. This species can give either unlabelled or labelled starting material when the hydrate decomposes. + H 2 O- H 2 O H O H OH O H + H 2 O H O-H 2 O Because the 18 O labelled water is in great excess relative to acetaldehyde and the hydration reaction is freely reversible, eventually most of the acetaldehyde becomes 18 O labelled. Solution: 9/10/10 Draw a mechanism for the following transformation; Start by protonating on the carbonyl! Obj1 3 Assignment Templat e 9/10/10 Solution: Start by protonating on the carbonyl! O H O H CH 3 OH OCH 3 H + H O + H 2 O OH H H O O H OCH 3 O H H OH O H OH 2 O H CH 3 OH H-H + Proton transfer...
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This note was uploaded on 09/09/2010 for the course CHEM CHEM 2204 taught by Professor Peterbuist during the Summer '10 term at Carleton.

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Solutions to - H Initially all the water in the reaction is 18 O labelled and we form the hydrate that is 50 18 O labelled This species can give

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