Rules of the Day 9

Rules of the Day 9 - 4 With some aldehydes and...

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Rules of the Day 2-9-09 1. The most important feature of carbonyl groups is that the carbon-oxygen double bond is highly polarized, with a partial positive charge on the carbon atom and a partial negative charge on the more electronegative oxygen atom. From this description alone it is clear that nucleophiles will attack the carbon carbon atom (while C=O pi bond breaks) and Lewis acids such as protons will react with the carbonyl oxygen atom. Time capsule: Strong base can remove a hydrogen on carbon atoms adjacent to carbonyl groups to give enolates. 2. Grignard reagents add to aldehydes and ketones to give tetrahedral alkoxide intermediates (can be isolated). These alkoxides are protonated when the chemist opens the flask and adds acid to give alcohols . Mechanism A . Carbon-carbon bond forming! 3. Aldehydes and Ketones connect to your 310M and roadmaps through alkenes (ozonolysis breaks C=C bond!) and oxidation of primary (PCC gives aldehydes) and secondary (PCC or H 2 CrO 4 gives ketones) alcohols.
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Unformatted text preview: 4. With some aldehydes and ketones (those without alpha hydrogens [stay tuned to find out what this means]), alkyl lithium reagents react like Grignards. Mechanism A . Carbon-carbon bond forming! However, for this class , you are better off using Grignards for reactions with aldehydes and ketones and alkyl lithium reagents as very strong bases . 5. The anions of terminal alkynes add to aldehydes and ketones to give tetrahedral alkoxide intermediates (can be isolated). These alkoxides are protonated when the chemist opens the flask and adds acid to give alkyne alcohols. Mechanism A . Carbon-carbon bond forming! 6. HCN is in equilibrium with H+ and CN-. CN- reacts with aldehydes and ketones to give a tetrahedral alkoxide intermediate that cannot be isolated becuase it is immediately protonated to give a cyanohydrin product . Mechanism A . Carbon-carbon bond forming! Time Capsule: Cyanohydrins are hydrolyzed in strong H 3 O+ to give α-hydroxy carboxylic acids....
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This note was uploaded on 09/22/2010 for the course CH 53200 taught by Professor Bocknack during the Spring '10 term at University of Texas.

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