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Rules of the Day 11 - 3 O to drive the reaction back to the...

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Rules of the Day 2-13-09 1. Alkyl Wittig reagents give predominantly "Z" (cis) alkene products , while Wittig reagents with a carbonyl adjacent to the negative charge give predominantly "E" (trans) products . 2 . Protonation of a carbonyl oxygen atom in acid makes the carbonyl carbon atom much more electrophilic (i.e. able to react with weaker nucleophiles). 3. Alcohols are weak nucleophiles so they add to aldehydes/ketones with acid catalysis . Mechanism D is first part of mechanism. This mechanism is important! First one, then two alcohol molecules add to give hemiacetals and acetals, respectively. Only the acetal is thermodynamically more stable than the carbonyl species unless a cyclic hemiacetal is formed. These reactions are reversible by adding H
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Unformatted text preview: 3 O+ to drive the reaction back to the carbonyl compound and alcohols. 4. Diols can be used to create cyclic acetals . This usually confuses students although it is simply a special case of the same acetal reaction described above. 5. Protecting groups are chemical functions that can reversibly mask a reactive functional group to prevent an unwanted reaction. The protecting group is added prior to the reaction in question, then removed following the reaction in question. 6. Cyclic acetals are good protecting groups for use with Grignard reagents , since the cyclic acetals can be reversibly attached, and they have an sp3 carbon atom that won't react with nucleophiles like carbonyls do....
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