Anionic Conditions (when a strong is involved) General principles review for strongly anionic/basic conditions apply In an anionic mechanism, a strong anion will drive the first step In an anionic mechanism, intermediates should positive charges Recognize anionic species even when they are disguised by a cationic metal counterion. Anionic additions to ketones Strong nucleophile required (R, H, HO, …) Intermediates have negative charge Addition first, protonation second Cationic Conditions (acid is involved) General principles review for acid/cartionic conditions apply Recipes that involve acid will be cationic In a cationic mechanism, the first step will routinely involve protonation In a cationic mechanism, the last step will frequently involve deprotonation to return to neutral Normally the main step or steps are sandwiched in between the protonation and deprotonation events Cationic additions to ketones Weak, neutral nucleophile involved (ROH, HOH…) Intermediates have positive charge Protonation addition second Weak nucleophile is not strong enough to add to neutral carbonyl Protonation activates the carbonyl as an electrophile A deprotonation step is routinely required following addition, to get back to neutral Addition is normally reversible Nucleophile can come back off Nucleophile is normally a reasonable leaving Buffer Conditions (both weak acid and weak base/nucleophile are present at same time) RNH2/H+, KCN/HCN… Reversibility again applies Whether addition before protonation, or protonation precedes addition depends on the exact case Anion Conditions: Nucleophilic addition versus deprotonation (enolate chemistry) Sometimes an will function as a base and remove a proton rather than functioning as a nucleophile and adding to the carbonyl Comparable to SN2 versus E2 reactions
Anionic Conditions (when a strong is involved) General principles review for strongly anionic/basic conditions apply In an anionic mechanism, a strong anion will drive the first step In an anionic mechanism, intermediates should positive charges Recognize anionic species even when they are disguised by a cationic metal counterion. Anionic additions to ketones Strong nucleophile required (R, H, HO, …) Intermediates have negative charge Addition first, protonation second Cationic Conditions (acid is involved) General principles review for acid/cartionic conditions apply Recipes that involve acid will be cationic In a cationic mechanism, the first step will routinely involve protonation In a cationic mechanism, the last step will frequently involve deprotonation to return to neutral Normally the main step or steps are sandwiched in between the protonation and deprotonation events Cationic additions to ketones Weak, neutral nucleophile involved (ROH, HOH…) Intermediates have positive charge Protonation addition second Weak nucleophile is not strong enough to add to neutral carbonyl Protonation activates the carbonyl as an electrophile A deprotonation step is routinely required following addition, to get back to neutral Addition is normally reversible Nucleophile can come back off Nucleophile is normally a reasonable leaving Buffer Conditions (both weak acid and weak base/nucleophile are present at same time) RNH2/H+, KCN/HCN… Reversibility again applies Whether addition before protonation, or protonation precedes addition depends on the exact case Anion Conditions: Nucleophilic addition versus deprotonation (enolate chemistry) Sometimes an will function as a base and remove a proton rather than functioning as a nucleophile and adding to the carbonyl Comparable to SN2 versus E2 reactions
Review%20of%20Organic%20Chem%20II.docx