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Chapter 23 Mech/Con
| Question | Answer |
|---|---|
| Enol Keto Exceptions | Usually, the keto is more favored than the enol, but there's certain scenarios like when the intramolecular hydrogen bonds are there or the bonds are conjugated or there's the resonance of a benzene that up the yield. |
| Draw the General Formula of Carbonyl and Enolate Reactions | Enolate ion attacks and attaches to the carbonyl. |
| Draw the Mechanism for Base Catalyzed Aldol | Uses a base reagent like KOH, H2O or NaOH, H2O, EtOH. The end result is a b-hydroxy aldehyde (an aldol). The carbonyl on the enolate will stay the same but the one on the electrophile will become an alcohol. |
| Draw the Mechanism for Acid Catalyzed Aldol | Use an acidic reagent. First make an protonated enolate to work with then, perform the usual aldol steps except start with protonation first. |
| Aldol Indicator Tip | If you see any aldehydes, that's a potential indicator that you'll be working with aldol. |
| Draw the Mechanism for Basic Aldol Condensation | The product of aldol reaction is not stable; upon warming with base, they eliminate H2O to form a,b-unsaturated aldehydes or ketones. |
| Draw the Mechanism for Ec1B (elimination unimolecular 1 conjugate base) | Helps you go from your aldol product to your a,b unsaturated product. Just two steps. |
| Draw the Mechanism for Acidic Aldol Condensation | Make your aldol and then go through a very unecessarily complicated mechanism to get your a,b unsaturated product. |
| Aldol Product Tip | If there's heat involved after the regular aldol reagents, there's a good chance they're asking for the full equation with the elimination involved. |
| Draw the Mechanism for Retroaldol Reaction | The aldol product is unstable so depending on the circumstances, it can either undergo elimination or retroaldol - cleaving itself to make the original aldehyde or ketone. Occurs more readily when an and b are sterically hindered. WATCH MORE VIDEOS |
| Draw the Mechanism for Crossed-Aldol Reactions | Similar to aldol, except you have two enolizable aldehydes or ketones. You make an enolate out of one - usually the less substituted one - and performed the reaction. |
| Kinetic Enolate Vs. Thermodynamic Enolate | With kinetic, elimination is faster than the aldol or retroaldol process. With thermodynamic, the retroaldol process is faster than the elimination. |
| Draw the Mechanism of Directed Aldol Reactions (A Variation of Crossed Aldol) | If both reactants have a-hydrogens, an enolate can be generated from one of the reactant in an anhydrous aprotic solvent like pentane, THF, DMSO, etc, with one SB like LDA or BuLi, then other reactant is added. Essentially, one end will be OH other OR. |
| Draw the General Formula of Intramolecular Aldol Condensation | Product is a cyclic a, b unsaturated ketone or aldehyde. Formation of five or six membered ring is favored - essentially, aldol (KOH, H2O or NaOH, H2O, heat) but you're closing a ring. |
| Draw the Mechanism of Claisen Condensation | Claisen condensation is a reaction between an ester enolate and the parent ester, forming a b- keto ester. |
| Claisen Condensation Equilibrium Tips | In the first step, the equilibrium lies to the left because the parent ester is the weaker acid. Near the end, like step four, it's to the right to facilitate the end. Claisen needs full equiv of base, 1 molecule base consumed for 2 molecules of ester. |
| Draw the Mechanism for Retro Claisen | If there's an ester with only 1 a-H instead of multiple, you have to do retro claisen. It has the same first steps but the acid-base step does not occur because there is no proton in between the carbonyls. Instead the ketone C atom is most electrophilic. |
| Draw the Mechanism for Preparing a b-Keto Ester for Retro Claisen | The ester is completely converted to its enolate with one equivalent of strong base (LDA, -78 C), the enolate reacts with acyl chloride to make ketone portion of the product. |
| Draw the Mechanism for the Dieckmann Condensation (Intramolecular Claisen Condensation) | A diester can undergo an intramolecular Claisen condensation called the Dieckmann cyclization, which is an excellent method to make ketones and their derivations. Same exact mechanism as regular Claisen, 5 to 6 rings significantly favored. |
| Draw the Mechanism for Crossed-Claisen Condensation | A reaction between two different esters. Specifically a reaction between an enolate ion and an ester (or acid chloride). Reaction works best when there's no proton alpha to carbonyl group, so benzoate, formate, and oxalate esters are good substrates. |
| Crossed-Claisen Tips | When the product has a proton attached to the C atom between the carbonyl groups, the product has acid-base step. Therefore, you need 2 equiv of the enolate and acid base step. ALSO if there's an ketone & ester, use ketone enolate cause more acidic. |
Created by:
smurtab