Term
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Definition
- constitutional isomers
- rapidly interconvertable
the keto is the most common at equilibrium (c=o) instea of enol (C=C-OH) |
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Term
| why does base-catalyzed enol formation work? |
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Definition
| hydrogens on alpha carbons are acidic, because the resultion anion is stabilized through resonance to end up on oxygen (the electronegative ion) |
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Term
| which is more reactive, an alkene or an enol? Why? |
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Definition
| the enol, because the oxygen lone pair can come down and donate electrons to the alpha carbon, making it more reactive |
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Term
| deuterium and reaction rate - use these to prove mechanism for alpha halogenation |
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Definition
1. reaction rate is shown to depend only on concentrations of acid and ketone, NOT on halogen (halogens not rate-limiting)
2. when put in deuterium, deuterium adds at a rate that's the same as the addition of the halogen, indicating the same intermediate is present |
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Term
| use molecular orbital theory to explain why the alpha carbon hydrogens are acidic |
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Definition
| when the alpha carbon anion p orbitals are oriented parallel to those of the carbonyl, the p orbitals overlap and the negative charge is shared by the electronegative oxygen atom |
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Term
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Definition
enol happens if you dip a keto in acid; enolate if you dip it in base.
- an enol is short-lived and non-isolatable |
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Term
| what is the problem with alpha substitution/enolate condensation and how do you fix it? |
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Definition
they happen in the same conditions (basic)
- for alpha substitution, use a STRONG base at a low temperature and add the alkyl halide very quickly
- for condensation, add catalytic amounts of a weak base |
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Term
| how do you overcome the infavorability of an aldol reaction? |
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Definition
| by removing the water after enone formation - this drives the reaction toward the product |
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Term
| why are enones so stable? |
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Definition
| they are conjugated - interaction between the pi electrons in the orbitals stabilize the molecule |
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Term
| what will give you a single product from a mixed aldol reaction? |
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Definition
| either have only one have alpha hydrogen (the donor); or have the donor have alpha hydrogens that are MUCH more acidic |
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Term
| why do amines have higher boiling points that similarly weighted alkanes? |
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Definition
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Term
| when is an amine water-soluble? |
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Definition
| when it has less than five carbons |
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Term
| which is the strongest base: RNH2, ROH, ROR? |
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Definition
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Term
| if the ammonium ion has a LARGE pKa, is the amine a strong or weak base? |
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Definition
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Term
| why are amides not strong bases? |
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Definition
| because it's resonance [or orbital] stabilized by the carbonyl group. |
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Term
| primary amine, secondary amine, tertiary amine, arylamine, heterocyclic amine - is this list in order of increasing or decreasing basicity? |
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Definition
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Term
| why are arylamines nonbasic? |
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Definition
| the nitrogen lone pair electrons are delocalized by the aromatic ring. this resonance stabilization is lost on protonation. |
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Term
| how does substituting an aniline affect its basicity? |
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Definition
| electron-donating groups like -CH3, -NH2, and -OCH3 make it MORE basic; electron-withdrawing groups make it LESS basic |
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Term
| what is a problem with using SN2 alkylation to form alkylamines? |
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Definition
| multiple alkylation - reaction won't stop at just one alkyl chain added |
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