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33 Cards in this Set
- Front
- Back
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rate-determining step
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in a multistep mechanism, the step that requires the largest activation energy
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What affects the rate of the reaction?
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1. the larger the Ea, the slower the rxn
2. the higher the concentration of starting material, the faster the rxn 3. the higher the temp. the faster the rate |
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RATE EQUATION OF RXN
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rate = K [reactants]
K = rate constant [concentration of reactants] |
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How do catalysts work?
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- lower Ea
-does not effect product |
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VINYL HALIDE
do not under SN or E reactions because sp² hybridized |
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ARYL HALIDE
do not under SN or E reactions because sp² hybridized |
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best leaving group for halogens?
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iodine
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perfect electron deficient group?
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carbocations
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alkyl halides and Brønstead bases
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elimination rxn
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alkyl halides and nucleophiles
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substitution reactions
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as the size of the leaving group increases ( F < Cl < Br < I).....
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basicity decreases
(size increases down the column, basicity increases up the column) |
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What makes a better leaving group?
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A weaker base (which is a stronger acid)
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Nucleophilicity increases with...
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basicity
(from right to left on the periodic table) |
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What determines whether a nucleophile or a base?
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steric hinderance
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A molecule that has less steric hinderance
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is a stronger nucleophile and a weaker base
ex: ethoxide |
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A molecule with more steric hinderance
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is a weaker nucleophile and a stronger base
ex: tert-butoxide |
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e2 / sn2 rate equation
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rate eq = K [RX] [B/NU:]
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all sn2 reactions proceed with.....
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a back attack of the nucleophile, resulting in an inversion of configuration (inversion only when carbon being attacked is already a stereogenic center)
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rate determining step in sn2 mechanism
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formation of the carbonation (which is sp2 hybridized)
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what stabilizes a carbocation
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-INDUCTIVE EFFECT (alkyl chains donate e- via hyperconjugation)
-RESONANCE |
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in an endothermic rxn, what product is formed faster?
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the most stable product forms faster
(in exothermic, either or may form faster) |
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e1 / sn1 rate equation
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rate = K [RX]
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in an exothermic reaction, what is formed?
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the most stable product may or may not be formed faster (b/c the Ea in both cases is similar)
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polar protic solvents favor...
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SN1 & E1
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polar aprotic solvents favor...
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SN2 & E2
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What generally has a negative charge?
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bases and good nucleophiles
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Regioselective
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the rxn yields a CONSTITUTIONAL isomer predominantly or exclusively
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Stereoselective
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The rxn yields a STEREOISOMER predominantly or exclusively
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syn periplanar
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H & X on same side
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anti periplanar
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H & X on opposite sides
- E2 occurs via anti-periplanar elimination |
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How are alkynes prepared?
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Two successive elimination rxns
(geminal and vicinal dihalides) |
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geminal dihalide
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both halogens are on the same carbon
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vicinal dihalide
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the halogens are on opposite carbons
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