Download - SN1 SN2 MEXHANISM
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This workshop will address:
SN2 reactions
Break it down: what does it mean?
Rundown
Notes
SN1 reactions
Unimolecular: the main difference
Step-by-step Review: SN1 vs SN2
Resources
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The SN2 Reaction
Substrate
NucleophileLeaving Group
Product
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The SN2Reaction
SubstitutionNucleophilic
Bimolecular
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The SN2 Reaction
Nucleophilic:these reactions involve anucleophile (Nuc:-) replacing a leaving group.
Nucleophiles attack the substrate, donating an
electron pair to the new bond, and replacingthe leaving group (a substitution).
Tip: Remember the role of a nucleophile by its Greekroots: Nucleo-(nucleus)-phile-(lover) it is attracted tothe nucleus, which is positively charged! Nucleophiles aretherefore negatively charged or strongly -.
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The SN2 Reaction
Bimolecular:A bimolecular reaction is onewhose rate depends on the concentrations oftwoof its reactants.
SN2 reactions happen in one step thenucleophile attacks the substrate as theleaving group leaves the substrate.
Tip: Recall that the rate of a reaction depends on the
slowest step. In bimolecular reactions, therefore, the slowstep involves two reactants. For SN2 reactions, there areonly two reactants; this means that the slow step is theonlystep.
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The SN2 Reaction
Transition State
SN2 summary:(1) Nucleophile back-side attacks the + carbon center.
(2) Transition state forms in which nucleophile is forming bo(3) The leaving group leaves, forming the final product.
(1)(2)
(1) (3)
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The SN2 Reaction
Notes:In the SN2 reaction, the nucleophile attacks from the most + regioThis back-side attack causes an inversion(study the previous slide)The nucleophile must be able to reach the + carbon center that it i
Tip: see chapter 6 of your textbook to learn what makes a good nucleophile o
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The SN1 Reaction
CarbocationIntermediate
Substrate
Products
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The SN1Reaction
Substitution
NucleophilicUnimolecular
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The SN1 Reaction
SN1 reactions are nucleophilic substitutions, involving a
nucleophile replacing a leaving group (just like SN2).
However: SN1 reactions are unimolecular:the rate
of this reaction depends only on the concentrationof one reactant.
SN1 reactions happen in two steps:
1. The leaving group leaves, and the substrate forms acarbocation intermediate.
2. The nucleophile attacks the carbocation, forming the
product.
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The SN1 Reaction1. The Slow Step:
First step of the SN1 reaction:The leaving group leaves, and the substrate carbon now only has threCarbocations are most stable when there are more atoms to distributCarbocation stability:
3 > 2 >> 1Tip: study the difference between reaction intermediates and transition state
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The SN1 Reaction2. The Fast Step:
Second step of the SN1 reaction:The nucleophile attacks the carbocation intermediate, bringing its eleThe substrate loses any stereospecificity during the carbocation inte
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SN1 vs SN2 Reactions
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Resources
Chapter 6 of your textbook
The Khan Academy:
SN2 Reactions
SN1 Reactions
all organic chemistry topics
Organic Chemistry Portal
workshop created by Monica
All images used with permission under creative commons
http://www.khanacademy.org/video/sn2-reactions?topic=organic-chemistryhttp://www.khanacademy.org/video/sn1-reactions?topic=organic-chemistryhttp://www.khanacademy.org/http://www.organic-chemistry.org/namedreactions/nucleophilic-substitution-sn1-sn2.shtmhttp://www.organic-chemistry.org/namedreactions/nucleophilic-substitution-sn1-sn2.shtmhttp://www.organic-chemistry.org/namedreactions/nucleophilic-substitution-sn1-sn2.shtmhttp://www.khanacademy.org/http://www.khanacademy.org/http://www.khanacademy.org/video/sn1-reactions?topic=organic-chemistryhttp://www.khanacademy.org/video/sn1-reactions?topic=organic-chemistryhttp://www.khanacademy.org/video/sn2-reactions?topic=organic-chemistryhttp://www.khanacademy.org/video/sn2-reactions?topic=organic-chemistry