sn1 sn2 mexhanism

8/12/2019 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

sn1 sn2 mexhanism

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