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Related Concept Videos

Predicting Products: SN1 vs. SN202:27

Predicting Products: SN1 vs. SN2

13.8K
Nucleophilic substitution reactions of alkyl halides can proceed via an SN1 or an SN2 mechanism. While in SN2 reactions, the nucleophile attacks the substrate simultaneously as the leaving group departs, in SN1 reactions, the substrate first dissociates to give the carbocation intermediate. Various factors such as the structure of the substrate, the strength of the nucleophile, and the nature of the solvent promote one mechanism over the other.
With increased substitution on the alkyl halide,...
13.8K
SN2 Reaction: Mechanism02:27

SN2 Reaction: Mechanism

14.7K
The kinetic studies of SN2 reactions suggest an essential feature of its mechanism: it is a single-step process without intermediates. Here, both the nucleophile and the substrate participate in the rate-determining step.
The presence of the more electronegative halogen in the substrate creates a polarized carbon-halide bond. The halide pulls the electron cloud generating an electrophilic center at the carbon atom. Thus, the carbon atom carries a partial positive charge while the halide has a...
14.7K
SN2 Reaction: Transition State02:26

SN2 Reaction: Transition State

10.1K
An SN2 reaction of an alkyl halide is a single-step process in which bond formation between the nucleophile and the substrate and bond breaking between the substrate and the halide occurs simultaneously through a transition state without forming an intermediate.
When the nucleophile approaches the electrophilic carbon with its lone pairs, the halide acts as a leaving group and moves away with the electron-pair bonded to the carbon. Dotted partial bonds represent the bonds being formed or broken...
10.1K
SN2 Reaction: Stereochemistry02:23

SN2 Reaction: Stereochemistry

9.8K
In an SN2 reaction, the nucleophilic attack on the substrate and departure of the leaving group occurs simultaneously through a transition state. As the nucleophile approaches the substrate from the back-side, the configuration of the substrate carbon changes from tetrahedral to trigonal bipyramidal and then back to tetrahedral, leading to an inversion in the configuration of the product.
If the substrate is an achiral molecule at the α-carbon, the inversion of configuration is not...
9.8K
SN2 Reaction: Kinetics02:14

SN2 Reaction: Kinetics

8.7K
Kinetic Studies and Significance
In a chemical reaction, a relationship exists between the concentration of reactants and the rate at which the reaction proceeds. The study to measure this relationship is known as the kinetics of a chemical reaction. Kinetic studies are used to deduce the rate law of a chemical reaction, which provides information about the species involved during the transition state of the rate-determining step. Thus, kinetic studies help to derive the mechanism of a...
8.7K
SN1 Reaction: Stereochemistry02:15

SN1 Reaction: Stereochemistry

8.8K
This lesson provides an in-depth discussion of the stereochemical outcomes in an SN1 reaction.
In the first step of an SN1 reaction, the bond between the electrophilic carbon and the leaving group ionizes to generate the carbocation intermediate. The second step of the mechanism is the nucleophilic attack.
In the formed carbocation, the positively charged carbon is sp2 hybridized with a trigonal planar geometry. As all the three substituents lie on the same plane, a plane of symmetry for the...
8.8K

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Related Experiment Video

Updated: Sep 6, 2025

The Synthesis of [Sn10SiSiMe334]2- Using a Metastable SnI Halide Solution Synthesized via a Co-condensation Technique
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The Synthesis of [Sn10SiSiMe334]2- Using a Metastable SnI Halide Solution Synthesized via a Co-condensation Technique

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SN2 versus SN2' Competition.

Thomas Hansen1,2,3, Pascal Vermeeren1, Lea de Jong1

  • 1Department of Theoretical Chemistry, Amsterdam Institute of Molecular and Life Sciences (AIMMS), Amsterdam Center for Multiscale Modeling (ACMM), Vrije Universiteit Amsterdam, De Boelelaan 1083, 1081 HV Amsterdam, The Netherlands.

The Journal of Organic Chemistry
|June 24, 2022
PubMed
Summary
This summary is machine-generated.

This study explores nucleophilic substitution reactions, explaining when a nucleophile attacks directly (SN2) or rearranges (SN2'). Activation strain analysis reveals key factors governing this competition in organic synthesis.

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Area of Science:

  • Physical Chemistry
  • Organic Chemistry
  • Computational Chemistry

Background:

  • Bimolecular nucleophilic substitution reactions are fundamental in organic synthesis.
  • Allylic systems present a competition between direct (SN2) and rearranged (SN2") pathways.

Purpose of the Study:

  • To quantum chemically explore the SN2 vs. SN2' competition for allylic systems.
  • To develop a physically sound model for predicting reaction pathways.
  • To identify underlying factors governing reactivity trends.

Main Methods:

  • Combined relativistic density functional theory (DFT) and coupled-cluster theory.
  • Activation strain analyses to probe reaction mechanisms.
  • Exploration of halogen leaving groups (F, Cl, Br, I).

Main Results:

  • Detailed analysis of the SN2 and SN2' reaction pathways for various nucleophiles and allylic substrates.
  • Identification of 'characteristic distortivity' and 'transition state acidity' as key factors.
  • Demonstration of these concepts as predictive tools for reactivity.

Conclusions:

  • The study provides a robust model for understanding and predicting SN2/SN2' competition in allylic substitution.
  • Activation strain analysis effectively elucidates the physical drivers of reaction selectivity.
  • The findings offer valuable insights for designing synthetic strategies and optimizing reaction outcomes.