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Related Concept Videos

SN1 Reaction: Stereochemistry02:15

SN1 Reaction: Stereochemistry

10.5K
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...
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Nucleophilic Aromatic Substitution: Addition–Elimination (SNAr)01:30

Nucleophilic Aromatic Substitution: Addition–Elimination (SNAr)

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Nucleophilic substitution in aromatic compounds is feasible in substrates bearing strong electron-withdrawing substituents positioned ortho or para to the leaving group. The reaction proceeds via two steps: the addition of the nucleophile and the elimination of the leaving group.
The reaction begins with an attack of the nucleophile on the carbon that holds the leaving group. This results in the delocalization of the π electrons over the ring carbons. The resonance interaction between...
4.8K
SN2 Reaction: Stereochemistry02:23

SN2 Reaction: Stereochemistry

11.9K
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...
11.9K
SN2 Reaction: Mechanism02:27

SN2 Reaction: Mechanism

17.6K
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...
17.6K
SN1 Reaction: Mechanism02:25

SN1 Reaction: Mechanism

14.5K
Kinetic studies of ionization of a tertiary halide in a protic solvent suggest that only the substrate participates in the rate-determining step (slow step). The nucleophile is involved only after the slowest step. The SN1 reaction takes place in a multiple-step mechanism. 
Firstly, the haloalkane ionizes to generate a carbocation intermediate and a halide ion. This heterolytic cleavage is highly endothermic with large activation energy. The ionization of the substrate, facilitated by a...
14.5K
Deindividuation00:57

Deindividuation

31.0K
Deindividuation is a form of social influence on an individual’s behavior such that the individual engages in unusual or non-normal behavior while in a group setting. Why? Because in these group settings, the individual no longer sees themselves as an individual anymore, disinhibiting their behavior and personal restraint.
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Related Experiment Video

Updated: Feb 16, 2026

Dissociation of the Confounding Influences of Expectancy and Integrative Difficulty Residing in Anomalous Sentences in Event-related Potential Studies
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The SNARC effect is not a unitary phenomenon.

Sara Basso Moro1, Roberto Dell'Acqua2,3, Simone Cutini4,5

  • 1Department of Neuroscience, University of Padua, Padua, Italy.

Psychonomic Bulletin & Review
|December 22, 2017
PubMed
Summary

The spatial-numerical association of response codes (SNARC) effect is not solely due to number representation or response selection. Our findings suggest a complex interplay influencing this cognitive phenomenon.

Keywords:
Magnitude comparisonNumerical distance effectSNARC effectSpatial–numerical associationsStimulus–response mapping

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Area of Science:

  • Cognitive Psychology
  • Neuroscience
  • Human Factors

Background:

  • The spatial-numerical association of response codes (SNARC) effect describes faster responses to small numbers with left effectors and large numbers with right effectors.
  • Current models diverge on whether the SNARC effect originates from the spatial nature of numerical representation or response selection dynamics.

Purpose of the Study:

  • To investigate the root cause of the SNARC effect by differentiating between semantic and response-related processing stages.
  • To test competing models of the SNARC effect by manipulating factors influencing both semantic and response selection.

Main Methods:

  • Developed a novel experimental paradigm combining magnitude comparison with stimulus-response (S-R) switching tasks.
  • Monitored SNARC effect modulations while concurrently assessing semantic and response-related processing.
  • Analyzed the nonlinear variation of the SNARC effect under manipulated experimental conditions.

Main Results:

  • The SNARC effect exhibited nonlinear modulations influenced by both magnitude comparison and S-R switching demands.
  • Observed significant interactions between numerical magnitude processing and response selection dynamics.
  • The observed nonlinearities challenge models positing a single, unitary cause for the SNARC effect.

Conclusions:

  • The SNARC effect likely arises from a complex interaction between numerical magnitude representation and response selection processes.
  • A unitary cause for the SNARC effect is insufficient to explain the observed data.
  • Future research should explore integrated models accounting for the dynamic interplay between semantic and motor factors.