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Related Concept Videos

E1 Reaction: Stereochemistry and Regiochemistry02:43

E1 Reaction: Stereochemistry and Regiochemistry

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One of the critical aspects of the E1 reaction mechanism, as also observed in E2, is the regiochemistry, with multiple regioisomers obtained as products. In the example discussed, the presence of water as a weak base favors elimination over substitution to generate two alkenes. Given that alkenes’ stability increases with the number of alkyl groups across the double bond, typically, E1 reactions lead to the Zaitsev product, for this is more substituted and stable than the Hofmann product.
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E2 Reaction: Kinetics and Mechanism02:45

E2 Reaction: Kinetics and Mechanism

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SN2 substitutions and E2 eliminations of alkyl halides proceed via a concerted pathway. While the nucleophile attacks the alpha carbon in SN2 reactions, it functions as a strong base and abstracts a beta hydrogen in the E2 mechanism. The rate-limiting transition state in E2 elimination reactions is characterized by partially broken carbon–hydrogen and carbon–halogen bonds and a partially formed pi bond between the alpha and beta carbons. The beta hydrogen and halide are eliminated...
10.2K
E1 Reaction: Kinetics and Mechanism02:46

E1 Reaction: Kinetics and Mechanism

14.5K
Here, in contrast to the E2 reaction mechanism, we delve into the aspects of the E1 reaction mechanism, which has two steps: rate-limiting loss of the leaving group and abstraction of the beta hydrogen by a weak base. Typically, the experimental proof for the E1 mechanism is via kinetic studies or isotope studies. While the former demonstrates the first-order kinetics—the dependence of the reaction solely on substrate concentration—the latter proves the abstraction of hydrogen only...
14.5K
E2 Reaction: Stereochemistry and Regiochemistry02:43

E2 Reaction: Stereochemistry and Regiochemistry

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Elimination reactions of alkyl halides can yield one or more alkenes depending on the specific regiochemical and stereochemical considerations. While the regiochemistry of the reaction governs the location of the double bond in the product, the stereochemical requirements often influence the geometry.
When a substrate with two different β hydrogens undergoes an E2 elimination, the presence of a strong base can yield two regioisomeric alkenes. The more-substituted alkene is the major...
11.5K
Elimination Reactions02:25

Elimination Reactions

13.6K
A nucleophile can react with an alkyl halide to give the substitution product by displacing the halogen. Or it can function as a base to give the elimination product by deprotonation of the neighboring carbon to form an alkene. In an elimination reaction, the substrate loses two groups from adjacent carbons forming at least one π bond. The carbon attached to the halogen is called the α carbon, while the adjacent carbon is called the β carbon; hence, these reactions are called...
13.6K
Amines to Alkenes: Hofmann Elimination01:16

Amines to Alkenes: Hofmann Elimination

2.4K
Alkenes can be obtained from amines via an E2 elimination. The amine is first converted into a good leaving group, such as a quaternary ammonium salt. This is accomplished by treating the amine with an excess of alkyl halide, which results in a halide salt. Next, the halide salt is transformed into a hydroxide salt that functions as a base to enable elimination.
Under thermal conditions, the hydroxide can abstract a proton from the β carbon; this generates an alkene with the simultaneous...
2.4K

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Size effects in ion-neutral complex-mediated alkane eliminations from ionized aliphatic ethers.

D J McAdoo1, C E Hudson, J C Traeger

  • 1Marine Biomedical Institute, University of Texas Medical Branch, 200 University Eoulevard, 77550, Galveston, TX.

Journal of the American Society for Mass Spectrometry
|November 19, 2013
PubMed
Summary

The size of ionic and neutral partners influences alkane elimination in ionized ethers. Larger ionic partners decrease alkane elimination, while larger neutral partners increase it by enhancing attraction within ion-neutral complexes.

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Area of Science:

  • Physical Chemistry
  • Chemical Dynamics
  • Mass Spectrometry

Background:

  • Ion-neutral complex-mediated reactions are crucial in chemical processes.
  • Aliphatic ethers undergo various fragmentation pathways upon ionization.
  • Understanding factors influencing these pathways is key to predicting chemical behavior.

Purpose of the Study:

  • To investigate how the size of ionic and neutral partners affects alkane elimination.
  • To elucidate the role of intermolecular forces in ion-neutral complex-mediated reactions.
  • To quantify the impact of partner size on reaction competitiveness.

Main Methods:

  • Metastable decomposition spectroscopy was employed.
  • Photoionization efficiency curves were obtained.
  • Analysis focused on competition between alkane elimination and alkyl loss.

Main Results:

  • Increasing ionic partner size reduced alkane elimination relative to alkyl loss.
  • Increasing neutral partner size lowered the alkane elimination threshold.
  • Enhanced attraction was observed with increased neutral partner polarizability.

Conclusions:

  • Partner size significantly modulates ion-neutral complex-mediated alkane elimination.
  • Intermolecular attraction, influenced by partner size and polarizability, governs reaction outcomes.
  • Specific structural changes, like adding a CH2 group, predictably alter attraction.