Related Experiment Video
Updated: Jun 2, 2026
07:50
Plasmid-derived DNA Strand Displacement Gates for Implementing Chemical Reaction Networks
Published on: November 25, 2015
Dynamic path bifurcation in the Beckmann reaction: support from kinetic analyses.
Yutaro Yamamoto1, Hiroto Hasegawa, Hiroshi Yamataka
1Department of Chemistry, Rikkyo University, Toshima-ku, Tokyo, Japan.
The Journal of Organic Chemistry
|May 14, 2011
Summary
The Beckmann rearrangement can fragment into carbocations and nitriles. This study shows path bifurcation after the rate-determining step, challenging traditional reactivity-selectivity theories in organic reactions.
Area of Science:
- Organic Chemistry
- Reaction Mechanisms
- Physical Organic Chemistry
Background:
- The Beckmann rearrangement converts oximes to amides.
- Fragmentation can occur, yielding carbocations and nitriles, especially with stable migrating groups.
- Previous molecular dynamics simulations suggested path bifurcation in this reaction.
Purpose of the Study:
- To investigate the Beckmann rearrangement and fragmentation pathways of oxime sulfonates.
- To determine the factors influencing the ratio of rearrangement to fragmentation products.
- To provide experimental evidence for the proposed path bifurcation mechanism.
Main Methods:
- Studied reactions of oxime sulfonates of 1-substituted-phenyl-2-propanone derivatives (7-X) and related substrates (8-X, 9a-X).
- Utilized aqueous acetonitrile (CH(3)CN) as the reaction medium.
- Analyzed product ratios (amides vs. alcohols) and reaction kinetics using logk-logk plots.
Main Results:
- Observed both amide (rearrangement) and alcohol (fragmentation) products.
- Product ratios varied significantly with the substrate: 7-X favored amides, while 9a-X favored alcohols.
- Logk-logk plots showed excellent linear correlations with slopes near unity, supporting a common intermediate or transition state.
Conclusions:
- The experimental results support path bifurcation occurring after the rate-determining transition state in the Beckmann rearrangement/fragmentation.
- This phenomenon may be more prevalent than previously assumed.
- Traditional reactivity-selectivity principles might not always apply to this textbook reaction, even after the rate-determining step.
Related Concept Videos
01:26Reaction Mechanisms: The Steady-State Approximation
The steady-state approximation, also referred to as the quasi-steady-state approximation to differentiate it from a true steady state, is a widely used method for simplifying calculations in complex reaction mechanisms. This approach is particularly useful when dealing with multi-step reactions that involve reverse reactions or several steps, which can significantly increase mathematical complexity and make the reactions nearly unsolvable analytically.The steady-state approximation operates on...
01:29Reaction Mechanisms: Rate-limiting Step Approximation
The rate-determining step, or RDS, in a chemical reaction is the slowest step that determines the overall reaction rate. It is identified by using the observed rate law and typically involves approximation methods like the RDS approximation or the steady-state approximation.In the RDS approximation, also known as the rate-limiting-step or equilibrium approximation, the reaction mechanism consists of one or more reversible reactions near equilibrium, followed by a slower RDS, and then one or...
02:31Multi-Step Reactions
Chemical reactions often occur in a stepwise fashion involving two or more distinct reactions taking place in a sequence. A balanced equation indicates the reacting species and the product species, but it reveals no details about how the reaction occurs at the molecular level. The reaction mechanism (or reaction path) provides details regarding the precise, step-by-step process by which a reaction occurs. Each of the steps in a reaction mechanism is called an elementary reaction. These...
03:06Reaction Mechanisms
Chemical reactions often occur in a stepwise fashion, involving two or more distinct reactions taking place in a sequence. A balanced equation indicates the reacting species and the product species, but it reveals no details about how the reaction occurs at the molecular level. The reaction mechanism (or reaction path) provides details regarding the precise, step-by-step process by which a reaction occurs.
For instance, the decomposition of ozone appears to follow a mechanism with two steps:
For instance, the decomposition of ozone appears to follow a mechanism with two steps:
01:34Woodward–Hoffmann Selection Rules and Microscopic Reversibility
Electrocyclic reactions, cycloadditions, and sigmatropic rearrangements are concerted pericyclic reactions that proceed via a cyclic transition state. These reactions are stereospecific and regioselective. The stereochemistry of the products depends on the symmetry characteristics of the interacting orbitals and the reaction conditions. Accordingly, pericyclic reactions are classified as either symmetry-allowed or symmetry-forbidden. Woodward and Hoffmann presented the selection criteria for...
01:29Chain Reactions
Chain reactions involve highly reactive transient species, such as atoms or free radicals, as intermediates. These intermediates facilitate rapid reactions over an extended period. The process includes a series of steps: a reactive intermediate is consumed, reactants are converted to products, and the intermediate is regenerated. This cycle enables continuous repetition, amplifying the production of products with a small amount of intermediate. Chain reactions often utilize free radicals as...