Concept · chemistry
Reaction mechanisms
Follow Reaction mechanisms — see important new research and changes in evidence.Change log
What changed
Dated edits to this page's evidence: studies added or removed from a claim, claims added or withdrawn, and new explanations tagged here. Rewordings are not listed.
- Concept page published
A reaction mechanism is the sequence of elementary steps, intermediates and transition states that convert reactants to products — tested by kinetics, isotopes, dynamics or computation against experiment.
Mechanism is how chemists explain why a reaction is fast, selective or fails — not just that it happened.
Evidence
What the evidence shows
Drawn from 6 studies in this library. Each finding starts with a plain-language takeaway, then the denser detail. Supports means evidence for a finding; Challenges means evidence against a stated position; Qualifies marks scope with a short note on each study’s contribution. Challenged positions are labeled — they are not findings.
This library holds 6 empirical chemistry papers on reaction mechanisms with isolated findings, rates or spectra rather than reviews.
Sensitive assays show microdroplet H2O2 comes from dissolved O2 reacting at solid–water interfaces, not from ultrahigh fields at the air–water surface.
FT-ICR and DFT show iron(IV)–oxo porphyrin cation radicals epoxidize olefins with rates that track substrate ionization energy.
Even with extra methyl groups on the alkyl iodide, Cl− and CN− still show a direct backward SN2 rebound channel at high collision energy rather than fully statistical dynamics.
DFT plus deuterium controls show (PhO)3PAu carbenes add at phenol para-C, then two waters shuttle the proton, beating O–H insertion.
Open questions
Tensions and limits
Some items are genuine disagreements on the same question. Others mark different assays, populations, or outcomes — limits on how far one study travels — not a forced fight between papers.
Computed pathways and experimental branching can disagree; a rate constant on one model substrate does not fix the mechanism of a catalytic cycle.
Study Role Design N Population Outcome H2O2 is not born at the air–water droplet surface Supports OtherLow-LOD H2O2 assays comparing bulk water, N2 condensates, humidifiers, and glass–water contacts Analytical chemistry controls — no sample N Bulk water, condensed microdroplets, and solid–water interfaces Whether spontaneous micromolar H2O2 forms at the air–water interface Gas-phase rates of heme-model olefin epoxidation Supports OtherGas-phase FT-ICR bimolecular rate constants for [FeIV(O)(TPFPP+·)]+ with olefins plus DFT Physical-organic kinetics panel of olefins — not a sample-N study Gas-phase iron-oxo porphyrin cation and olefin substrates Epoxidation rate constants and efficiency versus olefin ionization potential
Common misconceptions
If DFT finds a low barrier, that is the mechanism.
Computation is a hypothesis until it matches rates, isotopes or product ratios.
Exam-style questions
Short-answer questions that ask you to explain or compare, not recall.
What does reaction mechanisms mean in this chemistry library?
A reaction mechanism is the sequence of elementary steps, intermediates and transition states that convert reactants to products — tested by kinetics, isotopes, dynamics or computation against experiment.
Name one empirical finding from the reaction mechanisms papers.
Sensitive assays show microdroplet H2O2 comes from dissolved O2 reacting at solid–water interfaces, not from ultrahigh fields at the air–water surface.
What is a limit of reaction mechanisms evidence here?
Computed pathways and experimental branching can disagree; a rate constant on one model substrate does not fix the mechanism of a catalytic cycle.
The studies
6 studies in this library bear on Reaction mechanisms, ordered by citations.
- Gas-phase rates of heme-model olefin epoxidation
FT-ICR and DFT show iron(IV)–oxo porphyrin cation radicals epoxidize olefins with rates that track substrate ionization energy.
- H2O2 is not born at the air–water droplet surface
Sensitive assays show microdroplet H2O2 comes from dissolved O2 reacting at solid–water interfaces, not from ultrahigh fields at the air–water surface.
- Why gold carbenes hit phenol para-C–H
DFT plus deuterium controls show (PhO)3PAu carbenes add at phenol para-C, then two waters shuttle the proton, beating O–H insertion.
- Direct SN2 rebound survives bulky alkyl iodides
Even with extra methyl groups on the alkyl iodide, Cl− and CN− still show a direct backward SN2 rebound channel at high collision energy rather than fully statistical dynamics.
- Why acetaldehyde kills the DERA aldolase
Crotonaldehyde, the acetaldehyde aldol product, covalently bridges catalytic K167 to nearby C47; a C47M mutant survives 300 mM acetaldehyde.
- Ultrasound microdroplets make H2O2 from dissolved O2
Water-in-hexadecane droplets under 40 kHz ultrasound produce H2O2 at 0.24 mM min−1, almost entirely at the oil–water interface via superoxide from dissolved oxygen.
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