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Reaction Mechanisms

Reaction 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:

Alkenes via Reductive Coupling of Aldehydes or Ketones: McMurry Reaction

Alkenes via Reductive Coupling of Aldehydes or Ketones: McMurry Reaction

The radical dimerization of ketones or aldehydes gives vicinal diols through a pinacol coupling reaction. However, the behavior of titanium metals used for the reaction as a source of electrons is unusual. When the reaction is carried out in the presence of titanium, diols can be isolated at low temperatures. Else titanium further reacts with diols, forming alkenes through the McMurry reaction.

Radical Reactivity: Intramolecular vs Intermolecular

Radical Reactivity: Intramolecular vs Intermolecular

Radical reactions can occur either intermolecularly or intramolecularly. In an intermolecular radical reaction, a nucleophilic radical adds to an electrophilic alkene or vice versa. In such reactions, the radical and generally the alkene, which is also called the radical trap, are two different molecules. Additionally, for such intermolecular reactions to occur, the radical trap must be active, present in an excess concentration, and the radical starting material must have a weak...

Cycloaddition Reactions: MO Requirements for Thermal Activation

Cycloaddition Reactions: MO Requirements for Thermal Activation

Thermal cycloadditions are reactions where the source of activation energy needed to initiate the reaction is provided in the form of heat. A typical example of a thermally-allowed cycloaddition is the Diels–Alder reaction, which is a [4 + 2] cycloaddition. In contrast, a [2 + 2] cycloaddition is thermally forbidden.

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Updated: Jun 23, 2025

Nanothermite with Meringue-like Morphology: From Loose Powder to Ultra-porous Objects

Nanothermite with Meringue-like Morphology: From Loose Powder to Ultra-porous Objects

Published on: December 24, 2017

Incomplete reactions in nanothermite composites.

Rohit J Jacob¹, Diana L Ortiz-Montalvo², Kyle R Overdeep³

¹Department of Chemical and Biomolecular Engineering and Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20706, USA.

Journal of Applied Physics

|June 21, 2024

Summary

This summary is machine-generated.

Nano-aluminum thermite reactions were forensically analyzed. Systems producing gaseous products showed higher reaction completion and smaller particles, indicating efficient redox reactions.

Keywords:

Nanothermite condensed phase focused ion-beam milling product analysis

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Reverse Microemulsion-mediated Synthesis of Monometallic and Bimetallic Early Transition Metal Carbide and Nitride Nanoparticles

Reverse Microemulsion-mediated Synthesis of Monometallic and Bimetallic Early Transition Metal Carbide and Nitride Nanoparticles

Published on: November 27, 2015

Area of Science:

Materials Science
Chemical Engineering
Combustion Science

Background:

Exothermic reactions between metals and metal-oxides are rapid, occurring on microsecond timescales.
Nanothermite systems offer unique combustion characteristics for study.
Understanding reaction extent is crucial for energetic material applications.

Purpose of the Study:

To investigate the reaction extent in nano-aluminum based thermite systems.
To analyze the product chemistry and morphology after rapid quenching.
To correlate combustion behavior with reaction completion.

Main Methods:

Ignition of microgram samples using resistive heating at high rates (10^5 K/s).
Rapid quenching of reaction products (≈ 500 microseconds).
Quantitative analysis via electron microscopy (EM), focused ion beam (FIB), and energy dispersive X-ray spectroscopy (EDX).

Main Results:

Elemental analysis revealed oxygen localized with aluminum, confirming redox reactions.
Al/CuO thermite showed lower oxygen content compared to Al/Bi2O3 and Al/WO3, correlating with gaseous oxygen release.
Smaller product particles exhibited higher oxygen content, suggesting greater reaction completion.

Conclusions:

Thermites generating significant gaseous products yield smaller particles and higher reaction completion.
Reaction mechanisms (gaseous vs. condensed phase) influence product characteristics.
Forensic analysis of quenched products provides insights into thermite reaction extent.