Quantum mechanics

Thermochemistry

Reaction rate constant

Catalysis

Linguistics

Philosophy

Pyrolysis

Photochemistry

Propene

Transition state

Substitution (logic)

Ab initio

Computer science

Kinetic isotope effect

Acetone

Physical chemistry

Thermodynamics

Physics

Organic chemistry

Deuterium

Substitution reaction

Computational chemistry

Kinetics

Propyne

Chemistry

Programming language

Ketene

Transition state theory

Journal of the American Chemical Society

The development of high-fidelity mechanisms for chemically reactive systems is a challenging process that requires the compilation of rate descriptions for a large and somewhat ill-defined set of reactions. The present unified combination of modeling, experiment, and theory provides a paradigm for improving such mechanism development efforts. Here we combine broadband rotational spectroscopy with detailed chemical modeling based on rate constants obtained from automated ab initio transition state theory-based master equation calculations and high-level thermochemical parametrizations. Broadband rotational spectroscopy offers quantitative and isomer-specific detection by which branching ratios of polar reaction products may be obtained. Using this technique, we observe and characterize products arising from H atom substitution reactions in the flash pyrolysis of acetone (CH3C(O)CH3) at a nominal temperature of 1800 K. The major product observed is ketene (CH2CO). Minor products identified include acetaldehyde (CH3CHO), propyne (CH3CCH), propene (CH2CHCH3), and water (HDO). Literature mechanisms for the pyrolysis of acetone do not adequately describe the minor products. The inclusion of a variety of substitution reactions, with rate constants and thermochemistry obtained from automated ab initio kinetics predictions and Active Thermochemical Tables analyses, demonstrates an important role for such processes. The pathway to acetaldehyde is shown to be a direct result of substitution of acetone's methyl group by a free H atom, while propene formation arises from OH substitution in the enol form of acetone by a free H atom.

Substitution Reactions in the Pyrolysis of Acetone Revealed through a Modeling, Experiment, Theory Paradigm