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Author(s):   Guner, V.; Khuong, K.S.; Leach, A.G.; Lee, P.S.; Bartberger, M.D.; Houk, K.N.
Title:   A standard set of pericyclic reactions of hydrocarbons for the benchmarking of computational methods: The performance of ab initio, density functional, CASSCF, CASPT2, and CBS-QB3 methods for the prediction of activation barriers, reaction energetics, and transition state geometries
Journal:   J. Phys. Chem. A
Volume:   107
Page(s):   11445 - 11459
Year:   2003
Reference type:   Journal article
Squib:   2003GUN/KHU11445-11459

Reaction:   Cyclobutene1,3-Butadiene
Reaction order:   1
Rate expression:   no rate data available
Category:  Theory
Data type:   Ab initio
Comments:   No rate constants reported. Quantum calculations of energetics of pericyclic reactions. Calculated structures and energies of reactants, products, and transition states. Report activation energies and entropies of activation, thus rate expressions could be derived from them, albeit only at 298 K. Used a variety of methods DFT (density functional theory) such as B3lYP/ BPW91, and MPW1K and ab initio methods including MP2, CBS-QB3, and CASPT2. Employed basis sets 6-31G(d), 6-31+G(d,p),, and 6-311G. Corrected energies using ZPEs and thermal contributions from 298 to 0 K. Assumed harmonic frequencies. Low frequency inversion and other ring modes considered to be harmonic, thus may affect the thermal correction some. Similarly the few reactions having free rotors were treated as harmonic vibrations and this may affect thermal correction a bit. For most of the methods the deviations were on the order of 2-5 kcal/mol for activation energies.

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