Theoretical
Study on Reaction Mechanism of Ground-State
Cyano Radical with 1,3-Butadiene: Prospect of Pyridine Formation
- Publication date
- Publisher
Abstract
The reaction of ground-state cyano
radicals, CN(X<sup>2</sup>Σ<sup>+</sup>), with the simplest
polyene, 1,3-butadiene (C<sub>4</sub>H<sub>6</sub>(X<sup>1</sup>A<sub>g</sub>)), is investigated to explore
probable routes and feasibility to form pyridine at ultralow temperatures.
The isomerization and dissociation channels for each of the seven
initial collision complexes are characterized by utilizing the unrestricted
B3LYP/cc-pVTZ and the CCSD(T)/cc-pVTZ calculations. With facilitation
of RRKM rate constants, through ab initio paths composed of 7 collision
complexes, 331 intermediates, 62 hydrogen atom, 71 hydrogen molecule,
and 3 hydrogen cyanide dissociated products, the most probable paths
at collision energies up to 10 kcal/mol, and thus the reaction mechanism,
are determined. Subsequently, the corresponding rate equations are
solved that the concentration evolutions of collision complexes, intermediates,
and products versus time are obtained. As a result, the final products
and yields are determined. The low-energy routes for the formation
of most thermodynamically stable product, pyridine, are identified.
This study, however, predicts that seven collision complexes would
produce predominately 1-cyano-1,3-butadiene, CH<sub>2</sub>CHCHCHCN
(<b>p2</b>) plus atomic hydrogen via the collision complex <b>c1</b>(CH<sub>2</sub>CHCHCH<sub>2</sub>CN) and intermediate <b>i2</b>(CH<sub>2</sub>CHCH<sub>2</sub>CHCN), with a
very minor amount of pyridine. Our scheme also effectively excludes
the presence of 2-cyano-1,3-butadiene, which has energy near-degenerate
to 1-cyano-1,3-butadiene, as supported by experimental findings