Theoretical Study on Reaction Mechanism of Ground-State Cyano Radical with 1,3-Butadiene: Prospect of Pyridine Formation

Abstract

The reaction of ground-state cyano radicals, CN(X(2)Σ(+)), with the simplest polyene, 1,3-butadiene (C4H6(X(1)Ag)), 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, CH2CHCHCHCN (p2) plus atomic hydrogen via the collision complex c1(CH2CHCHCH2CN) and intermediate i2(CH2CHCH2CHCN), 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.

Synthesis and Characterization of Cyanobutadiene Isomers—Molecules of Astrochemical Significance

“…Spectroscopic data for the organic nitriles described herein( E )-1-cyano-1,3-butadiene ( E -1 ), ( Z )-1-cyano-1,3-butadiene ( Z -1 ), 4-cyano-1,2-butadiene ( 2 ), and 2-cyano-1,3-butadiene ( 3 ) (Figure )would enable radioastronomical searches for these compounds. Each of these nitriles has been proposed as a likely component of the ISM. − Additionally, these nitriles are acyclic isomers of the aromatic heterocycle, pyridine, which has yet to be identified in the ISM . Detection of any of these nitriles would provide additional motivation to detect pyridine and other aromatic heterocycles.…”

Weak Interactions in Interstellar Chemistry: How Do Open Shell Molecules Interact with Closed Shell Molecules?

“…The CN radical was one of the first molecules to be detected in the ISM . However, notwithstanding the numerous dynamics and reactivity studies on CN, − not much information is available about its involvement in weak interactions. , In agreement with the conventional Lewis structure representation of the CN radical, the spin density resides on C alone (spin density = 1) and N possesses the lone pair of electrons. It, thus, presents the interesting case wherein both the C and N terminals can independently act as hydrogen bond donors and/or participate in other types of weak interactions.…”

On the formation and the isomer specific detection of methylacetylene (CH3CCH), propene (CH3CHCH2), cyclopropane (c-C3H6), vinylacetylene (CH2CHCCH), and 1,3-butadiene (CH2CHCHCH2) from interstellar methane ice analogues

“…23 Meanwhile, 1,3-butadiene's reaction with the phenyl radical generates 1,4-dihydronaphthalene (C 10 H 10 ), 41,136 the reaction with the tolyl radical forms 5-and 6-methyl-1,4-dihydronaphthalene (C 11 H 12 ), 42 and its reaction with the 1-napthyl radical synthesizes dihydrophenanthrene (C 14 H 12 ). 137 Furthermore, 1,3-butadiene can also react with the cyano radical to form pyridine (C 9 H 5 N), 3,138 and its reaction with pyridyl radicals (C 5 H 4 N) can produce 1,4-dihydro (iso)quinolone (C 9 H 9 N). 3 The other C 4 H 6 isomers detected here, 1,2-butadiene, 1-butyne, and 2-butyne, have also been shown to react with dicarbon to make RSFRs.…”