Formyl Cyanide With The Theory Of The Reaction Mechanism

Ramification of carboxyl has important status in orgnic chemistry. It could be found not only in atmosphere but also in the interstellar medium. Formyl cyanide (HCOCN), a species with considerable organic synthetic interest, has a variety of potential uses as a formylating agent for nucleophilic species. HCOCN has also attracted much spectroscopic interest since it is light enough to yield rotationally resolvable rotational, vibrational, and electronic spectra [1]. Moreover, HCOCN, which contains the nitrile and carbonyl functional groups and prevalent exists in the interstellar medium, is a molecule of potential astrophysical interest [2]. Recently, some considerable interest has been given to the prototype of the acyl cyanide family of compounds. Despite its simplicity, formyl cyanide has been successfully synthesized twenty years ago, The elusive formyl cyanide molecule was finally identified in 1986 by Judge et al [3]. Also in 1986, Goddard [4] reported the first ab initio results on the structure, vibrational frequencies, and dipole moment of formyl cyanide. Following this, an independent spectroscopic observation of the pyrolysis products of CH3OCH2CN was reported by Clouthier and Moule [5]. In that study, it was concluded that formyl cyanide accounted for no more than about 10% of the total pressure in the cell. The millimeter-wave spectrum of formyl cyanide was reported by Bogey et al [6] in 1988. In 1990, a more extensive characterization was reported by Vallée et al. [7] They observed the photoelectron, IR, and UV spectra of formyl cyanide formed by the retro-ene thermolysis of CH2=CHCH2OCH2CN at 1270K (997°C). Recently the AA" - XA' electronic transition of formyl cyanide has been revisited and studied at high resolution by Karolczak et al. [8] Besides the earlier paper of Goddard [4], Csaszar [9] recently reported a new theoretical prediction of the vibrational and rotational spectra of formyl cyanide and thioformyl cyanide. Wyn Lewis-Bevan et al [10] reported that formyl cyanide was a stable molecule with half-life of 45.5h; they also suggested that it readily reacts with water to form HCOOH and HCN. Several theoretical works were devoted to the unimolecular reactions [11-13] and enthalpy of formation [14, 15] of HCOCN in the ground state. It was found that HCOCN is rather stable at room temperature, which is in agreement with experimental findings.Despite the effort taken, the reaction with radical existed in the atmosphere has not been experimentally and theoretically studied so far, because more active F radical may exist in the atmosphere during the process of chlorofluorocarbons decomposition. In this paper, we studied the reaction mechanism of fluorin radical with formyl cyanide.All calculations were performed with the Gaussian 98 program package. [16] Geometries were initially optimized at the UB3LYP/6-311G** level. Harmonic vibrational frequencies were calculated to check whether the obtained species is a minimum isomer (with all real frequencies) or a transition state (with one and only one imaginary frequency). For each transition state, the intrinsic reaction coordinate (IRC) calculations were performed to guarantee its correct connection to the designated isomers. Finally, to obtain more reliable energetics, the CCSD/6-311G** were carried out.This article studies the reaction mechanism of radicals with formyl cyanide to perfect the systerm of the radicals with formyl cyanide.1. Theoretical study on the reaction mechanism of fluorine radical with formyl cyanide:A detailed computational study is performed on the radical-molecule reaction between the fluorine radical (F) and formylcyanide (HCOCN). At the CCSD//UB3LYP/6-311G** level, the barrier of H-abstraction to provide (HF+COCN) is 15.6 kJ/mol. The barrier of the addition to form HCOCFN is 35.3 kJ/mol. However, there is no barrier of the FCHOCN's formation. Subsequently, there are two highly competitive dissociation pathways for FCHOCN: One is the formation of the direct H-extrusion product H+FCOCN, and the other is the formation of H+FCOCN via the intermediate FCOHCN. Because of the influence of the strong electron acceptor-CN to the acyl, The addition-elimination is more competitive than the direct H-transfer, in contrast to previous expectation. The present results can be useful for future experimental investigation on the title reaction.The symmetries of HOMO of fluorine radical and the LUMO of formyl cynaide that distributes in formyl are matching to overlap. Moreover, the energy of fluorine radical's HOMO(-0.46eV)is close to the formyl cynaide's LUMO(-0.11eV). The process is obtained directly without energy barrier. So the addition-elimination process is more competitive than direct H-abstraction.2. Theoretical study on the reaction mechanism of vinyl radical with formyl cyanide:A detailed computational study is performed on the radical-molecule reaction between the vinyl radical (C2H3) and formylcyanide (HCOCN). At the UB3LYP/6-311G** level, the barrier of the addition to form L1(H2CCHCOHCN) is 9.1kJ/mol. The barrier of H-abstraction to provide P2(CH2=CH2+COCN)is 19.2kJ/mol. The barrier of the addition to form L8(H2CCHOCHCN) is 25.0kJ/mol. The barrier of H-abstraction to provide P7(HCCH+HOCHCN) is 93.3kJ/mol Subsequently, there is the most competitive dissociation pathway for L1( H2CCHCOHCN ) : It is the formation of the H-transfer product L3(H2CCH2COCN), subsequently the formation of P2 is obtained via the C-C rupture. Because of the influence of the strong electron acceptor-CN to the acyl, The addition-elimination is more competitive than the direct H-transfer, in contrast to previous expectation. The present results can be useful for future experimental investigation on the title reaction.The symmetries of HOMO of vinyl radical and the LUMO of formyl cyanide, which distributes in vinyl and formyl respectively, are matching to overlap. Moreover, the energy of vinyl radical's HOMO(-0.24eV)is close to the formyl cynaide's LUMO(-0.11eV). The process is obtained directly with lower energy barrier. The electron can easily transfer from the HOMO of vinyl radical to the LUMO of formyl cyanide. So the addition-elimination process is more competitive than direct H-abstraction.3. Theoretical study on the reaction mechanism of methyl radical with formyl cyanide:A detailed computational study is performed on the radical-molecule reaction between the methyl radical (CH3) and formylcyanide (HCOCN). At the UB3LYP/6-311G** level, The barrier of the addition to form L1(CH3COHCN)is 8.7kJ/mol. The barrier of the addition to form L2(HCOCH3CN)is 19.5kJ/mol. The barrier of the addition to provide L3(HCOCNCH3)is 21.6kJ/mol. The barrier of H-abstraction to provide P2(CH4+COCN)is 22.3kJ/mol. The barrier of the addition to provide L4 is 126.1kJ/mol. Although the barrier of Path Râ†'L1 which belongs to the addition-elimination mechanism is the lowest. The influence of the strong electron acceptor-CN to oxygen radical, the barrier of L1's dissociation is higher than TSR/L1. So the addition-elimination is less competitive than the direct H-transfer, in contrast to previous expectation.