Abstract
BackgroundChrysanthemic acid (CHA) is a major product from the photodecomposition of pyrethrin which is an important class of pesticide compounds.In the following paper, Hybrid density functional theory (DFT) calculations of the potential energy surface (PES) for three possible channels decomposition of chrysanthemic acid (cis-trans isomerization, rearrangement and fragmentation) have been carried at the B3LYP/6-311+G** level of theory. DFT was employed to optimize the geometry parameters of the reactants, transition states, intermediates and products based on detailed potential energy surfaces (PES).ResultsOur results suggest that all three pathways of CHA are endothermic. DFT calculations revealed that the activation barriers for cis-trans isomerization are low, leading to a thermodynamically favorable process than other two pathways. We also investigated the solvent effect on the PES using the polarizable continuum model (PCM). In addition, time-dependent density functional theory (TDDFT) calculations showed that these reactions occur in the ground state rather than in an excited state.ConclusionThe rearrangement process seems to be more favorable than the decomposition of CHA to carbene formation. The solvent effect calculations indicated no changes in the shape of the PES with three continua (water, ethanol and cyclohexane), although the solvents tend to stabilize all of the species.
Highlights
Chrysanthemic acid (CHA) is a major product from the photodecomposition of pyrethrin which is an important class of pesticide compounds
Three pathways are possible for the decomposition reaction of chrysanthemic acid, as described in an introduction and as displayed in Chart 1: trans-cis isomerization (P1-P3), fragmentation, cleavage of the 1, 3 and 1, 2 bonds (P1-P5) and rearrangement (P2-P4)
This project was designed to explore the potential energy surface (PES) for the photodecomposition of chrysanthemum acid, which is a major product from the decomposition of pyrethrine pesticides
Summary
Chrysanthemic acid (CHA) is a major product from the photodecomposition of pyrethrin which is an important class of pesticide compounds. Hybrid density functional theory (DFT) calculations of the potential energy surface (PES) for three possible channels decomposition of chrysanthemic acid (cis-trans isomerization, rearrangement and fragmentation) have been carried at the B3LYP/6-311+G** level of theory. Experimental studies have been reported that pyrethrins degrade rapidly when exposed to sunlight [3]. Chrysanthemic acid [2, 2-dimethyl-3-(2methyl-1-propenyl)] is one of the products from pyrethrin photodecomposition and is widely used as the acidic part of synthetic pyrethroidin insecticides [4,5,6,7,8,9]. The photochemical degradation of the acid components of pyrethrins has been examined in numerous studies. Sasaki et al [10] and Ueda and Matsui [11] found that carbons 1 and 2 (Scheme 1) of the main cyclopropane group are cleaved, subsequently leading to the formation
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