Abstract
The formation of polycyclic aromatic hydrocarbons (PAHs) is a strong global concern due to their harmful effects. To help the reduction of their emissions, a crucial understanding of their formation and a deep exploration of their growth mechanism is required. In the present work, the formation of benzo(a)pyrene was investigated computationally employing chrysene and benz(a)anthracene as starting materials. It was assumed a type of methyl addition/cyclization (MAC) was the valid growth mechanism in this case. Consequently, the reactions implied addition reactions, ring closures, hydrogen abstractions and intramolecular hydrogen shifts. These steps of the mechanism were computed to explore benzo(a)pyene formation. The corresponding energies of the chemical species were determined via hybrid density funcional theory (DFT), B3LYP/6-31+G(d,p) and M06-2X/6-311++G(d,p). Results showed that the two reaction routes had very similar trends energetically, the difference between the energy levels of the corresponding molecules was just 6.13 kJ/mol on average. The most stable structure was obtained in the benzo(a)anthracene pathway.
Highlights
Polycyclic aromatic hydrocarbons (PAHs) consist of a set of several thousands of compounds of ubiquitous pollutants in the environment
The parent PAH molecules have been regarded by researchers as being representatives for all the PAHs
Some recent studies strongly suggest further completion of the list in order to cover the wide range of polycyclic aromatic components that occur in any studied samples [5,6,7]
Summary
Polycyclic aromatic hydrocarbons (PAHs) consist of a set of several thousands of compounds of ubiquitous pollutants in the environment. They have structures composed of multiple aromatic rings creating a concern to people’s health [1,2]. The intensity of their monitoring in the environment started more than 40 years ago, with the appearance of a list issued by the U.S Environmental Protection. Agency (EPA) in 1976 [3,4]. That list contained 16 priority PAHs (often called “parent PAHs”, Figure 1). Some recent studies strongly suggest further completion of the list in order to cover the wide range of polycyclic aromatic components that occur in any studied samples [5,6,7]
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