Benzenoids are a subfamily of hydrocarbons (molecules that are only made of hydrogen and carbon atoms) whose carbon atoms form hexagons. These molecules are widely studied in theoretical chemistry. Then, there is a lot of problems relative to this subject, like the benzenoid generation or the enumeration of all its Kekulé structures (i.e. all valid configurations of double bonds). In this context, the computation of the local aromaticity of a given benzenoid is an important problematic since the aromaticity cannot be measured. Nowadays, computing aromaticity requires quantum chemistry calculations that are too expensive to be used on medium to large-sized molecules. But, there exist some methods related to graph theory which can allow us to compute it. In this article, we describe how constraint programming can be useful in order to compute the aromaticity of benzenoids. Moreover we show that our method is much faster than the reference one, namely NICS.

Benzenoids are a subfamily of hydrocarbons (molecules that are only made of hydrogen and carbon atoms) whose carbon atoms form hexagons. These molecules are widely studied in theoretical chemistry and have a lot of concrete applications. Therefore, generating benzenoids which have certain structural properties (e.g. having a given number of hexagons or having a particular structure from a graph viewpoint) is an interesting and important problem. It constitutes a preliminary step for studying their chemical properties. In this paper, we show that modeling this problem in Choco Solver and just letting its search engine generate the solutions is a fast enough and very flexible approach. It can allow to generate many different kinds of benzenoids with predefined structural properties by posting new constraints, saving the efforts of developing bespoke algorithmic methods for each kind of benzenoids.

The BenzAI program can automatically generate benzenoids with defined structural constraints, like the number of hexagons, the number of carbon and/or hydrogen atoms, the existence of symmetries, the number of Kekulé structures, their diameter, or more elaborate criteria like their irregularity. BenzAI allows both automatic generation and manual building of benzenoids including or excluding defined patterns. For all benzenoids with less than 10 rings, it can extract IR spectra from a database that we generated. It computes local aromaticity for closed-shell and monoradical species using circuit-based algorithms. We present practical examples of what can be done with BenzAI for a diversity of cases.

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