Coding and ordering Kekulé structures

Area of Science:

• * Organic Chemistry
• * Theoretical Chemistry
• * Computational Chemistry

Background:

• * Kekulé structures are fundamental to understanding the aromaticity and electronic properties of conjugated molecules.
• * Existing methods for classifying and ordering Kekulé structures can be complex, especially for larger polycyclic systems.

Purpose of the Study:

• * To introduce and explore the concept of numerical Kekulé structures.
• * To develop a systematic method for coding and ordering geometrical Kekulé structures.
• * To investigate the applicability of numerical Kekulé structures across various classes of polycyclic conjugated systems.

Main Methods:

• * Application of numerical Kekulé structure concept to catacondensed, pericondensed, and fully arenoid benzenoid hydrocarbons, thioarenoids, and [N]phenylenes.
• * Analysis of the relationship between numerical and geometrical Kekulé structures.
• * Development of strategies for reconstructing geometrical structures from numerical codes.

Main Results:

• * Numerical Kekulé structures provide a viable coding and ordering system for geometrical Kekulé structures in diverse polycyclic conjugated systems.
• * Reconstruction of geometrical Kekulé structures from numerical codes is straightforward for catacondensed systems.
• * For pericondensed benzenoid hydrocarbons, a combination of Wiswesser codes and numerical codes is required for reconstruction, with methods to resolve ambiguities arising from multiple geometrical structures per numerical code.

Conclusions:

• * Numerical Kekulé structures offer a powerful and generalizable tool for the systematic study of conjugated molecules.
• * The proposed coding system simplifies the analysis and comparison of Kekulé structures.
• * Challenges in reconstructing structures for pericondensed systems are addressed, enhancing the utility of the numerical approach.