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Variable connectivity index for cycle-containing structures
1National Institute of Chemistry, 1001 Ljubljana, POB 3430, The Republic of Slovenia.
Journal of Chemical Information and Computer Sciences
|June 21, 2001
Summary
Researchers investigated the heuristic adjustment of connectivity indices for cyclic structures. They found that carbon atoms within rings and those in exocyclic bonds contribute differently to molecular additivity, impacting boiling point predictions.
Area of Science:
- Chemistry
- Computational Chemistry
- Molecular Modeling
Background:
- Connectivity indices are used in quantitative structure-property relationships (QSPR).
- An empirical adjustment of -1/2 was historically applied to connectivity indices for cyclic structures.
- The origin and justification for this adjustment were not fully understood.
Purpose of the Study:
- To investigate the origin of the heuristic -1/2 adjustment for connectivity indices in cyclic compounds.
- To differentiate the contributions of cyclic and exocyclic carbon atoms to molecular properties.
Main Methods:
- Analysis of molecular graphs and vertex valency.
- Examination of carbon atom roles in ring structures versus exocyclic bonds.
- Correlation analysis with boiling points of cycloalkanes and alkylcycloalkanes.
Main Results:
- The study provides insight into the origin of the empirical -1/2 correction for cyclic structures.
- Contributions of "cyclic" and "acyclic" carbon atoms to molecular additivity were found to differ.
- This difference was observed in the boiling points of cycloalkanes and alkylcycloalkanes.
Conclusions:
- The heuristic adjustment in connectivity indices for cyclic structures is supported by differing contributions of cyclic and acyclic atoms.
- Understanding these atomic contributions enhances the accuracy of molecular property predictions.
- This research clarifies a long-standing empirical modification in molecular graph theory.