Estimation of Properties of Acyclic Organic Compounds through Conjugation
Constantinou, Leonidas A.
Mavrovouniotis, Micheal L.
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Systematic methods for the prediction of thermodynamic and physical properties from the molecular structure of substances are essential for the modeling, analysis, and design of chemical processes. The objective of this work is to develop a new class of computer-based methods for the estimation of properties of organic compounds from their molecular structure. The proposed approach is based on the contributions of Atoms and Bonds to the properties of Conjugate forms (ABC) of a molecular structure. Conjugate forms are alternative formal arrangements of valence electrons in a molecule; a real chemical compound can be considered the hybrid of all its conjugates. Conjugates are extensively used in organic chemistry to draw qualitative conclusions on the stability and chemical properties of a compound. Until now, however, they have been completely ignored in property estimation for chemical engineering purposes.<P>In the proposed ABC approach, we start by generating all conjugate forms of the molecule whose properties we wish to estimate. Physical and thermodynamic properties are assigned to each conjugate, simply by summing contributions from atoms and bonds in the particular electronic arrangement of the conjugate. To eliminate the number of adjustable parameters, we introduce conjugation operators, that is, recipes that yield recessive conjugates when applied to the dominant conjugate. Then, the properties of the conjugates are combined, through semi-empirical formulae, to derive the properties of the compound.<P>The method was applied to the estimation of a number of thermodynamic and physical properties of hydrocarbons and organic acyclic compounds containing oxygen, nitrogen, or sulfur. It was also employed for the approximate estimation of properties of unstable intermediates. Compared to the typical group-contribution methods, our method is more accurate in all these cases.<P>The ABC technique enables simple yet accurate estimation of physical and thermodynamic properties, and therefore improves the modeling, analysis, or design of products and processes.