Browsing by Author "Constantinou, Leonidas A."
Results Per Page
Sort Options
Item Computer-Manipulation of Conjugate Forms in Proper Estimation(1991) Mavrovouniotis, Micheal L.; Constantinou, Leonidas A.; ISRPhysical and chemical properties of pure compounds and mixtures are essential for the analysis and design of chemical processing systems. A method for the estimation of properties of organic compounds from their molecular structure is presented, based on the contributions of Atoms and Bonds in the properties of Conjugate forms of a molecular structure (ABC). A real chemical compound can be considered the hybrid of a number of conjugates, which are alternative formal arrangements of the valence electrons of the molecule. The property-estimation method generates all conjugate forms of the molecule and assigns properties to each conjugate, simply by summing contributions from atoms and bonds in the particular electronic arrangement of the conjugate. The properties of the actual compound are then derived from the properties of the conjugates. The generation and analysis of conjugates is based on symbolic computation and Object-Oriented Programming (OOP). Atoms, bonds, molecules, electron pairs, and other entities can be represented as interconnected objects within OOP. The generation, comparison, and analysis of conjugates can be carried out through computer- based manipulation of the objects and their interconnections. One needs to encode operators which generate the conjugates, as well a rules for pruning the generation so that only the most important conjugates are considered. The nature and connectivity of atoms within a molecule determine the physical and chemical properties of the molecule. Traditional group-contribution methods eliminate much of the detailed molecular-structure information at an early stage of the property-estimation effort. Through symbolic computation and the concept of conjugation, the ABC approach aims to use molecular structure information more effectively.Item Estimation of Properties of Acyclic Organic Compounds through Conjugation(1993) Constantinou, Leonidas A.; Mavrovouniotis, Micheal L.; ISRSystematic 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.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.
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.
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.