Structure-boiling point relationships

D. PlavSid, N. Trinajstid, D. Amid, and M. Soskid, Comparison between the structure-boiling point relationships with different descriptors for condensed benzenoids. New J. Chem. 22 (1998) 1075-1078. 

Hosoya et al. discussed the topological rules which apply to structure - boiling points relationships. However, the best correlation is not a topological, but an empirical one ... 

When the property being described is a physical property, such as the boiling point, this is referred to as a quantitative structure-property relationship (QSPR). When the property being described is a type of biological activity, such as drug activity, this is referred to as a quantitative structure-activity relationship (QSAR). Our discussion will first address QSPR. All the points covered in the QSPR section are also applicable to QSAR, which is discussed next. 

Another way of predicting liquid properties is using QSPR, as discussed in Chapter 30. QSPR can be used to And a mathematical relationship between the structure of the individual molecules and the behavior of the bulk liquid. This is an empirical technique, which limits the conceptual understanding obtainable. However, it is capable of predicting some properties that are very hard to model otherwise. For example, QSPR has been very successful at predicting the boiling points of liquids. 

Deardon, J.C. (2003) Quantitative Structure-Property Relationships for Prediction of Boiling Point, Vapor Pressure and Melting Point. Environmental Toxicology and Chemistry, 22(8), 1696-1709. 

In many cases of practical interest, no theoretically based mathematical equations exist for the relationships between x and y we sometimes know but often only assume that relationships exist. Examples are for instance modeling of the boiling point or the toxicity of chemical compounds by variables derived from the chemical structure (molecular descriptors). Investigation of quantitative structure-property or structure-activity relationships (QSPR/QSAR) by this approach requires multivariate calibration methods. For such purely empirical models—often with many variables—the... 

It is important to consider the molecular interactions in liquids that are responsible for their physicochemical properties (such as boiling point, melting point, heat of vaporization, surface tension, etc.), which enables one to both describe and relate the different properties of matter in a more clear manner (both qualitatively and quantitatively). These ideas form the basis for quantitative structure activity relationship (QSAR Birdi, 2002). This approach toward analysis and application is becoming more common due to the enormous help available from computers. 

Most of the structure-A//v relationships have been developed for either AHv at 25°C or for the normal boiling point enthalpy, AHvb. Relationships of both types are discussed below. 

Dearden, J.C., Quantitative structure-property relationships for prediction of boiling point, vapor pressure and melting point, Environ. Toxicol. Chem., 22, 1696-1709, 2003. 

Generic chemical class data are often relevant to assessing potential toxicity and should be a part of any evaluation. The relevant information includes structure-activity relationships and physical-chemical properties, such as melting point, boiling point, solubility, and octanol-water partition coefficient. Physical-chemical properties affect an agent s absorption, tissue distribution, biotransformation, and degradation in the body. 

Normal Boiling Points of Organic Compounds Correlation and Prediction by a Quantitative Structure—Property Relationship. 

The aforementioned macroscopic physical constants of solvents have usually been determined experimentally. However, various attempts have been made to calculate bulk properties of Hquids from pure theory. By means of quantum chemical methods, it is possible to calculate some thermodynamic properties e.g. molar heat capacities and viscosities) of simple molecular Hquids without specific solvent/solvent interactions [207]. A quantitative structure-property relationship treatment of normal boiling points, using the so-called CODESS A technique i.e. comprehensive descriptors for structural and statistical analysis), leads to a four-parameter equation with physically significant molecular descriptors, allowing rather accurate predictions of the normal boiling points of structurally diverse organic liquids [208]. Based solely on the molecular structure of solvent molecules, a non-empirical solvent polarity index, called the first-order valence molecular connectivity index, has been proposed [137]. These purely calculated solvent polarity parameters correlate fairly well with some corresponding physical properties of the solvents [137]. 

The relationship between a chemical s structure and its biological action has been studied extensively for over a century (16). In cases where there is not a complete understanding of the mechanism/mode of action or where the influence of functional groups is not known or obvious, there is a vast body of knowledge on how different structural features within a class of chemicals may correlate with various levels of hazard. Structure-activity relations (SAR) or their mathematical treatment. Quantitative SAR (QSAR) have been developed for myriad endpoints including cancer, developmental and reproductive effects, aquatic toxicity, boiling points, water solubility and many others hazard endpoints. An instructor therefore has many opportunities to incorporate the concept of SAR at several points in the curriculum. 

Katritzky, A.R., Lobanov, V.S. and Karelson, M. (1998d). Normal Boiling Points for Organic Compounds Correlation and Prediction by a Quantitative Structure-Property Relationship. J.Chem.lnf.Comput.Sci., 38,28-41. 

Randic, M. (1996c). Quantitative Structure-Property Relationship - Boiling Points of Planar Benzenoids. New J.Chem.,20,1001-1009. 

Tetteh, J., Suzuki, T, Metcalfe, E. and Howells, S. (1999). Quantitative Structure-Property Relationships for the Estimation of Boiling Point and Flash Point Using a Radial Basis Function Neural Network. J.Chem.InfiComput.ScL, 39,491-507. 

The close relationships in the structural features of homo- and heterometallic alkoxides can be exemplified by those of Al Al(0-i-Pr)4 3 (150) and Ln Al(0-/-Pr)4 3 (18). The molecular weights of the latter in benzene correspond to their empirical formulas. All of these compounds can be distilled in the range of 200-180°C/0.1 mm, with a lowering of the boiling point as was expected from increasing the covalent character which results from lanthanide contraction in the series. The tetrameric aluminum isopropoxide A1 A1(0-/-Pr)4 3 or A1(0-/-Pr)3 4, however, disproportionates and distills as a dimeric vapor around... 

Katritzky AR, Lobanov VS, Karelson M. Normal boiling points for organic compounds Correlation and prediction by a quantitative structure-property relationship. J Chem Inf Comput Sci 1998 38 28-41. 

The relationship between the molecular structure of an aroma compound and its threshold is still unclear. Volatility of a compound may not relate to its threshold. For example, the threshold of ethanol (boiling point is 78°C) is much higher than octanol (boiling point is 195°C) or other homologous alcohol. Ethanol has high volatility but low odor intensity. It is often used as a solvent in compounded flavors. 

Amboni, D., de, M.C., da Silva Junkes, B., Yunes, R.A. and Heinzen, V.E.F. (2002b) Quantitative structure-property relationship study of chromatographic retention indices and normal boiling point for oxo compounds using the semi-empirical topological method. J. Mol. Struct. (Theochem), 586, 71-80. 

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