Bond contribution method

The value of the torsional energy increment has been variously estimated, but TORS = 0.42 kcal mol was settled on for the bond contribution method in MM3, In the full statistical method (see below), low-frequency torsional motion should be calculated along with all the others so the empirical TORS inererneut should be zero. In fact, TORS is not zero (Allinger, 1996). It appears that the TORS inererneut is a repository for an energy eiror or errors in the method that are as yet unknown. 

Group contribution and bond contribution methods (Hine and Mookerjee 1975, Meylan and Howard 1991) ... 

Meylan, W. M., Howard, P. H. (1991) Bond contribution method for estimating Henry s law constants. Environ. Toxicol. Chem. 10, 1283-1293. 

A more recent study for estimating Henry s law constants using the bond contribution method was provided by Meylan and Howard (1991). In this study, the authors updated and revised the method developed by Hine and Mookeijee (1975) based on new experimental data that have become available since 1975. Bond contribution values were determined for 59 chemical bonds based on known Henry s law constants for 345 organic compounds. A good statistical fit [correlation coefficient (r ) = 0.94] was obtained when the bond contribution values were regressed against known Henry s law constants for all compounds. For selected chemicals classes, r increased slightly to 0.97. 

Meylan WM, Howard PH. 1991. Bond contribution methods for estimating Henry s Law Constants. Environ Toxicol Chem 10 1283-1293. 

Illustrative Example 6.4 Estimating Air-Water Partition Constants by the Bond Contribution Method... 

Illustrative Example 6.4 Estimating Air-Water Partition Constants by the Bond Contribution Method Problem Estimate the Kiavi values at 25°C of (a) n-hexane, (b) benzene, (c) diethylether, and (d) ethanol using the bond contribution values given in Table 6.4. Compare these values with the experimental air-water partition constants given in Table 3.4. Note that for a linear or branched alkane (i.e., hexane) a correction factor of +0.75 log units has to be added (Meylan and Howard, 1991). 

Method of Meylan and Howard Meylan and Howard [9] expanded the bond contribution method of Hine and Mookerjee. Based on 345 compounds they derived bond contributions for 59 different bond types. Their method has been validated with an independent set of 74 structurally diverse compounds, obtaining a correlation coefficient of 0.96. Their method also needs correction factors for several structural-substructural features. This method has been implemented into a Henry s law constant program performing AWPC (25°C) estimations from SMILES input [15]. 

Method 2 Bond Contribution Method of Meylan and Howard (1991)... 

More recently, Brennan et al. (1997) compared five methods for estimating KAW, namely the vapor pressure/solubility ratio, the group or bond contribution method, linear solvation energy methods, and molecular connectivity. The authors compared the methods by application to a common set of 150 chemicals and concluded that the Meylan and Howard (1991) bond contribution method and the molecular connectivity index method of Nirma-lakhandan and Speece (1988) are comparably accurate, having standard deviations of, 0.29 and 0.34 log units, respectively. 

This method is thus about equivalent in accuracy to the bond contribution method, but the connectivity index does contain information about molecular configuration or topology which is absent from the simple bond contribution method. It thus is inherently more likely to express differences between isomers. Its primary disadvantage is the need to deduce the indices, which can be difficult to the uninitiated. The indices lack physical meaning, which is worrisome to those who seek to understand fully the inherent nature and principles of the estimation method. 

Chemical Class Bond Contribution Method Nirmalakhandan and Speece Method... 

A natural extension of the bond energy approach is to account for interactions close to the chemical bond in question (which certainly affect the stability, and hence the thermodynamic properties). Based on this concept, a number of group contribution methods have been developed over the years, and many of these methods have been reviewed in Ref. 171. Benson s second-order group contribution method, probably the most successful and widely embraced method, was developed some 30 years ago as an improvement to bond energy (or bond contribution) methods for the prediction of thermochemical properties.167 This improvement was accomplished by accounting for ... 

WERL Treatability Database, Ryan et al. 1988) (20°C, calculated-P/C, Suntio et al. 1988) (calculated-P/C, Jury et al. 1990) (calculated-bond contribution method LWAPC, Meylan Howard 1991) (Montgomery 1993) (wetted wall column-GC, Altschuh et al. 1999) (LDV literature-derived value, FAV final adjusted value, Shen Wania 2005)... 

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