Stein and Brown

Finer distinction with respect to structural environment 

Combination of heteroatoms into larger functional units 

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Figure 9J.2 Estimation of Tb (1 atm) for pentachlorobenzene using the method of Stein and Brown [39].

The group contribution method Stein and Brown (1994) developed is the most robust group contribution method that can be applied in a straightforward manner i.e., it can cover a broader variety of chemicals than the Simamora and Yalkowsky and Cramer methods (described above) and is relatively easy to use compared to the method of Lai et al. (1987) (described below). The work is an extension of the work by Jobak and Reid (1987). The extension is primarily an increase in the number of fragment constants, from 41 to 85. However, many of the new groups are simply subdivisions of those Jobak and Reid used. The method assumes no interaction between fragments. A computerized version of the estimation method, called MPBPVP, is available from Syracuse Research Corporation (Syracuse, NY). 

For the 4,426-compound data set used to develop this method, the predicted boiling points had an average absolute error of 15.5 K (3.2%). Stein and Brown (1994) also evaluated their method on an independent test set of 6,584 compounds and found the predicted boiling points had an average absolute error of 20.4 K (4.3%). 

The method used by the MPBPVP program available from SRC has been adapted from the Stein and Brown method (1994). This is a group contribution method, which has an average error of 4.3%. 

VP estimation is performed by the MPBPWIN program using three separate methods (1) the Antoine method, (2) the modified Grain method, and (3) the Mackay method. All three use the normal boiling point to estimate VP. Unless the user enters a boiling point on the data-entry screen, MPBPWIN uses the estimated boiling point from the adapted Stein and Brown method. When a boiling point is entered on the data entry screen, MPBPWIN uses it. Each VP method is discussed below. 

One of the most important contributions to this field was provided by Stein and Brown [117], who extended Joback and Reid s group contribution method [122], The authors calculated 85 group contributions and used a nonlinear quadratic equation to correctly predict BP at high temperatures. The authors calculated MAE = 15.5 K for a set of 4426 compounds and predicted another independent set of 6584 compounds with MAE = 20.4 K. The method was further parameterized by Syracuse Research Inc using 6484 compounds and was used in the MPBPVP program [101]. 

The Joback method was modified in the MPBPVP program to include the same 85 groups used by the Stein and Brown [117] method for BP calculation. The MPBPVP program has a calculated MAE = 44 K for a set of 2045 compounds. 

Besides the shape, another important factor that affects the electronic properties and chemical reactivity of PAHs is the nature of the periphery. According to Clar s classification, the graphitic molecules with armchair and cove peripheries shown in Fig. 3.14 (A and B) are all-benzenoid PAHs. In addition to these linear topologies, Stein and Brown considered two other peripheral structures, i.e. acene-like (C) and quinoidaT (D) structures, which lie in a higher energy state and thus show higher chemical reactivity [62]. 

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