ACD/Boiling Point

Boiling Point

Boiling Point at 760 mmHg

The boiling point calculated by ACD/Boiling Point, in general, compares very well to the value at standard sea-level pressure:

where N is the number of structures, R is the correlation coefficient, and SD is the standard deviation.

Total number of structures in the database is over 10,000.

Correlations between the experimental and calculated boiling point values for different methods

The following is a comparison of three different approaches to the prediction of the boiling point: the ACD/Labs' Vaporization Calculator algorithm, Joback's approach, and the Egolf et al method.

The comparison was made using the paper of Egolf et al. [1] and the ACD/Boiling Point program.

In this paper, 298 chemical compounds were given for which the boiling point was predicted using two different methods: the commonly used Joback approach; and the method proposed by Egolf et al.:

where X_ij are different physicochemical descriptors, b₀ and b_i are regression coefficients.

All of these compounds had boiling points predicted with ACD/Boiling Point algorithm and a comparison of results obtained by a different method with experimental values was made.

The correlation of experimental vs. predicted values by all three methods was made according to the equation:

The results of these correlations are given in Table 1.

Table 1. Correlations between the experimental and calculated boiling point values by equation (2) for different methods.

Comparison of the standard deviations of different methods shows that ACD/Boiling Point gives the results with a discrepancy three times smaller than the Joback approach and two times better than methods of authors of Ref. [1].

Difficult cases

In Table 2 we list "pathological" cases, i.e., those cases for which the predicted boiling point has a difference of more than 20°C between at least one predicted value and the experimental result. Note that in this table there are two different columns: from the ACD/Boiling Point Program and the ACD/Boiling Point Algorithm. The difference exists when the value can be found in the database and there is a significant difference (more than 5°C) between experimental and calculated values. The statistics given in Table 1 are for data from the column ACD/Boiling Point Algorithm.

Table 2. Comparison of difficult cases.

* The difference between predicted and experimental values is more than 20°C in calculations by the method from Ref. [1] (if there is no asterisk (*) after the number, then the difference of more than 20°C occurs only in calculations using the Joback method.)

** The difference between predicted and experimental values of more than 20°C is given by both methods: Joback and the method from Ref. [1].

1. The numbering is given in accordance with Ref. [1].
2. The experimental values are taken from Ref. [1].
3. ACD/Boiling Point program.
4. ACD/Boiling Point algorithm.
5. The values are calculated by the method proposed in [1].
6. The values are calculated by the Joback approach.
7. The boiling point is given for the tautomeric form: 1,4-dihydroxybenzene.

References:
1. L.M.Egolf, M.D.Wessel and P.S.Jurs, J.Chem.Inf.Comput.Sci. 1994, 34, 947-956.

Vapor Pressure

Vapor Pressure comparison with Experiment is available in PDF format. Download the latest version of the Adobe Acrobat Reader to view or print it.

References:
1. CRC Handbook of Chemistry and Physics; Lide, D. L., Ed.; CRC Press, 73-rd Edition, 1992-1993.