Nature Publishing Group, publisher of Nature, and other science journals and reference works
Nature
my account e-alerts subscribe register
   
Thursday 21 September 2017
Journal Home
Current Issue
AOP
Archive
Download PDF
References
Export citation
Export references
Send to a friend
More articles like this

Letters to Nature
Nature 261, 566 - 567 (17 June 1976); doi:10.1038/261566a0

Statistical interpretation of enthalpy–entropy compensation

R. R. KRUG, W. G. HUNTER & R. A. GRIEGER

Department of Chemical Engineering, University of Wisconsin, Madison, Wisconsin 53706

TYPICALLY, enthalpy and entropy estimates from kinetic and equilibrium data are highly correlated, varying in a linear fashion with one another (enthalpy–entropy compensation effect). This effect can be readily explained in most cases simply as a statistical or data handling artefact. The statistical analysis presented here reveals three novel insights. First, the enthalpy and entropy parameter estimates are highly correlated, such that estimated correlation coefficients > 0.95, say, do not imply chemical causation. Second, enthalpy and entropy estimates are distributed by experimental and measurement errors in elliptical probability regions that are very elongated and appear as lines. The slope of such lines is the harmonic mean of the experimental temperatures. Third, estimates of enthalpy and free energy at the harmonic mean of the experimental temperatures are not statistically correlated, so any observed structured variation between these parameter estimates arises from the chemical effect alone. Note that, since the thermodynamic potentials are interrelated by the Maxwell relationships, a correlation between any two potentials can be transformed to give the corresponding correlation between any other two. We now discuss these results to resolve a number of issues concerning a much disputed data set.

------------------

References

1. Leffler, J. E., and Grunwald, E., Rates and Equilibria of Organic Reactions, 315–402 (Wiley, New York, 1963).
2. Leffler, J. E., J. org. Chem., 20, 1202–1231 (1955).
3. Craft, M. J., and Lester, C. T., J. Am. chem. Soc., 73, 1127–1128 (1951).
4. Leffler, J. E., Nature, 205, 1101–1102 (1965).
5. Exner, O., Coll. Czech. chem. commun., 29, 1094–1113 (1964).
6. Exner, O., Nature, 201, 488–490 (1964).
7. Hammett, L. P., Physical Organic Chemistry, 391–408 (McGraw-Hill, New York, 1970).
8. Lumry, R., and Rajender, J., Biopolymers, 9, 1125–1227 (1970); J. phys. Chem., 75, 1387–1401 (1971).
9. Exner, O., Coll. Czech. Chem. Commun., 37, 1425–1444 (1972).
10. Exner, O., Nature, 227, 366–367 (1970).
11. Blackadder, D. A., and Hinshelwood, C., J. chem. Soc., 2720–2727 (1958).
12. Leffler, J. E., J. org. Chem., 31, 533–537 (1966).
13. Brown, R. F., J. org. Chem., 27, 3015–3026 (1962).



© 1976 Nature Publishing Group
Privacy Policy