Melander

Melander first sought for a kinetic isotope effect in aromatic nitration he nitrated tritiobenzene, and several other compounds, in mixed acid and found the tritium to be replaced at the same rate as protium (table 6.1). Whilst the result shows only that the hydrogen is not appreciably loosened in the transition state of the rate-determining step, it is most easily understood in terms of the S 2 mechanism with... 

Melander, L. (a) (i960). Isotope Effects on Reaction Rates. New York Ronald Press. (6) (1950). Ark. Kemi 2, 211. 

For mote complete discussion of isotope effects, see W H. Saunders, in Investigation cf Rates and Mechanisms of Reactions, E. S. Lewis, ed.. Techniques of Chemistry, 3rd ed., 4)1. VI, Part 1, John Wiley Sons, New York, 1974, pp. 211-255 L. Melander and W. H. Saunders, Jr., Reaction Rates of Isotopic Molecules, John Wiley Sons, New bik, 1980 W. H. Saunders, in Investigation of Rates and Mechanisms of Reactions, C. F. Bemasconi, ed.. Techniques of Chemistry, 4th ed., Vol. VI, Part 1, John Wiley Sons, New feik, 1986, Chapter VUI. 

L. Melander, Isotope Effects on Reaction Rates, Ronald Press, New %ik, 1960. 

L. Melander and W. H. Saunders, Reaction Rates of Isotopic Molecules, Wiley, New York, 1980, 331 pp. 

The reason for this difference in selectivity of different electrophilic reagents between the 2- and 3-positions must be sought in the finer details of the mechanism of electrophilic aromatic substitution Melander and co-workers are studying this problem by means of isotope effects. 

C. FJorvath, W. Melander and I. Molnar, Solvophobic interactions in liquid chromatography with non-polar stationaiy phases , 7. Chromatogr. 125 129 (1976). 

Cs Horvath and W. R. Melander, Theory of chromatography , in Chromatography Fundamentals and Applications of Chromatographic and Electrophoresis Methods. Part A Fundamentals and Techniques, Helftmann E. (Ed.), Journal of Cliromatography Library, Vol. 22, Ch. 3, A28-A135 (1983). 

L. Melander, Isotope Effects on Reaction Rates, The Ronald Press Co., New York, 1959. J. Bigeleisen, Pure Appl. Chem., 8 (1964) 217. 

In the following, a detailed exposition of Bartell s (1961a) theory of steric isotope effects will be given (Section II, A), and an alternative model will be developed, based on somewhat different assumptions about the timing in the transition state, which leads to predictions at variance with the experimental results (Section II, B). In both of these sub-sections, special reference will be made to the work of Melander and Carter (1964). Finally, a selective non-comprehensive review of other experimental work in this field will be presented (Section III). 

The work of Melander and Carter (1964) on 2,2 -dibromo-4,4 -di-carboxybiphenyl-6,6 -d2 (1) has been referred to above in the introductory and theoretical sections, where it was pointed out that the availability of two detailed theoretical computations of the inversion barrier (Westheimer and Mayer, 1946, Westheimer, 1947 Hewlett, 1960) made this system especially attractive for the study of steric isotope efifects. Furthermore, in the preferred initial-state conformation the two bromines are probably in van der Waals contact (cf. Hampsoii and Weissberger, 1936 Bastiansen, 1950), and thus initial-state steric effects are unaffected by deuterium substitution in the 6 and 6 positions. The barrier calculations provided two different theoretical values for the non-bonded H Br distance in the transition state which, together with the corresponding H Br potential function, could be inserted in equation (10) to yield values for A AH. For... 

L. Melander, Department of Organic Chemistry, University of Goteborg and Chalmers Institute of Technology, S-402 20 Goteborg 5, Sweden. 

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