G wynedd L L57 2U WEliminative fission of cyclobutanes has been compared with that of analogous cyclopropanes; reactivity differences of 103.7-104*8 have been determined. In both sets of compounds, mechanisms have been shown t o involve rate-determining ring fission. The possibilities that the large reactivity differences between the comparably strained systems are due either t o peculiarity in the cyclobutane structures or to their abnormally slow deprotonation are rejected. Analysis of strain in the t w o systems suggests that as ring fission occurs, dispersal of the excess of enthalpy of the cyclobutanes is a less sensitive function of extension of a bond in the ring than for the cyclopropanes. The behaviour of these systems is compared with cleavage of cyclopropanes and cyclobutanes in other reactions; the results are remarkably similar. Calculations using the MIND03 programme have been carried out for eliminative fissions of 1274 J. CHEM. SOC. PERKIN TRANS.

Cyclobutanes, by comparison with cyclopropanes, are reluctant to undergo eliminative ring fission; the very similar strain energies are released differently in the transition states for fission.

Activation parameters for the fission of cyclopropanols and cyclobutanols with phenyl groups a or phenylthio or phenylsulphonyl groups j3 to the hydroxy group have been obtained. The results show very large differences in reactivity between cyclopropanols and cyclobutanols; such differences are also found in energy profiles for the opening of cycloalkoxide ions obtained by using MIND03. The results are entirely compatible with other three-membered/four-membered ring comparisons and the role of strain in these systems is discussed. Attempts to extend the well established enforced catalysis of cycloalkanol ring fission to electrophiles other than Brsnsted acids have failed.

The compound referred to in the last line of the text should be (8). Footnote e in Table 1 should state 'the value given in reference 2 for an ionic strength of 1.0 M is 2.4 x 10-3 M-1 s-1.'Electronically typeset and printed by Heffers Printers Ltd,

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Rates of eliminative ring fission of cyclopropanols under basic conditions are 105 to lo9 faster than those of the related cyclobutanols; neither excess enthalpies of the systems nor classical ideas on strain distribution in small rings account for these ratios.

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Die Ringspaltungsgeschwindigkeiten von (I) und (II) werden 13C‐ und 1H‐NMR‐spektroskopisch untersucht und miteinander verglichen.