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Do Alkoxycarbonyl Substituents Stabilize Small Cycloalkane Rings?
Author(s) -
Verevkin Sergey P.,
Kümmerlin Martin,
Beckhaus HansDieter,
Galli Carlo,
Rüchardt Christoph
Publication year - 1998
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/(sici)1099-0690(199804)1998:4<579::aid-ejoc579>3.0.co;2-#
Subject(s) - cycloalkane , chemistry , organic chemistry , stereochemistry , combinatorial chemistry , medicinal chemistry , catalysis
The standard enthalpies of formation Δ H f °(g) of mono‐ and gem ‐di(alkoxycarbonyl)‐substituted cyclopropanes 1 , cyclobutanes 2 and cyclopentanes 3 have been calculated from the standard enthalpies of combustion Δ H c °, which were measured calorimetrically, in combination with the standard enthalpies of vaporization Δ H vap °. The latter were obtained for 1a − c , 2b − c and 3b − c from the temperature dependence of the vapor pressures, which were measured in a flow system. Contrary to suggestions in the literature, only weak stabilization (≤ 8 kJ · mol −1 ) of small rings by gem ‐alkoxycarbonyl substituents was observed. In this context, we give a revised value for the enthalpy of combustion of methyl cyclobutanecarboxylate. It is concluded that the known high rates of ring closure to gem ‐dialkoxycarbonyl cyclopropanes are not attributable to a ‘stabilizing effect’ resulting from conjugation between the alkoxycarbonyl substituents and the cyclopropane ring, as has been suggested in the literature. The operation of a Thorpe‐Ingold‐ or gem ‐dimethyl‐type effect would seem to offer a more satisfactory interpretation.