No abstract

No abstract

The acetolysis rates of a number of alkyl-and polymethyl-substituted cyclopropyl tosylates, bromides, and chlorides have been determined. The kinetic results in all cases are consistent with stereospecific disrotatory ring opening concerted with ionization. For trans-i3-alkyl substitution the observed rates show a regular but rather modest increase in the order CH3 < C2H= < i-C3Hv < tert-C4H9, attributed to inductive effects. The corresponding cis isomers show little variation; we attribute this to a combination of opposing steric and inductive effects. A comparison of -phenyl and -methyl substituent effects with those found in other secondary systems provides an estimate of the anchimeric assistance in cyclopropyl tosylate solvolysis in the range 104 6-107. We conclude that methyl rather than phenyl groups are preferable as probes for detecting nonclassical charge delocalization at positions remote from the site of attachment of the leaving group. The degree of ring opening at the transition state for a given cyclopropyl system does not appear to change significantly with a change in leaving group. The rate enhancements provided by trans-/3 substituents follows the leaving group order Cl > Br > OTs; we attribute this to electronic effects. Ground-state steric effects are a significant factor in the reactivity of cis-j3 substituted cyclopropyl systems. The order of leaving group steric size in these cyclopropyl systems is Br > Cl > OTs, which parallels the van der Waals' radii of the atoms involved (Br > Cl > O). he solvolyses of cyclopropyl derivatives tend strongly to proceed with concerted disrotatory ring opening.1,3-6 At least partial ring opening is simultaneous with departure of the leaving group in almost all cases leading to a transition state in which the positive charge is delocalized over all three-ring carbon atoms; eventually ring-opened allyl products are produced.6 The effect of a change in the leaving group on the reactivity of cyclopropyl derivatives has, however, received little attention.

No abstract

Die thermische Umlagerung der isomeren Monochloride (Ia) und (Ic) führt zwar jeweils zum gleichen Produkt (II), jedoch reagieren (Ia) und (Ic) dabei nach verschiedenen Mechanismen, wie anhand kinetischer Untersuchungen der Thermolyse und Solvolyse von (Ia) und (Ic) sowie des Dichlorids (Ie) und aufgrund der Ergebnisse der analogen Thermolyse der deuterierten Verbindungen (Ib) und (Id), die die verschiedenen Dihydroindene (III) und (IV) liefert, festgestellt wird.