Sterochemistry of Allylic Rearrangements. II. The Kinetics and Stereochemistry of the Rearrangement of cis- and trans-5-Methyl-2-cyclohexenyl Acid Phthalate¹

Solvolytic Displacement Reactions At Saturated Carbon Atoms

“…Studies have also been made of the solvolyses of hydrogen cis-and trans-5-methylcyclohexenyl-3 phthalates in aqueous acetone (279) and in acetonitrile (277) solutions. The phenomenon of internal return was observed in both solvent systems.…”

Ion Pair Dynamics: Solvolyses of Chiral 1,3-Diarylallyl Carboxylates as a Case Study

“…Since the cis / trans isomerization of optically active cis - and trans -5-methylcyclohex-2-enyl 2-carboxybenzoates ( A ⇌ B , LG = OPht, Scheme ) in acetonitrile was found to proceed significantly more slowly than the racemization (( S )- A ⇌( R )- A ; ( S )- B ⇌( R )- B ), Goering proposed the formation of ion pair intermediates ( C , D ), in which the anion remains on the same face of the allyl cation as in the substrate. The collapse of these ion pairs (internal return) either regenerates the starting materials or leads to their enantiomers by attack of the anion at the other allylic terminus.…”

“…The collapse of these ion pairs (internal return) either regenerates the starting materials or leads to their enantiomers by attack of the anion at the other allylic terminus. The cis / trans isomerization, which requires the migration of the leaving group (LG) to the other face of the allyl cation, was proposed to proceed via dissociation of the initial ion pairs to an achiral carbocationic intermediate ( E ) that can be attacked by the LG from both faces (Scheme ) …”

“…21a,22,23 Goering's pioneering investigations of the transformations of optically active allyl derivatives by titrimetric and polarimetric methods as well as product analyses including isotope exchange experiments have become textbook examples 24 to demonstrate the role of ion-pairing in S N 1 reactions. Since the cis/trans isomerization of optically active cis-and trans-5-methylcyclohex-2-enyl 2-carboxybenzoates (A⇌B, LG = OPht, Scheme 1) in acetonitrile was found to proceed significantly more slowly than the racemization ((S)-A⇌(R)-A; (S)-B⇌(R)-B), 25 Goering proposed the formation of ion pair intermediates (C, D), in which the anion remains on the same face of the allyl cation as in the substrate. The collapse of these ion pairs (internal return) either regenerates the starting materials or leads to their enantiomers by attack of the anion at the other allylic terminus.…”

SALT EFFECTS ON NON-ELECTROLYTES IN PARTIALLY AQUEOUS MIXED SOLVENTS1

“…The data show that the salting order of various electrolytes in 50% dioxane is quite different from that generally observed in water. 3 This can be seen by comparing the values of k in Table I, which were obtained by plotting log versus Cs and measuring the slope. A positive k is associated with salting-out while a negative k results from salting-in of the non-electrolyte by the salts present.…”