102101-28-0Relevant articles and documents
Intra- and Inter-molecular Hydron Abstraction from Allylic Carbocation Intermediates in Aqueous Solvent. Observation of a Substantial Deuterium Isotope Effect for 1,4-Elimination of Acetic Acid from One of the Ion-pair Intermediates
Thibblin, Alf
, p. 321 - 326 (1986)
The allylic carbocation intermediate formed from 3-(2-chloropropan-2-yl)indene (1-Cl) and from (1,1-2H2)-(1-Cl) in 75 vol percent water-acetonitrile at 35 deg C reacts rapidly with solvent water to give the allylic alcohols but is also subject to hydron abstraction by general bases to produce 1-isopropylideneindene (3) and 3-isopropenylindene (4).The Bronsted parameters measured with substituted acetate anions were found to be small, β 0.16 for formation of (3) and 0.14 for production of (4).The kinetic deuterium isotope effect on hydron abstraction from the intermediate with acetate anion to form the olefin (3) (kH/kD) is 3.0 +/- 0.4.The corresponding intramolecular elimination of acetic acid from the contact ion pair formed from 3-(2-acetoxypropan-2-yl)indene (1-OAc) to yield (3) shows a substantial isotope effect, kH/kD = 5.2 +/- 1.0.The allylic isomer 2-acetoxy-1-isopropylideneindan (2-OAC) yields a contact ion pair that reacts to give (3) with a considerably smaller isotope effect, kH/kD = 2.9 +/- 0.3.The free carbocation generated from protonated 3-(2-hydroxypropan-2-yl)indene (1-OH) and its (1,1-2H2)-analogue undergo hydron abstraction to give the olefin (3) with an isotope effect kH/kD = 4.1 +/- 0.3.These isotope effects do not include the isotope effect on the rate-limiting ionization step, which were found to be kH/kD = 1.07 and 1.22 in the reactions of (1-OAc) and (2-OAc), respectively.The elimination isotope effects for the ion pairs are evaluated by assuming that the formation of alcohols from the intermediates has an isotope effect of unity.
