56954-90-6Relevant academic research and scientific papers
COMPETING SOLVOLYTIC SUBSTITUTION AND ELIMINATION REACTIONS VIA A COMMON IRREVERSIBLY FORMED ION-MOLECULE PAIR INTERMEDIATE
Sidhu, Harvinder,Thibblin, Alf
, p. 578 - 584 (2007/10/02)
The acid-catalysed solvolysis of 9-(2-phenoxy-2-propyl)fluorene in mixtures of water with acetonitrile or methanol at 25 deg C provides 9-(2-hydroxy-2-propyl)fluorene, 9-(2-propenyl)fluorene, and 9-(2-acetamido-2-propyl)fluorene or 9-(2-methoxy-2-propyl)fluorene, respectively.The overall kinetic deuterium isotope effects for the reactions of the hexadeuterated analogue 9-(1,1,1,3,3,3-2H6)-9-(2-phenoxy-2-propyl)fluorene in 90 vol.percent acetonitrile in water were measured as (kEH+kSH)/(kED6+kSD6)=1.54+/-0.05, which is composed of the isotope effect kSH/kSD6=1.4+/-0.1 for formation of the substitution products and kEH/kED6=4.0+/-0.2 for production of 9-(2-methoxy-2-propyl)fluorene.Similar isotope effects were measured in other solvent mixtures.The results strongly indicate a branched mechanism involving rate-limiting formation of a common carbocation-molecule pair (with a secondary isotope effect of 1.54), which either undergoes nucleophilic attack by a solvent molecule (with a secondary isotope effect of ca 1), or is dehydronated (isotope effect ca 2.8) by the leaving group or by the solvent.The ion-molecule pair shows very low selectivities.Thus, in 50 vol.percent acetonitrile in water, an acetonitrile molecule is as efficient as a water molecule as a nucleophile towards the ion-molecule pair, kMeCN/kHOH>/=1 (ratio of second-order rate constants).The discrimination between methanol and water is anomalously small, kMeOH/kHOH=0.7.
Deprotonation of Ion Pairs in Aqueous Solvent. Competing Bimolecular and Solvolytic Elimination Reactions
Thibblin, Alf
, p. 2071 - 2076 (2007/10/02)
Solvolysis of 9-(2-chloro-2-propyl)fluorene (h-1-Cl) or 9-(2-bromo-2-propyl)fluorene (h-1-Br) in 25 vol percent acetonitrile in water at 25 deg C produces 9-(2-propenyl)fluorene (h-4), 9-(2-hydroxy-2-propyl)fluorene (h-2), and a trace of 9-isopropylidenefluorene (h-3).The corresponding acetate 9-(2-acetoxy-2-propyl)fluorene (h-1-OAc) yields the same products but comparable amounts of 3 and 4.The presence of base as well as chloride or bromide ions increases the fraction of elimination products but does not increase k12 + k14.The Broensted parameter for deprotonation of the carbocationic intermediate with substituted acetate anions is small, β = 0.05.The deuteriated analogue 9-(1,1,1,3,3,3-2H6)-9-(2-chloro-2-propyl)fluorence (d6-1-Cl) reacts slower than h-1-Cl.Thus, the overall kinetic isotope effect was measured without base as (k12H + k13H + k14H)/(k12d6 + k13d6 + k14d6) = 2.2 +/- 0.1, which is composed of the isotope effect k12H/k12d6 = 1.4 +/- 0.1 for formation of the substitution product 2 and k14H/k14d6 = 3.7 +/- 0.3 for production of the olefin 4.The results indicate a branched mechanism involving rate-limiting formation of a common contact ion pair (with a secondary isotope effect of 2.2) which either undergoes nucleophilic attack by water (isotope effect 1.0) or is deprotonated by water (isotope effect 2.8) or other general base (including chloride and bromide anions).Direct elimination from the ion pairs is indicted by the observation that the fraction of elimination increases with rising basicity of the leaving group.The intermediate shows very small discrimination between the nucleophiles azide anion, mathanol, and water.The presence of strong base in the reaction solution opens up a parallel bimolecular elimination route (E1cB or E2) for 1-Cl.Thus 0.16M sodium hydroxide yields mainly 3 but the rates of formation of the solvolysis products 2 and 4 are decreased only slightly.The (9-2H) analogue d-1-Cl, which solvolyzes 3percent slower than h-1-Cl, undergoes hydroxide-promoted elimination with an isotope effect k13H/k13D of 8.1.
Electrochemical Studies of the Reduction of 6,6-Dimethyldibenzofulvene Oxide and Tetraphenyloxirane
Nuntnarumit, C.,Null, W. Edward,Hawley, M. Dale
, p. 4827 - 4833 (2007/10/02)
The electrochemical reduction of 6,6-dimethyldibenzofulvene oxide (1) in dimethylformamide-0.1 M (n-Bu)4NClO4 is an overall two-electron process that affords 9-fluorenyl anion and acetone in the absence of an added proton donor and 2-(9-fluorenyl)propanol (2) in the presence of diethyl malonate.The initial electroreduction of tetraphenyloxirane (3) is also a two-electron process and gives Ph2C(-)CPh2(O-) as an unobserved intermediate.This dianioon reacts rapidly by abstracting a proton at either the benzhydryl carbon center (75percent) or the oxygen center (25percent) to give either Ph2CHCPh2(O-) or Ph2C(-)CPh2OH.The former anion then undergoes an elimination of Ph2CH(-) to afford Ph2C=O whereas Ph2C(-)CPh2(OH) eleminate OH- to give Ph2C=CPh2.Ph2C=O and Ph2C=CPh2 are then reduced at the applied potential to Ph2CHOH and (Ph2CH)2, respectively.Ph2CHCPh2OH (4) and 2 undergo electrochemically induced chain reactions in the potential range of interest with 4, affording equimolar amounts of Ph2C=O and Ph2CH2, whereas 2 gives equimolar amounts of fluorene and acetone.There is no evidence that carbene anion radicals are formed as transient intermediates in any of the electroreductions.
Studies of the Borderline between Concerted and Stepwise Mechanisms of Elimination : E1cB Elimination of Fluoren-9-ylmethyl Carboxylate Esters
O'Ferrall, Rory A. More,Larkin, Finbar,Walsh, Peter
, p. 1573 - 1580 (2007/10/02)
Rates of β-elimination of carboxylate leaving groups from fluoren-9-ylmethyl carboxylate esters in methanolic sodium methoxide at 25 deg C are reported.An E1cB mechanism with rate-determining formation of a carbanion intermediate is assigned on the basis of near identity of measured elimination rates and rates of carbanion formation predicted from a Taft correlation, and the similarity with elimination of 1-(1-acetoxy-1-methylethyl)indene for which the mechanism has been established by Ahlberg and Thibblin.Values of ρ=0.42 and βlg=0.27 measured for substituted benzoate leaving groups are a little larger than expected (ca. 0.24 and 0.18, respectively) and the discrepancy is tentatively ascribed to conformational enhancement of remote substituent effects, rather than to a contribution of E2 elimination.The effects of alkyl and aryl substitution α to the leaving group are discussed, especially in relation to the borderline between concerted and stepwise mechanisms.The measurements fail to confirm an earlier inference that the borderline shows a discontinuity in transition-state structure at the point of mechanistic change.
