618-11-1Relevant academic research and scientific papers
Carbocation-forming reactions in ionic liquids
Creary, Xavier,Willis, Elizabeth D.,Gagnon, Madeleine
, p. 18114 - 18120 (2007/10/03)
A number of trifluoroacetates, mesylates, and triflates have been studied in ionic liquids. Several lines of evidence indicate that all of these substrates react via ionization to give carbocationic intermediates. For example, cumyl trifluoroacetates give mainly the elimination products, but the Hammett ρ+ value of -3.74 is consistent with a carbocationic process. The analogous exo-2-phenyl-endo-3-deutero-endo-bicyclo-[2.2.1]hept-2-yl trifluoroacetate gives an elimination where loss of the exo-hydrogen occurs from a cationic intermediate. 1-Adamantyl mesylate and 2-adamantyl triflate react to give simple substitution products derived from capture of 1- and 2-adamantyl carbocations by the residual water in the ionic liquid. The triflate derivative of pivaloin, trans-2-phenylcyclopropylcarbinyl mesylate, 2,2-dimethoxycyclobutyl triflate, the mesylate derivative of diethyl (phenylhydroxymethyl)-thiophosphonate, and Z-1-phenyl-5-trimethylsilyl-3-penten- 1-yl trifluoroacetate all give products derived carbocation rearrangements (kΔ processes), anti-7-Norbornenyl mesylate gives products with complete retention of configuration, indicative of involvement of the delocalized 7-norbornenyl cation. 1,6-Methano[10]annulen-11-yl triflate reacts in [BMIM][NTf2] to give 1,6-methano[10]annulen-11-ol, along with naphthalene, an oxidized product derived from loss of trifluoromethanesulfinate ion. Analogous loss of CF3SO2- can be seen in reaction of PhCH(CF3)OTf. Ionic liquids are therefore viable solvents for formation of carbocationic intermediates via kc and k Δ processes.
Electronic Effects on Triplet and Singlet Excited-State Carbonyl Formation in the Thermolysis 3-Aryl-3-methyl-1,2-dioxetanes
Richardson, William H.,Stiggal-Estberg, Diana L.
, p. 4173 - 4179 (2007/10/02)
A series of para- and meta-substituted 3-aryl-3-methyl-1,2-dioxetanes (1) was studied in order to evaluate the electronic effect of substituents on the efficiencies of excited-state carbonyl production.All substituents reduced the efficiency of triplet carbonyl production.Several correlations point to the formation of a triplet carbonyl exciplex, originating from a triplet biradical, in the thermolysis of 1.It also appears that substituent variation in the proacetophenone portion of 1 results in triplet efficiency changes primarily in formaldehyde, which can be rationalized in terms of a triplet exciplex.Substituent effects on singlet (S1) efficiency are markedly different from those observed with triplet efficiencies.The possibility of heavy-atom effects in 1 was pursued with p-Br and m-Br substituents.No detectable heavy-atom effect was observed with singlet (S1) efficiencies, but the p-Br substituent appeared to decrease the triplet efficiency.This suggests that a p-Br heavy-atom effect may operate from the triplet exciplex, providing the approximations used in the evaluations of the heavy-atom effect are valid.The effect of substituents on rate of thermolysis of 1 provides further evidence for a biradical mechanism.
ADDITIONS OF SUBSTITUTED PHENYLTHIYL RADICALS TO SUBSTITUTED α-METHYLSTYRENES. GROUND STATE AND TRANSITION STATE ELECTRONIC EFFECTS
Geers, Brian N.,Gleicher, Gerald Jay,Church, Daniel F.
, p. 997 - 1000 (2007/10/02)
The radical addition of substituted thiophenols to α-methylstyrene and substituted α-methylstyrenes has been investigated at 70 deg C.Relative reactivities of pairs of thiophenols competing with individual alkenes can be utilized to obtain Hammett correlations.The interplay of substituent effects in alkene and thiyl radical leads to examples of non-linear rho values.Rationales for this behavior will be offered in terms of variable contributions from ground state and transition state electronic factors as well as in terms of possible mechanistic changes.
