19656-59-8Relevant academic research and scientific papers
The Role of Single-Electron Transfer in SN2-Type Substitution Reactions of Anions with Alkyl Halides
Bordwell, F.G.,Harrelson, John A.
, p. 4893 - 4898 (2007/10/02)
Rate constants (kobsd) for reactions of electrophiles with: (a) various carbanions, including 9-substituted fluorenide ions (9-GFl-), 9-substituted xanthenide ions, α-cyano carbanions, anb β-diketo enolate ions, (b) phenothiazinide (PTZ-) and carbazole (Cb-) nitranions, (c) 4-substituted phenoxide ions, and (d) thiphenoxide ions, have been campared with rate constants for single-electron transfer (kSET) calculated using a Marcus-type equation.For both 9-GFl- carbanion and 2-GPTZ- nitranion families reacting with SET acceptors, such as 1,1-dinitrocyclohexane, the kobsd/kSET ratio is near unity.For 9-GFl- carbanions reacting with Ph2CHCl the kobsd/kSET ratios range from 2 to 105, those for 2-PTZ- nitranions from 370 to 1.3*104, and those for Cb- nitranions from 108 to 1010.For reactions of 4-GC6H4O- oxanions with Ph2CHCl the ratios range from 103 for G = Me2N to 1013 for G = CN; for PhS- ion reacting with n-BuBr the ratio is 1017.The significance of these results with respect to the role of an outer sphere SET mechanism in substitution reactions of anions with alkyl halides is discussed.
Reactions of 9-Substituted Fluorenide Carbanions with Allyl Chlorides by SN2 and SN2' Mechanism
Bordwell, Frederick G.,Clemens, Anthony H.,Cheng, Jin-Pei
, p. 1773 - 1782 (2007/10/02)
The average ratio of SN2 rate constants for benzyl chloride vs. allyl chloride reacting with 9-substituted fluorenide carbanions, 9-G-Fl- (G = Me, PhS, Ph o-tol, or t-Bu), in Me2SO solution is 2.3, which is close to the ratio previously observed for reactions of smaller nucleophiles with more localized charges, such as iodide ion, in various solvents.Broensted plots of log k vs. pKHA (both in Me2SO) are used to calculate reactivity values (r) for 9-G-Fl- ions of the same basicity reacting with allyl chloride.The r values reveal the same order of steric effects for G in these SN2 reactions as was found previously for benzyl chloride, i.e., Me - ions were found to increase progressively and appreciably with γ-methyl substitution, i.e., CH2=CHCH2Cl (1) , MeCH=CHCH2Cl (4) , Me2C=CHCH2Cl (5), whereas the Broensted β values decreased progressively.The second-order rate constants for reactions with families of 9-G-Fl- ions were found to follow a somewhat different pattern for α-methyl substitution, i.e., CH2=CHCH2Cl (1) > CH2=CHCH(Me)Cl (2) CH2=CHC(Me)2Cl (3); the rate differences were small, but the β values again decreased progressively.Product studies indicated that 1 reacts with 9-G-Fl- ions by an SN2 mechanism but that 2 gives SN2' products in a amounts increasing along the series G = Me, Ph, o-tol, t-Bu; 3 appears to give only SN2' products.The rates of reactions of 9-CN-Fl- and 9-CO2MeFl- ions with 3 to form SN2' and SN2 products are independent of the carbanion concentration.The first-order reaction of 9-CN-Fl- ion with t-BuCl in MeOH gives 17percent yield of 9-CN-9-t-BuFl.Entalpies of activation for SN2 reactions of 9-G-Fl- ions reacting with 5 are 7-9 kcal/mol lower, and entropies of activation are 18, or more, eu units less positive than for SN2' reactions of 9-G-Fl- ions with 3.Mechanism for SN2' reactions are discussed in light of these findings.
A Direct Relationship between Nucleophilicity and Basicity in SN2 Reactions of Fluorenyl Anions with Benzyl Chloride in Dimethyl Sulfoxide Solution
Bordwell, Frederick G.,Hughes, David L.
, p. 3314 - 3320 (2007/10/02)
The rates of reactions for nine 9-substituted fluorenyl anions, 9-G-Fl- (G=CN, CO2Me, PhSO2, PhS, Ph, PhO, PhCH2, Me, t-Bu), reacting with benzyl chloride in Me2SO solution have been measured.For 9-CN-Fl- the rates increased with sol
Hammett and Broensted-Type Relationships in Reactions of 9-Substituted Fluorenyl Anions with Benzyl Halides
Bordwell, Frederick G.,Hughes, David L.
, p. 3320 - 3325 (2007/10/02)
The rates of reaction of 9-substituted fluorenyl anions, 9-G-Fl- (G=CN, Ph, Me), with substituted benzyl chlorides (p-MeO, p-Me, m-Me, p-F, p-Cl, m-Cl, m-CF3, m-NO2) in Me2SO solution have been measured.A "U-shaped" Hammett plot was obtained for 9-CN-Fl- (ρmeta 1.3), but a "normal" Hammett plot was obtained with 9-Ph-Fl- (ρ = 1.8), which is 9.6 pK units more basic.Broensted-type plots of log k vs. pKa obtained for three 9-G-Fl- families (9-PhSO2, 9-PhS, and 9-Ph) reacting with m-CF3C6H4CH2Cl gave slopes (βNu) near 0.4.The βNu values for the 9-Ph-Fl- family reacting with ArCH2Cl were increased by the presence of electron accepting substituents, p-MeO (0.30), H (0.365), m-CF3 (0.45), m-NO2 (0.485).The small increases in Hammett ρ values and βNu values caused by electron-withdrawing substituents in ArCH2Cl are interpreted to mean that there is a small increase in the negative charge density in the benzylic carbon atom and/or chlorine atom in the transition state.Rates for the reaction of PhCH2Br with eight 9-G-Fl- anions were measured.For 9-CN-Fl- the kBr/kCl rate ratio was found to be 4 times larger in Me2SO than in EtOH.The reactivity-selectivity principle is discussed and the conclusion drawn that it should be abandoned.
