title: Substituent Effects on the Formation and Nucleophile Selectivity of Ring-Substituted Phenonium Ions in Aqueous Solution.
abstract: The reaction of 2-(4-methyphenyl)ethyl tosylate (Me-1-OTs) in 50/50 (v/v) trifluoroethanol/water at 25 °C is first-order in the concentration of azide anion nucleophile. A carbon-13 NMR analysis of the products of the reactions ofMe-1-[α-13C]OTsin 50/50 (v/v) trifluoroethanol/water at 25 °C shows the formation ofMe-1-[β-13C]OH,Me-1-[β-13C]OCH2CF3andMe-1-[β-13C]N3from the trapping of a symmetrical 4-methylphenonium ion reaction intermediateMe-2+. The formation ofMe-1-[α-13C]N3by concerted bimolecular displacement of azide ion atMe-1-[α-13C]OTs(kN= 3.8 × 10-6M-1s-1) and ofMe-1-[α-13C]OHandMe-1-[α-13C]OCH2CF3by concerted bimolecular displacement of solvent (ksolv= 1.8 × 10-8s-1) is also observed. An analysis of the rate and product data provides a value ofkaz/ks= 32 M-1for partitioning ofMe-2+between addition of azide ion and solvent that is nearly 3-fold smaller thankaz/ks= 83 M-1reported in an earlier study on the partitioning ofMeO-2+[J. Org. Chem.2011,76, 9568]. This change is attributed to a decrease in nucleophile selectivity with increasing electrophile reactivity for the activation-limited addition of solvent and azide anion toX-2+. These data set a limit of 1/ks≥ 10-7s for the lifetime ofMe-2+in aqueous solution.
authors: Department of Biochemistry and Applied Chemistry, Kurume National College of Technology, Komorinomachi, Kurume 830-8555, Japan.
authors: Yutaka
authors: Y
authors: Tsuji
authors: Department of Biochemistry and Applied Chemistry, Kurume National College of Technology, Komorinomachi, Kurume 830-8555, Japan.
authors: Shin
authors: S
authors: Ogawa
authors: Department of Chemistry, University at Buffalo, SUNY, Buffalo, NY 14260, USA.
authors: John P
authors: JP
authors: Richard