20168-37-0Relevant academic research and scientific papers
The molecularity of the Newman-Kwart rearrangement
Burns, Matthew,Lloyd-Jones, Guy C.,Moseley, Jonathan D.,Renny, Joseph S.
supporting information; experimental part, p. 6347 - 6353 (2010/12/19)
It was recently reported that the venerable Newman-Kwart rearrangement (1→2) proceeds via mixed first- and second-order kinetics. Prior to this, the rearrangement had been considered to proceed exclusively via an intramolecular OAr→SAr migration. A new bimolecular pathway, possibly involving an 8-membered cyclic transition state, was proposed to account for reaction rates that increased disproportionately with substrate concentration under microwave heating conditions. We report a reanalysis of the kinetics and molecularity of the rearrangement of N,N-dimethyl O-(p-nitrophenyl)thiocarbamate 1a in N,N-dimethylacetamide solvent. Using HPLC, isotopic labeling (2H, 18O, 34S), and ESI-ICRMS methods, we show that there is no evidence for a bimolecular pathway en route to 2a, with near-perfect exponential decay in 1a at concentrations ranging from 0.11 to 4.70 M. Instead, it is demonstrated that under the microwave heating conditions, a delayed negative feedback signal to the microwave power balancing loop results in oscillatory reaction overheating. Due to higher tan δ in the solute, the amplitude of this oscillation increases with the concentration of 1a, and this phenomenon best accounts for the kinetic behavior previously misinterpreted as being mixed 'irst- and second-order in nature.
Examination of P-OR bridging bond orders in phosphate monoesters using 18O isotope shifts in 31P NMR
Sorensen-Stowell, Kerensa,Hengge, Alvan C.
, p. 4805 - 4809 (2007/10/03)
Evidence indicates that phosphate monoesters undergo hydrolysis by a loose transition state with extensive bond fission to the leaving group. It has been proposed that part of the high dependence of the rate on the leaving group pKa (βlg/
Synthesis and NMR spectroscopy of stable isotope-labelled phenols and L-tyrosines
Winkel, C.,Aarts, M. W. M. M.,Heide, F. R. van der,Buitenhuis, E. G.,Lugtenburg, J.
, p. 139 - 146 (2007/10/02)
The syntheses of (17O)phenol from (17O)water, (18O)phenol from (18O)water, (1-13C)-phenol and (4-13C)phenol from (2-13C)acetone and (2-13C)phenol and (3-13C)phenol from (1-13C)acetone with high isotopic enrichment are described.The labelled phenols are converted into their corresponding L-tyrosines by the bacterium Erwinia herbicola.A full analysis of the 1H and 13C NMR spectra of phenol and L-tyrosine is reported.
(18)O and Secondary (2)H Kinetic Isotope Effects Confirm the Existence of Two Pathways for AAcid-caatalysed Hydrolyses of α-Arabinofuranosides
Bennet, Andrew J.,Sinnott, Michael L.,Wijesundera, W. S. Sulochana
, p. 1233 - 1236 (2007/10/02)
The (18)O kinetic isotope effect on the HClO4-catalysed hydrolysis of 4-nitrophenyl -α-arabinofuranoside (k16/k18)is 1.023 +/- 0.003 at 80.0 deg C; that for isopropyl -α-arabinofuranoside is 0.988 at 30.2 deg C and the secondary deuterium effect on the hydrolysis of propan-2-yl α-arabinofuranoside (kH/kD) is 0.979.The nitrophenyl glycoside reaacts with exocyclic C-O cleavage and the propaan-2-yl glycoside by endocyclic C-O cleavage.
