17000-01-0Relevant articles and documents
Endothermic Proton Transfer Reactions from Three +. Isomers
Kinter, Michael T.,Bursey, Maurice M.
, p. 775 - 778 (1987)
A triple quadrupole mass spectrometer was used to establish the proton affininties of phenyl, CH3CCCCCH2., and HCCCH2CH.CCH radicals as 870 +/- 29, 824 +/- 25, and 757 +/- 21 kJ mol-1, respectively, from the kinetic energy of benzene, 2,4-hexadiyne, and 1,5-hexadiyne molecular ions at which the onset of proton transfer to less basic species occurs in the second rod assembly.These values were confirmed by other triple quadrupole experiments involving bracketing of exothermic proton transfers.
Solvolysis of N,N-dimethylthiocarbamoyl chloride: Effect of sulfur-for-oxygen substitution upon kinetics and product partitioning
Kevill, Dennis N.,Rudolph, Todd M.,D'Souza, Malcolm J.
, p. 192 - 196 (2000)
A study of the solvolyses of N,N-dimethylcarbamoyl chloride (1) was extended to the solvolyses of N,N-dimethylthiocarbamoyl chloride (2). The specific rates of solvolysis of 2 at 0.0°C are two to three orders of magnitude greater than those for 1. Analysis of the data using the extended Grunwald-Winstein equation leads to sensitivities l and m and an l/m ratio which are lower for 2 than those previously reported for 1. Product selectivities in mixtures of water with ethanol or methanol indicate a greater preference for reaction with alcohol for 2. All observations can be rationalized in terms of the formation of a more stable carbocation from 2, leading to an earlier transition state, reduced nucleophilic solvation and the possibility of extensive progression to a free carbocation prior to product formation. Copyright
Thermochemistry of Silaethylene and Methylsilylene from Experiment and Theory
Shin, Seung Koo,Irikura, Karl K.,Beauchamp, J. L.,Goddard, William A.
, p. 24 - 30 (2007/10/02)
Fourier transform ion cyclotron resonance spectroscopy has been used to examine the deprotonation energetics of the methylsilyl cation, CH3SiD2+, to yield silaethylene and methylsilylene proton affinities of 205 +/- 3 and 215 +/- 4 kcal/mol, respectively.These values combined with the known heat of formation of methylsilyl cation, yield ΔHof 298(CH2SiH2) = 43 +/- 3 kcal/mol and ΔHof 298(CH3SiH) = 53 +/- 4 kcal/mol.These results are corroborated by ab initio generalized valence bond-configuration interaction calculations which indicate that silaethylene is more stable than methylsilylene by 11.6 kcal/mol, in excellent agreement with the experimental difference (10 +/- 3 kcal/mol).The adiabatic ionization potential of methylsilylene is calculated to be 8.22 eV, which is lower than the value of 8.85 eV determined for silaethyene using photoelectron spectroscopy.
Catalysis of Transimination by Rate-Limiting Proton Transfer to Buffer Bases
Fischer, Helene,DeCandis, Francis X.,Ogden, Sharon D.,Jencks, William P.
, p. 1340 - 1347 (2007/10/02)
General base catalysis of the hydroxylamonilysis of benzhydrylidenedimethylammonium ion gives a Broensted plot that follows the Eigen curve expected for rate-determining trapping of the initially formed addition intermediate by proton transfer to a buffer base or water.The solvent deuterium isotope effects for catalysis by oxy anions exhibit a maximum at the break point of the Eigen curve, close to the estimated pKa for the addition intermediate.This maximum can be accounted for by a partial change in rate-limiting step of the proton-transfer process near ΔpK = 0.Water shows a positive deviation from the Broensted plot and a solvent isotope effect of kH2O/kD2O = 4.7 that provide additional evidence for the trapping mechanism.The addition of glycerol increases the rate of the base-catalyzed reaction; much larger increases are observed with ethylene glycol and methanol.In contrast, the base-catalyzed hydrolysis of the cationic imine follows a linear Broensted plot (β = 0.24), with a negative deviation for catalysis by water, and gives a constant value of kH2O/kD2O = 1.9 +/- 0.2.A concerted mechanism of base-catalyzed attack by water is suggested for this reaction.
Phosphoranes. 3. New tris(trifluoromethyl)phosphoranes (CF3)3PXY with monofunctional [F, Cl, N(CH3)2, OCH3, SCH3, OSi(CH3)3] substituents
The, Kwat I.,Cavell, Ronald G.
, p. 2518 - 2525 (2007/10/12)
New five-coordinate molecular phosphoranes of the types (CF3)3PY2 (Y = OCH3) and (CF3)3P(F)Y (Y = N(CH3)2, OCH3, SCH3, OSi(CH3)3) have been prepared from (CF3)3PF2 and the trimethylsilyl reagent (CH3)3SiY or dimethylamine. An improved synthesis of (CF3)3P(Cl)N(CH3)2 is also described. Formulation of the monofluoro- and disubstituted phosphoranes as the isomeric phosphonium salts can be clearly ruled out by NMR spectroscopic studies. At low temperatures, 19F, 31P, and, in the case of (CF3)3P(Cl)N(CH3)2, 13C NMR spectra of the phosphoranes show the presence of different CF3 environments consistent with substitution at axial or equatorial positions of the (assumed) trigonal-bipyramidal framework. The former are characterized by relatively small 2JPF and the latter by relatively large 2JPF values. Ground-state structures are consistent with the preferential location of halogen (F, Cl) in the axial positions and of OCH3, SCH3, or N(CH3)2 groups in the equatorial positions. The CF3 groups which occupy the remaining axial and equatorial sites are, in most cases, distinguishable by 19F NMR with only moderate cooling of the sample. New 31P NMR data for (CF3)3P[N(CH3)2]2 strongly support the location of both N(CH3)2 groups in the equatorial plane as suggested earlier. The barrier to the averaging of CF3 environments appears to decrease in the order N(CH3)2 > SCH3 > OCH3. The presence of a halogen substituent appears to lower the barrier to the averaging process compared to the doubly substituted molecules and a chlorophosphorane appears to have a lower barrier than the corresponding fluorophosphorane.
