17009-83-5Relevant academic research and scientific papers
Chloronium Ions as Alkylating Agents in the Gas-Phase Ion-Molecule Reactions with Negative Temperature Dependence
Sharma, D. K. Sen,Kebarle, P.
, p. 19 - 24 (2007/10/02)
The kinetics of the reactions Me2Cl+ + B = MeB+ + MeCl and MeEtCl+ + B = MeB+ or (EtB+) + EtCl (or MeCl) were studied with a pulsed-electron-beam, high-pressure mass spectrometer.At room temperature the rate constants were found to increase in the order B = benzene, toluene, isopropylbenzene, EtOH, Me2O, Et2O.At this point k become equal to the orbiting capture rate constant k1 ca. 10-9 molecule-1 cm3 s-.NH3 and Me3N were alkylated at orbiting capture rates.The temperature dependence of the rate constants for B = toluene, Me2O, and Et2O was examined.The rate constants were found to increase with decrease of temperature.This increase continued until the rate constants reached the magnitude of the orbiting rate constant kL.The rates remained approximately independent of temperature below this temperature.At low temperatures the collision-stabilized Me2Cl+B and MeEtCl+B could be observed.The temperature dependence of the equilibrium Me2Cl+ + toluene = (Me2Cl-toluene)+ was measured and led to the corresponding ΔHo and ΔSo.The reaction Me2Cl+ + benzene = Me-benzene+ + MeCl was found to have positive temperature dependence.On the basis of the above data it is suggested that the reactions Me2Cl+ + B = MeB+ + MeCl have an internal barrier in the potential energy of the reaction coordinate.This barrier protrudes above the energy level of the reactants (Me2Cl+ + B) for B = benzene.This leads to positive temperature dependence.For all other B, the top of the internal barrier lies below the level of the reactants and sinks lower, roughly in the order of increasing basicity of B.This lead to negative temperature dependence (toluene, isopropylbenzene, Me2O, Et2O).For B = NH3, MeNH2, Me3N, the barrier is so low that the reactions have orbiting capture rates equal to kL.Alkylation of bases B by chloronium ions like Me2Cl+ might have considerable utility in mass spectrometric analysis by chemical ionization.Ethers can be distinguished from alcohols and tertiary amines from primary and secondary amines.The alkylated ethers and the tertiary amines have no protic hydrogens and therefore do not form strongly hydrogen-bonded adducts.
Carbon-Hydrogen Bond Dissociation Energies in Alkylbenzenes. Proton Affinities of the Radicals and the Absolute Proton Affinity Scale
Meot-Ner (Mautner), Michael
, p. 5 - 10 (2007/10/02)
Rate constants (k) were measured for proton-transfer reactions from alkylbenzene ions RH+ to a series of reference bases B, i.e., RH+ + B -> BH+ + R*.For exothermic reactions (ΔH -1.For example, the reaction C6H5CH3+ + B -> BH+ + C6H5CH2* is fast (reaction efficiency = k/kcol >/= 0.5) when B = MeO-t-Bu or stronger bases, but k/kcol is significantly smaller when B is n-Pr2O or weaker bases.From the falloff curve of reaction efficiency vs.PA(B), we find PA(n-Pr2O) = PA(C6H5CH2*) + 0.8 kcal mol-1 = 200.0 kcal mol-1.Since PA(C6H5CH2*) is obtained from known thermochemical data, this relation defines the absolute PA of n-Pr2O.Through a ladder of known PA, we then obtain PA(i-C4H8) = 186.8 kcal mol-1; we also obtain the absolute PAs of other oxygen bases.Falloff curves of reaction efficiencies of 3-FC6H4CH3+, C6H5C2H5+, C6H5-n-C3H7+, and C6H5-i-C3H7+ with these reference bases give then the following PAs of R* and R-H bond dissociation energies (Do) (all in kcal mol-1) as R*, PA(R*), Do(R-H): 3-FC6H4CH2*, 197.2, 89.4; , 197.9, 86.2; , 199.1, 86.1; , 199.6, 86.1.In similar manner, rate constants for H+ transfer from C6H5NH2+ to reference pyridines and amines yield PA(C6H5NH*) = 221.5 and Do(C6H5NH-H) = 85.1 kcal mol-1 (1 kcal mol-1 = 4.18 kJ mol-1).
Oxonium Ions. Solvation by Single Acetonitrile Molecules in the Gas Phase and by Bulk Solvents
Bromilow, J.,Abboud, J. L. M.,Lebrilla, C. B.,Taft, R. W.,Scorrano, G.,Lucchini V.
, p. 5448 - 5453 (2007/10/02)
The standard free energy of formation of gaseous complexes between monoprotonic oxonium ions and acetonitrile have been obtained by using the ion cyclotron resonance equilibrium constant method for exchange of acetonitrile between the ions.The results show that the "solvation" by a single molecule of acetonitrile in the gas phase reproduces the important diverse effects of molecular structure on oxonium ion solvation by bulk water.It is estimated from the present results that the effects of solvation by bulk water are only about three times as great as the corresponding effects of "solvation" by a single water molecule in the gas phase.Internal charge delocalization from the protonic site of the oxonium ions may be reversed by differential solvation, both with single H-bonding molecules in the gas phase and with bulk solvent.Further evidence for the site of preffered protonation of esters and amides is provided.
