Proton bimolecular

It is possible to detemiine the equilibrium constant, K, for the bimolecular reaction involving gas-phase ions and neutral molecules in the ion source of a mass spectrometer [18]. These measurements have generally focused on tln-ee properties, proton affinity (or gas-phase basicity) [19, 20], gas-phase acidity [H] and solvation enthalpies (and free energies) [22, 23] ... 

In an earlier section, measurements were described in which the equilibrium constant, K, for bimolecular reactions involving gas-phase ions and neutral molecules were detennined. Another method for detemiining the proton or other affinity of a molecule is the bracketing method [ ]. The principle of this approach is quite straightforward. Let us again take the case of a proton affinity detemiination as an example. In a reaction... 

The molecularity of an elementary step is given by the number of species that undergo a chemical change m that step Transfer of a proton from hydrogen chloride to tert butyl alcohol is bimolecular because two molecules [HCl and (CH3)3COH] undergo chemical change... 

Bromide ion forms a bond to the primary carbon by pushing off a water molecule This step IS bimolecular because it involves both bromide and heptyloxonium ion Step 2 IS slower than the proton transfer m step 1 so it is rate determining Using Ingold s ter mmology we classify nucleophilic substitutions that have a bimolecular rate determining step by the mechanistic symbol Sn2... 

Transition metals have also been inserted into the aziridine ring affording derivatives (295). Stereochemical studies suggest that transfer of a proton is followed by bimolecular attack on the ring with subsequent closure on the carbonyl group (76AG(E)495). 

As depicted, the E2 mechanism involves a bimolecular transition state in which removal of a proton to the leaving group is concerted with departure of the leaving group. In contrast, the rate-determining step in the El mechanism is the unimolecular ionization of... 

Elimination bimolecular (E2) mechanism (Section 5.15) Mechanism for elimination of alkyl halides characterized by a transition state in which the attacking base removes a proton at the same time that the bond to the halide leaving group is broken. 

High-boiling products found in this procedure and in similar experiments involving cyclohex-2-enone derivatives5 probably result from bimolecular reduction processes.15 3-Methylcyclohexanone, which arises by protonation rather than alkylation of the enolate (and which made up ca. 12% of the volatile products), is probably the result of reaction of allyl bromide with liquid ammonia to form the acidic species allyl ammonium bromide.5 10... 

In the E2 mechanism (elimination, bimolecular), the two groups depart simultaneously, with the proton being pulled off by a base ... 

The origin of the sequence corresponding to protonated methanol peaks is a rapid intracluster proton transfer reaction following ionization of the neutral clusters. This reaction has a well-known bimolecular counterpart that proceeds at near collision rate 104... 

Bimolecular reactions with paramagnetic species, heavy atoms, some molecules, compounds, or quantum dots refer to the first group (1). The second group (2) includes electron transfer reactions, exciplex and excimer formations, and proton transfer. To the last group (3), we ascribe the reactions, in which quenching of fluorescence occurs due to radiative and nonradiative transfer of excitation energy from the fluorescent donor to another particle - energy acceptor. 

Micellar rate enhancements of bimolecular, non-solvolytic reactions are due largely to increased reactant concentrations at the micellar surface, and micelles should favor third- over second-order reactions. The benzidine rearrangement typically proceeds through a two-proton transition state (Shine, 1967 Banthorpe, 1979). The first step is a reversible pre-equilibrium and in the second step proton transfer may be concerted with N—N bond breaking (17) (Bunton and Rubin, 1976 Shine et al., 1982). Electron-donating substituents permit incursion of a one-proton mechanism, probably involving a pre-equilibrium step. 

The values obtained for the proton transfer in these four systems (Table IV) are typically as expected for these rapid processes. Examples from the literature where similar reactions were studied in metal complexes include the [Cr(OH)(OH2)]2+ (62) and [VO(OH2)5]2+ (63) systems. In the proton exchange study of the hexaaqua aluminate(III) system a bimolecular process, similar to that proposed for the systems in this study, for the exchange between the [Al(OH2)6]3+ and [Al(OH2)5(OH)]2+ (64) complexes was postulated. 

Reaction (I) is a bimolecular reaction involving a protonic acid on the olefin. The proton attacks the monomer and adds to a carbon atom that has the maximum electron density. 

In view of the fact that proton transfer to monomer is the most general and effective alternative to propagation in chemically initiated bimolecular polymerizations, it seems sensible to include here the reactions (5.V). For m < mc we need to include the normal bimolecular process,... 

Intramolecular general base catalysed reactions (Section II, Tables E-G) present less difficulty. A classification similar to that of Table I is used, but since the electrophilic centre of interest is always a proton substantial differences between different general bases are not expected. This section (unlike Section I, which contains exclusively unimolecular reactions) contains mostly bimolecular reactions (e.g. the hydrolysis of aspirin [4]). Where these are hydrolysis reactions, calculation of the EM still involves comparison of a first order with a second order rate constant, because the order with respect to solvent is not measurable. The intermolecular processes involved are in fact termolecular reactions (e.g. [5]), and in those cases where solvent is not involved directly in the reaction, as in the general base catalysed aminolysis of esters, the calculation of the EM requires the comparison of second and third order rate constants. 

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