Protonated 4-bromophenol and 4-bromoanisole produced by methane chemical ionization are found to easily be dehalogenated upon high (8 keV) or low (20-30 eV) energy collisional activation giving essentially phenol and anisole radical cations, respectively. Under similar conditions, protonated unsubstituted anisole is also readily demethylated generating the phenol ion but not cyclohexadienone ions. Other nonconventional isomers of ionized phenol are only detected by MS/MS/MS experiments performed on [M-CO] •+ ions from salicylaldehyde. (U)B3LYP/6-311++G(d,p) and CASPT2/6-31G(d,p) calculations indicate the higher stability of the phenol radical cation with respect to the other six-membered-ring isomers. The least energy demanding fragmentation, namely, the decarbonylation, is shown to involve the intermediacy of six-membered ketones, open-chain ketenes, and five-membered cyclopentadiene isomeric ions. The rate determining step corresponds to the enol-keto interconversion with an energy barrier of about 276 kJ/mol relative to the phenol ion, which is markedly smaller than that required for hydrogen atom loss, deprotonation, or CO loss from an open-chain form. This suggests a crucial role played by the solvent in the readiness of the deprotonation of phenol ions in nonpolar media. The adiabatic ionization energy of phenol is evaluated as IE a (C 6 H 5 O) ) 8.35 ( 0.2 eV (exptl: 8.49 eV), and the proton affinity of the phenoxy radical is evaluated as PA(C 6 H 5 O) ) 863 ( 10 kJ/mol (exptl: 860 kJ/mol), PA(phenol) ) 826 ( 10 kJ/mol (exptl: 818 kJ/mol), and PA(anisole) ) 848 ( 10 kJ/mol.

The translational kinetic energy release distribution (KERD) in the halogen loss reaction of the chloro-, bromo-, and iodobenzene cations has been experimentally determined in the microsecond time scale and theoretically analyzed by the maximum entropy method. The KERD is constrained by the square root of the translational energy, i.e., by the momentum gap law. This can be understood in terms of quantum-mechanical resonances controlled by a matrix element involving a localized bound state and a rapidly oscillating continuum wave function, as in the case of a vibrational predissociation process. The energy partitioning between the reaction coordinate and the set of the remaining coordinates is nearly statistical, but not quite: less translational energy is channeled into the reaction coordinate than the statistical estimate. The measured entropy deficiency leads to values of the order of 80% for the fraction of phase space sampled by the pair of fragments with respect to the statistical value. In the case of the dissociation of the chlorobenzene ion, it is necessary to take into account a second process which corresponds to the formation of the chlorine atom in the excited electronic state 2P1/2 in addition to the ground state 2P3/2. The observations are compatible with the presence of a small barrier (of the order of 0.12 eV) along the reaction path connecting the D̃ 2A1 state of C6H5Cl+ to the Cl(2P1/2)+C6H5+(X̃ 1A1) asymptote.

Well‐defined amphiphilic PCL‐b‐PDMAEMA block copolymers were successfully synthesized by a combination of ATRP and “click” chemistry following either a commutative two‐step procedure or a straightforward one‐pot process using CuBr · 3Bpy as the sole catalyst. Compared to the traditional coupling method, combining ATRP and click chemistry even in a “one‐pot” process allows the preparation of PCL‐b‐PDMAEMA diblock copolymers characterized by a narrow molecular weight distribution and quantitative conversion of azides and alkynes into triazole functions. Moreover, the amphiphilic character of these copolymers was demonstrated by surface tension measurements and critical micellization concentration was calculated.magnified image

No abstract

No abstract

An RF-only quadruple collision cell, fitted with retardation and acceleration lenses, has been installed in a field-free region of a large-scale tandem mass spectrometer. This new arrangement has allowed decelerated, mass-selected ions (ca. 5 eV kinetic energy) to react with reagent gases and reaccelerated, mass-selected products (cu. 8 keV) to be subsequently identified by collisional activation mass spectrometry. The system was tested by looking at ion/molecule reactions of cyelobutanone molecular ions, previously studied by FTICR mass spectrometry Collisional activation (CA) mass spectrometry is a well-established technique for the characterization of fast-ion beams.' Isomeric ions are usually clearly distinguished because the technique provides not only fingerprint spectra of isomers, but also direct structural information, since simple, site-specific cleavages are frequently induced. CA mass spectrometry has more recently been implemented as the powerful neutralization-reionization (NR) technique' which, due to a higher energy deposition in the ions,3 gives rise to spectra which are even more structurally significant.In some instances, however, the interpretation of CA spectra is not straightforward and a further stage of mass spectrometric analysis, i.e. an MS/MS/MS (MS3) experiment is then r e q~i r e d .~ In these experiments, collision-induced fragments are mass-selected and subjected to a further collisional activation step. It must be recognized that such experiments may just displace the initial problem and other kinds of information are therefore required. The occurrence of post-collisional isomerization of ions may also introduce ambiguities; such processes have been reported recently for some sulfur-containing organic ions.The reactivity of ions towards neutral reagents provides another method for isomer differentiation. Such reactions are most easily performed in a chemical ionization (CI) source and, if the source is installed on a sector instrument, mass-selected products can be identified by high-energy collisional activation.6 It is, however, often difficult to identify unambiguously the reaction which leads to a specific product, since different ions and neutrals are present at the same time. This difficulty can be overcome by the use of Fourier-transform ion cyclotron resonance (FTICR) methodology which allows mass-selected ions to be collisionally stabilized, to react with appropriate reagents or to be collisionally dec~mposed.~ Note, however, that fragmentation of these precursor ions takes place at low kinetic energy.Other recent instrumentation allowing inter uliu the study of ion/molecule reactions has been recently reviewed by Cooks et aL8 Among the different approaches, results obtained by these authors using a home-built pentaquadrupole instrument appear quite Authors for correspondence promi~ing.~ Again, collision-induced dissociations of the ion/molecule products are obtained in the low kinetic energy regime.We describe in this paper the modification of a large sector mass spectrom...

No abstract

No abstract