: The unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio. Harmonic force fields are obtained using Density Functional Theory (DFT), MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set. DFT calculations use the Local Spin Density Approximation (LSDA), BLYP, and Becke3LYP (B3LYP) density functionals. Mid-IR spectra predicted using LSDA, BLYP, and B3LYP force fields are of significantly different quality, the B3LYP force field yielding spectra in clearly superior, and overall excellent, agreement with experiment. The MP2 force field yields spectra in slightly worse agreement with experiment than the B3LYP force field. The SCF force field yields spectra in poor agreement with experiment.The basis set dependence of B3LYP force fields is also explored: the 6-31G* and TZ2P basis sets give very similar results while the 3-21G basis set yields spectra in substantially worse agreements with experiment. jg

Ab initio calculation of vibrational absorption and circular dichroism spectra using density functional force fields

The selective oxidation of C-H bonds and the use of O(2) as a stoichiometric oxidant represent two prominent challenges in organic chemistry. Copper(II) is a versatile oxidant, capable of promoting a wide range of oxidative coupling reactions initiated by single-electron transfer (SET) from electron-rich organic molecules. Many of these reactions can be rendered catalytic in Cu by employing molecular oxygen as a stoichiometric oxidant to regenerate the active copper(II) catalyst. Meanwhile, numerous other recently reported Cu-catalyzed C-H oxidation reactions feature substrates that are electron-deficient or appear unlikely to undergo single-electron transfer to copper(II). In some of these cases, evidence has been obtained for the involvement of organocopper(III) intermediates in the reaction mechanism. Organometallic C-H oxidation reactions of this type represent important new opportunities for the field of Cu-catalyzed aerobic oxidations.

Copper-Catalyzed Aerobic Oxidative C ? H Functionalizations: Trends and Mechanistic Insights

RECEIVED for review February 21, 1978. Accepted June 19, 1978. NMR spectra since two distinct peaks (6 -3.38, 3.78 ppm) caused by these protons are observed in CDCA vs. only one peak (6 -3.45 ppm) caused by the same protons in UDCA. T h e fingerprint region of the spectrum (6 1-2.5 ppm) and the relative position of the CIS methyl peak with respect to tha t of the doublet caused by the Cpl methyl group provide additional confirmation of the identity of the particular epimer. Accurate quantitative results are obtained from careful integration of the C3 and C7 methine proton peaks. The specific method of identification and quantitation described in this report provides an efficient alternative to the rather nonspecific identification and assay procedures by conventional techniques, some of which involve making derivatives of the bile acid epimers. This paper, which is the first publication of its kind dealing with the quantitation of

Isotope-ratio-monitoring gas chromatography-mass spectrometry

The importance of the selective activation of alkanes for science and technology in the forthcoming decades does not need to be explicitly pointed out in this thematic issue of Chemical ReViews. Instead, we would like to summarize the development and the state-of-art of experimental and theoretical methods for the investigation of model reactions for alkane activation in the gas phase.1 However, before doing so let us address the question, how other scientists, both in academia as well as industry, can profit from such model studies in the gas phase, usually involving very small, charged species under conditions in a mass spectrometer which are very far from real catalysis. To this end, we refer to the synthesis of HCN as a reasonably simple example of how large-scale technical processes can be investigated in microscopic models. † In memoriam of Dr. Andreas Fiedler. * To whom correspondence should be addressed. E-mail: detlef.schroeder@ uochb.cas.cz, E-mail: roithova@natur.cuni.cz. ‡ Charles University in Prague. § Academy of Sciences of the Czech Republic. Jana Roithová (right), Ph.D., leads a group on the topic of reaction mechanisms at the Faculty of Science at the Charles University in Prague. Her research is based on the synergy of gas-phase experiments and theoretical calculations. She received her Ph.D. degree in the group of Prof. Zdenek Herman (J. Heyrovsky Institute of Physical Chemistry, Prague) on the topic of reactivity of small molecular dications in 2003. Since then she has made key contributions to superelectrophilic chemistry in the gas phase, with particular attention toward the activation of nonreactive substrates such as rare gases, nitrogen, and methane. Recently, she concentrates her research on the properties of redox-active molecules, their interactions with transition metals, and mechanisms of organometallic reactions. She is author of more than 80 papers and received, among others, a “L’Oréal for Women in Science” stipend and the Hlavka prize.

Selective activation of alkanes by gas-phase metal ions.

Die selektive Oxidation von C-H-Bindungen und der Einsatz von O2 als stochiometrisches Oxidationsmittel stellen zwei wesentliche Herausforderungen in der organischen Chemie dar. Kupfer(II) ist ein vielseitiges Oxidationsmittel fur verschiedene oxidative Kupplungen, die durch Einelektronen-Transfer (SET) von elektronenreichen organischen Molekulen ausgelost werden. Viele dieser Reaktionen konnen mit Kupfer katalytisch durchgefuhrt werden, wenn molekularer Sauerstoff als Oxidationsmittel eingesetzt wird, um den aktiven Kupfer(II)-Katalysator zu regenerieren. Daneben wurden auch zahlreiche neue Cu-katalysierte C-H-Oxidationen mit elektronenarmen Substraten beschrieben, von denen ein SET zum Kupfer(II) unwahrscheinlich scheint. In einigen dieser Falle konnte die Beteiligung von Organokupfer(III)-Intermediaten im Reaktionsmechanismus nachgewiesen werden. Metallorganische C-H-Oxidationen dieser Art eroffnen neue bedeutende Moglichkeiten fur das Gebiet der Cu-katalysierten aeroben Oxidationen.

Kupferkatalysierte aerobe oxidative C‐H‐Funktionalisierungen: Trends und Erkenntnisse zum Mechanismus

The mechanisms of oxidative N-dealkylation of amines by heme enzymes including peroxidases and cytochromes P450 and by functional models for the active Compound I species have long been studied. A debated issue has concerned in particular the character of the primary step initiating the oxidation sequence, either a hydrogen atom transfer (HAT) or an electron transfer (ET) event, facing problems such as the possible contribution of multiple oxidants and complex environmental effects. In the present study, an oxo iron(IV) porphyrin radical cation intermediate 1, [(TPFPP)*+ Fe(IV)=O]+ (TPFPP = meso-tetrakis (pentafluorophenyl)porphinato dianion), functional model of Compound I, has been produced as a bare species. The gas-phase reaction with amines (A) studied by ESI-FT-ICR mass spectrometry has revealed for the first time the elementary steps and the ionic intermediates involved in the oxidative activation. Ionic products are formed involving ET (A*+, the amine radical cation), formal hydride transfer (HT) from the amine ([A(-H)]+, an iminium ion), and oxygen atom transfer (OAT) to the amine (A(O), likely a carbinolamine product), whereas an ionic product involving a net initial HAT event is never observed. The reaction appears to be initiated by an ET event for the majority of the tested amines which included tertiary aliphatic and aromatic amines as well as a cyclic and a secondary amine. For a series of N,N-dimethylanilines the reaction efficiency for the ET activated pathways was found to correlate with the ionization energy of the amine. A stepwise pathway accounts for the C-H bond activation resulting in the formal HT product, namely a primary ET process forming A*+, which is deprotonated at the alpha-C-H bond forming an N-methyl-N-arylaminomethyl radical, A(-H)*, readily oxidized to the iminium ion, [A(-H)]+. The kinetic isotope effect (KIE) for proton transfer (PT) increases as the acidity of the amine radical cation increases and the PT reaction to the base, the ferryl group of (TPFPP)Fe(IV)=O, approaches thermoneutrality. The ET reaction displayed by 1 with gaseous N,N-dimethylaniline finds a counterpart in the ET reactivity of FeO+, reportedly a potent oxidant in the gas phase, and with the barrierless ET process for a model (P)*+ Fe(IV)=O species (where P is the porphine dianion) as found by theoretical calculations. Finally, the remarkable OAT reactivity of 1 with C6F5N(CH3)2 may hint to a mechanism along a route of diverse spin multiplicity.

Probing the Compound I-like reactivity of a bare high-valent oxo iron porphyrin complex: the oxidation of tertiary amines.

Experimental detection of theoretically predicted N2CO.

The gas-phase reaction of SO+ with SO2, relevant to the atmospheric chemistry of Io, was investigated with mass spectrometric and computational methods. Consistent with previous reports, no net chemical change was observed at 10-8−10-7 Torr by FT-ICR spectrometry. However, formation of a transient S2O3+ adduct of OSOSO connectivity, a, was suggested by the fast (k = 6.0 ± 1.5 × 10-10 cm-3 s-1 molec-1) 34SO+/32SO2 isotope exchange. The adduct was directly observed in SO2/CI experiments, and structurally probed by MIKE and CAD spectrometry, the results of which are also consistent with connectivity a. Computational results at the B3LYP/6-311+G(2d) level of theory, complemented by single-point CCSD(T) calculations, confirmed that a planar S2O3+ ion of connectivity a is more stable at 298 K than the isomer b of connectivity OSSO2 by 23.4 kcal mol-1 at the CCSD(T) level of theory. NR spectrometry of S2O3+ allowed detection of a hitherto unknown sulfur oxide, S2O3, also of OSOSO connectivity, characterized as a...

A New Sulfur Oxide, OSOSO, and Its Cation, Likely Present in the Io's Atmosphere: Detection and Characterization by Mass Spectrometric and Theoretical Methods

A technique is described that allows the continuous elemental analysis and radiometric analysis of C14-labeled compounds separated by gas chromatography. The substances emerging from the column are converted into CO 2 and H 2, which are separated on an auxiliary column. From the ratio of the areas of the H/sub 2/and CO 2 peaks, the H: C ratio in each substance is deduced. The activity of the CO 2 peak is assayed by a 100-ml flow ionization chamber or a 100-ml internal flow proportional counter, depending on the specific activity of the sample. The method may be employed to determine the total activity in a given compound and its specific activity in one operation. Because of the separation of the R and C contained in each compound, the method shows considerable promise for simultaneous C14 and H3 assay in doubly labeled molecules.

Continuous Elemental Analysis of Gas Chromatographic Effluents. Application to the Analysis of Labeled Compounds.

F2•+ ions have been generated in the external ion source of a FT-ICR mass spectrometer, and their reactivity with a choice of neutrals, ranging from noble gases to polyatomic molecules, has been investigated. With the exception of He and Ne, all neutrals react with F2•+ at the collision controlled limit, yielding predominantly electron transfer and fragmentation products. Noteworthy, a formal F+ transfer process takes place from the reaction of F2•+ with Ar, among the noble gases, and with CO and N2, among diatomic molecules. The unimolecular and bimolecular reactivity of F2H+, obtained from the F2•+ reaction with H2, allowed the proton affinity of elemental fluorine (PA = 79 ± 5 kcal mol-1) to be experimentally derived.

Romano Cipollini

Papers

Probing the Compound I-like reactivity of a bare high-valent oxo iron porphyrin complex: the oxidation of tertiary amines.

Experimental detection of theoretically predicted N2CO.

A New Sulfur Oxide, OSOSO, and Its Cation, Likely Present in the Io's Atmosphere: Detection and Characterization by Mass Spectrometric and Theoretical Methods

Continuous Elemental Analysis of Gas Chromatographic Effluents. Application to the Analysis of Labeled Compounds.

Positive ion chemistry of elemental fluorine