The recent accurate and precise determination of the electron affinity (EA) of the astatine atom At0 warrants a re-investigation of the estimated thermodynamic properties of At0 and astatine containing molecules as this EA was found to be much lower (by 0.4 eV) than previous estimated values. In this contribution we estimate, from available data sources, the following thermodynamic and physicochemical properties of the alkali astatides (MAt, M = Li, Na, K, Rb, Cs): their solid and gaseous heats of formation, lattice and gas-phase binding enthalpies, sublimation energies and melting temperatures. Gas-phase charge-transfer dissociation energies for the alkali astatides (the energy requirement for M+ At- ➔ M0  + At0 ) have been obtained and are compared with those for the other alkali halides. Use of Born-Haber cycles together with the new AE (At0 ) value allows the re-evaluation of ΔHf (At0 )g (=56 ± 5 kJ/mol); it is concluded that (At2 )g is a weakly bonded species (bond strength <50 kJ/mol), significantly weaker bonded than previously estimated (116 kJ/mol) and much weaker bonded than I2 (148 kJ/mol), but in agreement with the finding from theory that spin-orbit coupling considerably reduces the bond strength in At2 . The hydration enthalpy (ΔHaq ) of At- is estimated to be -230 ± 2 kJ/mol (using ΔHaq [H+ ] = -1150.1 kJ/mol), in good agreement with molecular dynamics calculations. Arguments are presented that the largest alkali halide, CsAt, like the smallest, LiF, will be only sparingly soluble in water, following the generalization from hard/soft acid/base principles that "small likes small" and "large likes large."

From the NIST website and the literature, we have collected the Ionisation Energies (IE) of 3,052 and the Proton Affinities (PA) of 1,670 compounds. For 614 of these, both the IE and PA are known; this enables a study of the relationships between these quantities for a wide variety of molecules. From the IE and PA values, the hydrogen atom affinities (HA) of molecular ions M•+ may also be assessed. The PA may be equated to the heterolytic bond energy of [MH]+ and HA to the homolytic bond energy. Plots of PA versus IE for these substances show (in agreement with earlier studies) that, for many families of molecules, the slope of the ensuing line is less negative than -1, i.e. changes in the PA are significantly less than the concomitant opposite changes in IE. At one extreme (high PA, low IE) are the metals, their oxides and hydroxides, which show a slope of close to -1, at the other extreme (low PA, high IE) are the hydrogen halides, methyl halides and noble gases, which show a slope of ca. -0.3; other molecular categories show intermediate behaviour. One consequence of a slope less negative than -1 is that the changes in ionic enthalpies of the protonated species more closely follow the changes in the enthalpies of the neutral molecules compared with changes in the ion enthalpies of the corresponding radical cations. This is consistent with findings from ab initio calculations from the literature that the incoming proton, once attached to the molecule, may retain a significant amount of its charge. These collected data allow a comparison of the thermodynamic stability of protonated molecules in terms of their homolytic or heterolytic bond cleavages. Protonated nitriles are particularly stable by virtue of the very large hydrogen atom affinities of their radical cations.

Proton affinities of a number of alkyl acetates (CH3–C(=O)–OR) and of methyl alkanoates (R–C(=O)–OCH3, R=H, alkyl) have been assembled from the literature or measured using the kinetic method. It was observed that the proton affinities for the isomeric species CH3–C(=O)–OR and R–C(=O)–OCH3 are almost identical, an unexpected result as the charge in these protonated ester molecules is largely at the keto carbon atom and so this site should be more sensitive to alkyl substitution. Analysis of the data, including those from lone pair ionisation and core-electron ionisation experiments available from the literature, indicate that after protonation, extensive charge relaxation (or polarisation) takes place (as is also the case, according to the literature, after core-electron ionisation). By contrast, after lone pair ionisation, which results in radical cations, such relaxation processes are relatively less extensive. As a consequence, changes in ion enthalpies of these protonated molecules follow more closely the changes in neutral enthalpies, compared with changes in enthalpies of the corresponding radical cations, formed by electron detachment. Preliminary analyses of published energetic data indicate that the above finding for organic esters may well be another example of a more general phenomenon.

The basic principles of photoelectron spectroscopy are briefly summarized.

The relative affinity of the monovalent metal ions Li+, Na+, Cu+ and Ag+ towards a series of aliphatic alkyl acetates and some selected 1-alkenes (P) was examined using the kinetic method. A detailed analysis of the dissociation characteristics of a series of mixed metal-bound dimer ions of the type P1-M+-P2 and the evaluated proton affinities (PAs) of the monomers shows that the affinity of the cation towards long-chain alkyl acetates and alkenes (having a chain length ? C4) is markedly enhanced. In line with recent studies of nitriles, alcohols and methyl alkanoates, this is attributed to a bidentate interaction of the metal ion with the functional group or double bond and the aliphatic chain. In particular, the longer chain alkyl acetates, methyl alkanoates and alcohols show a remarkably similar behaviour with respect to silver ion hydrocarbon bonding. The Ag+ adducts of the alkyl acetates dissociate by loss of CH3COOH. This reaction becomes more pronounced at longer chain lengths, which points to metal ion bidentate formation in [Ag+···1-alkene] product ions having a long hydrocarbon chain. In the same vein, the heterodimers [1-hexene···Ag+···1-heptene] and [1-heptene·Ag+···1-octene] dissociate primarily into [Ag+···1-heptene] and [Ag+···1-octene] ions, respectively. Hydrocarbon bidentate formation in [Ag+···1-octene] also reveals itself by the reluctance of this ion to react with water in an ion trap, as opposed to [Ag+···1-hexene] which readily undergoes hydration.

Relative affinity measurements of monovalent metal ions (=Li+, Cu+ and Ag+) towards aliphatic amines, alcohols and methyl alkanoates (P) have been performed using the kinetic method on the dissociation of metal-bound dimer ions of the type P1–M+–P2. It was found that the cations' affinity towards long chain (≥C4 chain length) n- and s-alkylamines, n-alkanols and methyl n-alkanoates was unexpectedly enhanced. This is attributed to a bidentate interaction of the metal ion with the amine, alcohol or ester functional group and the aliphatic chain, paralleling earlier observations on metal-bound nitriles. Methyl substitution at the functional group ( s-alkylamines compared with n-alkylamines) serves to strengthen only the N M+ bond, and this can be rationalised by the larger proton affinities of s-alkylamines compared to n-alkylamines. This substitution, however, has no effect on the metal ion–hydrocarbon bond. In contrast, methyl substitution remote from the functional group, as in iso-pentylamine, does lead to strengthening of the metal ion–hydrocarbon bond. The cuprous ion affinity of hexadecylamine, C16H33NH2, was found to be as large as that for ethylenediamine (352 kJ mol−1), known to be a strong copper binding agent. It is argued that such a metal ion - hydrocarbon interaction does not occur in the metal bound dimers.

A broad, general understanding of the relationships between chemical structures and their various energies is of primary importance when assessing the validity of an energy derived from experiment or computation. This review is intended to provide guidance and advice for scientists seeking data for standard enthalpies of formation (ΔfH0) and ionisation energies (IE) for a wide variety of organic compounds and ΔfH0 values for their odd- and even-electron cations. The major reference sources are critically reviewed and methods are described for the accurate estimation of ΔfH0 of neutral compounds and correlation schemes for IE, proton affinities (PA) and ΔfH0 values for odd- and even-electron positive ions. ΔfH0 data for neutral organics are well reproduced by the additivity method and up-to-date tables of group values are provided, as well as directions for their application. Free radical ΔfH0 values are also reported. The situation for odd-electron cations (molecular ions) is not as simple, but reliable correlations exist between adiabatic ionisation energies (IEa) and molecular size, particularly for closely related species such as homologues, where IEa falls linearly with 1/n, n being the number of atoms. The same relationship obtains for PA. The ΔfH0 values for even-electron cations (ionised free radicals) also display useful correlations, chiefly based on the effects of substitution at a charge site, localised or delocalised. Here the relationship is exponential, with ΔfH0(Ion) being a linear function of ln(n). A separate brief guide, intended for users of the NIST WebBook seeking molecular ΔfH0 values and IE, is appended.

This study extends a previous publication on group additivity values (GAVs) for the elements C, H, and O, to include the elements nitrogen, sulfur, and the halogens. The present state and utility of the Benson additivity schemes for estimating the enthalpy of formation (Δ(f)H(0)) of organic compounds are again described, extending them to include more elements. Old and new GAVs for a wide variety of compounds are provided and are revised where necessary. When new terms are proposed, or old ones are significantly altered, the rationale for so doing is presented. GAV derived ring strain values for benzene and pyridine indicate that the aromatic stabilization of each is essentially the same. As before, the thermochemical consequences of replacing one functional group by another are also shown, thus permitting quick shortcuts to the estimation of new Δ(f)H(0) values.

It gives me great pleasure to introduce this special issue of the European Journal of Mass Spectrometry, created to celebrate the achievements of Hans Terlouw. It will necessarily be a somewhat personal account, because of my long-standing friendship and productive collaboration with JKT over nearly 40 years of research into the mysteries of gas phase ion chemistry. We have shared countless, intense hours of experimental mass spectrometry that produced a very satisfying number of mini-Eureka moments. We were also extremely fortunate to be able to spend many long discussions (in person and by trans-Atlantic ‘phone call) with the late Fred Lossing whose scientific wisdom, good humour and great technical expertise with his electron monochromator, provided the quantitative energetic foundations for so many of our mass spectral observations. Hans was born in Gouda in 1945 and his University education was completed at the University of Utrecht. After his BSc degree in 1965, which inter alia produced his first publication, he obtained an MSc in 1968, working in analytical chemistry. His PhD research was directed by Professor Geo Dijkstra, culminating in his PhD in 1972 and followed by his appointment as Assistant Professor. The thesis was entitled “A new approach to the quantitative analysis of metals by electron impact ionization mass spectrometry.” Of his first nine publications (up to 1974), five concerned the trace analysis of metals by MS. His first independent research was on the pyrolysis of cannabidol and related metastable ion and isotopic labelling studies of isomeric cannabinoids. At the 1973 International MS meeting at Edinburgh University, Professor Dijkstra asked me if I would accommodate Hans in my Ottawa laboratory for a year’s visiting Fellowship. Hans came to see me shortly thereafter at University College (London) where I was on sabbatical leave and the rest, as they say, is our history. It is difficult to overstate the value of a close, non-competitive collaboration in science and the following 15 or so years were exceptionally happy and productive, each of us spending extended visits in the other’s laboratory and inter alia getting to know each others’ co-workers. I find that we have co-authored some 70 articles in books, reviews and journals. Our first joint venture in 1973/4 involved metastable ions studies, using an AEI MS902S mass spectrometer. We then believed that analysis of metastable peak shapes could provide a useful method for ion structure identification. Fortuitously we began with the C2H4O +• isomers, vinyl alcohol, acetaldehyde and oxirane, each of which is readily identified by the characteristic profiles of their metastable H• loss peaks. Johan Klaas Terlouw, Scientist

This study examines critically the present state and utility of the Benson additivity schemes for estimating the enthalpy of formation of organic compounds. Old and new group additivity values (GAV) for a wide variety of compounds containing C, H and O are described and are revised where appropriate. When new terms are proposed, or old ones significantly altered, the rationale for so doing is provided. Corrections for such items as cis-isomer effects, gauche interactions, ring strain energies, double-bond position, conjugation effects, steric hindrance in aromatic molecules, etc. are included and discussed. Also provided are the thermochemical consequences of functional group replacements, in which one group in a molecule is substituted by another, thus providing quick short cuts to estimating new ΔfH0 values. Results derived from the new additivity terms are consistent with those produced by computational chemistry methods in general use.

A brief search in Sci Finder for oxalic acid and oxalates will reward the researcher with a staggering 129,280 hits. However, the generation of alkali metal and silver anions via collision-induced dissociation of the metal oxalate anion has not been previously been reported, though Tian and coworkers recently investigated the dissociation of lithium oxalate [18]. The exothermic decomposition of alkali metal oxalate anion to carbon dioxide in the collision cell of a triple quadrupole mass spectrometer leaves no place for the electron to reside, resulting in a double electron-transfer reaction to produce an alkali metal anion. This reaction is facilitated by the negative electron affinity of carbon dioxide and, as such, the authors believe that metal oxalates are potentially unique in this respect. The observed dissociation reactions for collision with argon gas (1.7−1.8 × 10−3 mbar) for oxalic acid and various alkali metal oxalates are discussed and summarized. Silver oxalate is also included to demonstrate the propensity of this system to generate transition-metal anions, as well.

This short account outlines the sources of thermochemical data that are important for gas phase ion chemistry. It describes some of the relationships that have been identified for the empirical estimation of enthalpies among neutral molecules, free radicals, and odd and even electron ions. For neutral species, the additivity principle works well and this has been developed to cover a very wide range of structures and isomers. Ionization energies of homologous species depend inversely on molecular size, allowing estimates to be made for missing members. For ions, the effect of a group substitution (such as replacing a hydrogen atom by, e.g., a methyl or hydroxyl group) can easily be estimated, but such results are strongly dependent upon the position of the charge site, relative to that of the substitution. Special emphasis is given to the reliability of data collections and simple directions are provided as to how critically to assess and identify less-than-satisfactory values.

The CBS-QB3, CBS-APNO and Gaussian-3 model chemistries have been used to determine the ionic and neutral heats of formation and the adiabatic ionization energies (IE(a)) derived therefrom, for the ca 30 principal isomers of the C(3)H(2)O(*+) and the C(4)H(4)O(*+) families of radical cations. Theory and experiment are in excellent agreement for those molecules whose experimental IE(a) has been accurately measured. In contrast, large deviations from the computed values were found for a great many ionic heats of formation reported in the literature. These deviations largely arise from the uncertainty in the heat of formation of the corresponding neutral species for which often only a rough estimate is available. A useful by-product of this study is that it permits the evaluation of new Benson-type group additivity (GA) terms appropriate for highly unsaturated oxygen containing molecules. Several new GA terms are proposed but it is also argued that a single GA term for the ketene function cannot be defined.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Perhaps the greatest influence that isotopic labelling experiments have had on organic mass spectrometry is that reaction mechanisms originally borrowed from the chemistry of neutral counterparts have proved to be inadequate for explaining the results. It was therefore necessary to devise completely new types of fragmentation mechanisms and unconventional structures for organic gas-phase cations. In most cases the labelling technique allows one to discover the positions at which the label atoms are found in both the charged and neutral products of an ion's dissociation. These experimental results are often difficult to rationalize by any simple mechanism, but they nearly always indicate how chemical computations should be directed in order for the latter to be able to provide a better mechanistic understanding. This short article describes some significant studies involving D and 18-O labelling that well support the above assertions, using as examples the behaviour of some quite simple organic molecules. Copyright (c) 2007 John Wiley & Sons, Ltd.

This paper describes, with examples, a critical assessment of thermochemical data for some small molecules and free radicals. The available heats of formation, Delta H-f degrees (all 298 K values). for simple alkyl hydroperoxides and di-alkyl peroxides were compared and new data are provided. The Delta H-f degrees values, all +/- 5 kJ/mol, are: CH3OOH, -135; CH3CH2OOH, -168; n-C3H7OOH, -189; S-C3H7OOH, -205; t-C4H9OOH, -240; CH3OOCH3, -132; CH3CH2OOCH3, -165; C2H5OOC2H5, -198; n-C(3)H(7)OOn-C3H7, -240; S-C3H7OOs-C3H7, -272; t-C(4)H(9)OOt-C4H9, -342. These are consistent with established O-O bond dissociation energies and with additivity considerations. Delta H-f degrees values for the corresponding alkoxy radicals are also addressed.A similar survey was applied to the homologous n-alkyl aldehydes, C2 to C8, for which recommended Delta H-f degrees values, all +/- 1.5 kJ/mol, are: -166.5, - 189, -207.5, -227, -248, -268 and -289, respectively. Particular attention was given to Delta H-f degrees(CH3CO degrees) = -10.3 +/- 1.8 kJ/mol. The current NIST WebBook datum, Delta H-f degrees(CS) = 280.3 kJ/mol, is arguably the best value, being consistent with related thermochemical data. Finally the Delta H-f degrees values for the allylic free radicals *CH2CHCH2, 174 3 kJ/mol, CH2CHCH*(OH), 4.5 +/- 4 kJ/mol, and (CH2CH)(2)*(OH), 37 +/- 4 kJ/mol, derived from experimental data and results of computational chemistry are described, together with some related homolytic bond strengths. (C) 2007 Elsevier B.V. All rights reserved.

Assigning Structures to Ions in Mass Spectrometry describes the tools currently available for determining gas-phase ion structures. It surveys current experimental methods for ion production and separation as well as those designed to reveal qualitative and quantitative aspects of gas-phase ions. It also examines how and when to apply computational chemistry and theoretical calculations. Selected case studies illustrate specific challenges associated with ion structure assignment and thermochemical problems. Bringing together key results collected over the past four decades, the book contains the data for describing or identifying ions containing C alone and C with H, O, N, S, P, halogens, and small organic cations.

The gas-phase reactions of the ion [CH3CHO/H2O](+.) have been investigated by mass spectrometry. The metastable ion (MI) mass spectrum reveals that this ion-molecule complex decomposes spontaneously by the losses of H2O, CO, and (CH3)-C-.. The structures of stable complexes and transition states involved in the potential energy surface (PES) have been studied by the G3//B3-LYP/6-31+G(d) computational method. Hydrogen- bridged water complexes have been found to be the major products of the losses of CO and (CH3)-C-.. The CO loss produces the [(CH3)-C-.center dot center dot center dot H3O+] ion and involves a "backside displacement" mechanism. The products corresponding to (CH3)-C-. loss have been assigned by theory to be [OC center dot center dot center dot H3O+] and [CO center dot center dot center dot H3O+], and their 298 K enthalpy values, calculated at the G3 level of theory, are Delta H-f-[OC center dot center dot center dot H3O+] = 420 kJ/mol and Delta H-f-[CO center dot center dot center dot H3O+] = 448 kJ/mol. The PES describing the interconversions among water-solvated CH3CHO+., CH3COH+., and CH2CHOH+. have been shown to involve proton-transport catalysis (PTC), catalyzed 1,2 H-transfer, and an uncatalyzed H-atom transfer mechanism, respectively.

The fragmentation of the 2,3-pentanedione radical cation gives rise to an unexpected composite metastable ion peak, m/z 72, resulting from the isobaric losses of CO and C2H4. These two fragmentation channels are energetically competitive (i.e., the transition states have similar energies). The two processes yield [CH3C(O)CH2CH3]+ and [CH3C(OH)CO]+, respectively. The latter new ion, which is produced by a McLafferty rearrangement, has ΔfH°=604kJ/mol, obtained from G3 calculations. The four competing processes for metastable [CH3COCOCH2CH3]+, the (intense) losses of CH3CO, CH3CH2CO and the weak losses of C2H4 and CO and their transition states were placed on a potential energy surface computed at the G3 level of theory. The homologous ionized diketone 2,3-butanedione also displays the decarbonylation channel and 3,4-hexanedione loses CO and C2H4.