DFT based insights into reactivity descriptors of encapsulated B<Subscript>24</Subscript>N<Subscript>24</Subscript> nanocages

The purpose of this study is to probe the DFT based chemical reactivity parameter, electrophilicity index as a possible molecular engineering of endohedral BN-nanocages. The structure and electronic properties of endohedral boron nitride nanocages have been investigated as a function of alkali atom inside the nanocage using density functional theory. We have calculated and analyzed basic characteristic related to the reactive behavior, such as HOMO–LUMO band gap, chemical hardness, chemical potential, vertical electron affinity, and vertical ionization potential, as well as the global electrophilicity index, ω(I, A) of the encapsulated B₂₄N₂₄ nanocages. We also investigated the MQZVP basis set effect on total electronic energy of the clusters.     

Effect of protonation exothermicity on the chemical ionization mass spectra of some alkylbenzenes

The H₂, N₂/H₂, CO₂/H₂, N₂O/H₂, CO/H₂ and CH₄ chemical ionization mass spectra of thirteen C₈ to C₁₁ alkylbenzenes are reported. Characteristic hydride and alkide ion abstraction reactions are observed with all reagent gases. The major fragmentation reactions of [MH]⁺ are olefin elimination to form a protonated arene and arene elimination to form an alkyl ion. From the effect of structure and protonation exothermicity it is concluded that rearrangement of primary alkyl groups to the more stable secondary or tertiary structure occurs prior to alkyl ion formation. A detailed fragmentation mechanism for protonated arenes is proposed. The ‘effective’ proton affinity of the methane-derived reagent system is estimated to be ～556 kJ mol^?1.     

Fluorescence of dissociating fragments from supersonic jet-electron collisions

Supersonically cooled jets of nitrogen, methane, ethane, cyclopropane, and azomethane are crossed with collimated streams of electrons. The CH (B²Σ^? → X²Π) spectra resulting from the electron-induced dissociation of CH₄, C₂H₆, and CH₂)₃ can be fit with rotation temperatures between 4000 and 6000 K for an electron energy of 100 eV. Flourescence spectra of N₂⁺ (B²Σ_w⁺ → X²Π) from the dissociative ionization of azomethane yield a rotational temperature of =8×10³ K; from ionization of molecular nitrogen the rotational temperature of B²Σ_w⁺ N₂⁺ is 45 K. Mechanisms for these various processes are discussed.     

Dihydrogen Catalysis of the Reversible Formation and Cleavage of CH and NH Bonds of Aminopyridinate Ligands Bound to (η5‐C5Me5)IrIII

This study focuses on a series of cationic complexes of iridium that contain aminopyridinate (Ap) ligands bound to an (η⁵‐C₅Me₅)Ir^III fragment. The new complexes have the chemical composition [Ir(Ap)(η⁵‐C₅Me₅)]⁺, exist in the form of two isomers ( 1⁺ and 2⁺ ) and were isolated as salts of the BAr_F^? anion (BAr_F=B[3,5‐(CF₃)₂C₆H₃]₄). Four Ap ligands that differ in the nature of their bulky aryl substituents at the amido nitrogen atom and pyridinic ring were employed. In the presence of H₂, the electrophilicity of the Ir^III centre of these complexes allows for a reversible prototropic rearrangement that changes the nature and coordination mode of the aminopyridinate ligand between the well‐known κ²‐N,N′‐bidentate binding in 1⁺ and the unprecedented κ‐N,η³‐pseudo‐allyl‐coordination mode in isomers 2⁺ through activation of a benzylic C?H bond and formal proton transfer to the amido nitrogen atom. Experimental and computational studies evidence that the overall rearrangement, which entails reversible formation and cleavage of H?H, C?H and N?H bonds, is catalysed by dihydrogen under homogeneous conditions.     

The Influence of Small Hydrogen Admixtures up to 5?% to a Low Pressure Nonuniform Microwave Discharge in Nitrogen

We present the results of spectroscopic and 2D modeling study of the influence of hydrogen addition to non-uniform nitrogen plasma of electrode microwave discharge. The axial intensity distributions of the H_?? line and N₂ (2⁺: C³??_u????B³??_g, 1⁺: B³??_g????A³?? _u ⁺ ) and N₂ ⁺ (1^?: B²?? _u ⁺ ???X²?? _g ⁺ ) molecular bands are recorded for different incident microwave power input and hydrogen content. The corona model is used to determine electric field strength in nitrogen discharge from the intensity ratio of 2⁺ and 1^? system of nitrogen bands. By means of 2D modeling spatial distributions of nitrogen molecules in C³??_u state, microwave field strength, electron density, concentrations of N₂ ⁺, N₄ ⁺ are determined in nitrogen and in nitrogen?Chydrogen mixtures. The concentration of N₂H⁺ ions in nitrogen?Chydrogen mixtures is determined also. The general conclusion of 2D modeling is in agreement with experimental results and shows that the influence of hydrogen addition to discharge is related to the fast conversion reactions of nitrogen ions (N₂ ⁺, N₄ ⁺) to N₂H⁺ ion. These ion conversions lead to the change of ion plasma components transport properties, to the modification of microwave field strength in plasma, and consequently, to the alternation of all plasma parameters.     

Adduct ion formation by metal complexes under methane negative chemical ionization conditions

Negative chemical ionization mass spectrometry is used as a probe to examine reactions between hydrocarbon radicals and metal complexes in the gas phase. The methane negative chemical ionization mass spectra of 27 complexes of cobalt(II ), nickel(II ) and copper(II ) in the presence of O₄, O₂N₂ and N₄ donor atom sets are characterized by two dominant series of adduct ions of the form [M + C_nH_2n]^? and [M + C_nH_2n+1]^? at m/z values above the molecular ion, [M]^?. Insertion of the CH radical into the ligand followed by radical/radical recombination and electron capture is proposed as the major mechanism leading to the formation of [M + C_nH_2n]^? adduct ions. A second pathway involves ligand substitution by C_nH_2n+1 radicals concomitant with H elimination and electron capture. Oxidative addition at the metal followed by ionization is suggested as the principal pathway for the formation of [M + C_nH_2n+1]^? adduct ions.     

Theoretical prediction of ionization potential,electron affinity,and electronic spectrum of the S2N radical

Ab initio MRD –CI calculations using a basis set of near Hartree–Fock quality have been carried out to calculate the ground-state electronic structure of S₂N⁺, S₂N, and S₂N^? and the ionization potential, electron affinity, and vertical electronic spectrum of S₂N. At the highest level of theory (estimated full CI or FCI ), S₂N⁺ is predicted to have a linear structure with r(N? S) = 1.51 Å. For S₂N and S₂N^?, the minimum in energy at the FCI level corresponds to a quasi-linear [with a barrier height to linearity of about 2.0 kcal mol^?1, ] and a bent structure , respectively. The adiabatic/vertical ionization potential and electron affinity of S₂N are predicted to be 7.26/7.82 and 1.60/0.79 eV, respectively. Of the several electronic transitions in S₂N considered, the ones with the excitation energy of 1.87 eV (X² A₁ → ²B₂) and 2.87 eV (X²A₁ → ²B₂) are somewhat intense (? = 0.005 and 0.002) and likely to be observed.     

The elimination of metal(I) hydride in the mass spectra of some metal(II) compounds

Metal(I) hydrides are eliminated as neutral species in the electron impact ionization mass spectra of copper(II) and palladium(II) complexes of ethylene-N,N′-3-benzoylprop-2-en-2-amine. Deuterium labelling shows that the hydrogen atom of the metal(I) hydride is derived predominantly from the ethylene bridge both for ion source reactions and for metastable ion transitions. Evidence supporting the proposed rationalization for elimination of metal(I) hydride is provided by the observation of an analogous reaction in the mass spectrum of (ethylene-N,N′-salicylaldiminato)copper(II). The mass spectrum of ethylene-d₄-N,N′-3-benzoylprop-2-en-2-amine shows an unusual rearrangement to give [C₇H₅D₂]⁺ ions involving a formal phenyl-to-methylene transfer.     

Interaction of the Benzenium Ion with Inert Ligands: IR Spectra of C6H7+?Ln Cluster Cations (L=Ar,N2, CH4, H2O)

IR photodissociation spectra of mass‐selected clusters composed of protonated benzene (C₆H₇⁺) and several ligands L are analyzed in the range of the C? H stretch fundamentals. The investigated systems include C₆H₇⁺? Ar, C₆H₇⁺? (N₂)_n (n=1–4), C₆H₇⁺? (CH₄)_n (n=1–4), and C₆H₇⁺? H₂O. The complexes are produced in a supersonic plasma expansion using chemical ionization. The IR spectra display absorptions near 2800 and 3100 cm^?1, which are attributed to the aliphatic and aromatic C? H stretch vibrations, respectively, of the benzenium ion, that is, the σ complex of C₆H₇⁺. The C₆H₇⁺? (CH₄)_n clusters show additional C? H stretch bands of the CH₄ ligands. Both the frequencies and the relative intensities of the C₆H₇⁺ absorptions are nearly independent of the choice and number of ligands, suggesting that the benzenium ion in the detected C₆H₇⁺? L_n clusters is only weakly perturbed by the microsolvation process. Analysis of photofragmentation branching ratios yield estimated ligand binding energies of the order of 800 and 950 cm^?1 (≈9.5 and 11.5 kJ mol^?1) for N₂ and CH₄, respectively. The interpretation of the experimental data is supported by ab initio calculations for C₆H₇⁺? Ar and C₆H₇⁺? N₂ at the MP 2/6‐311 G(2df,2pd) level. Both the calculations and the spectra are consistent with weak intermolecular π bonds of Ar and N₂ to the C₆H₇⁺ ring. The astrophysical implications of the deduced IR spectrum of C₆H₇⁺ are briefly discussed.     

A theoretical study of protonation of triatomic silicon–carbon compounds

Ab initio molecular orbital methods are employed to study the low-lying states of C₃H⁺, SiC₂H⁺, Si₂CH⁺, and Si₃H⁺. Special attention is paid to a comparative study between C₃H⁺ and Si₃H⁺. In both cases a ³B₂ state is found to lie the lowest at the HF level, although inclusion of correlation effects favor a linear structure (¹Σ⁺ state) for C₃H⁺, which lies 25 kcal/mol below the ³B₂ state at the MP 4 level, and a bent structure (¹A′ state) for Si₃H⁺, which lies just 2 kcal/mol below the ³B₂ state. The proton affinities of C₃, SiC₂, Si₂C, and Si₃ are estimated at different levels of theory. Both protonation at carbon and silicon atoms are considered for SiC₂ and Si₂C. It is found that C₃ comparatively has a low proton affinity. On the other hand, Si₃ has a relatively high proton affinity compared with the protonation at silicon atom for both SiC₂ and Si₂C. These results are discussed on the basis of electronic structure arguments.     

DR. Maurits Dekker: A Pioneer in Scientific Publishing

Abstract

Organic salts as initiators [A? ⁺B^?: Ph?₃C⁺ClO^? ₄, Ph?₃C⁺SbCl^? ₆, (?)Sp? ⁺ClO^? ₄, and (?)(Sp)?₂ ³⁺(ClO₄)^? ₃] and catalysts [A ⁺B?^?: (+)CSA?; A? ⁺B?^?: ph?₃C⁺(+)CSA?^? and (?)Sp?⁺(+)CSA?^?] are prepared and characterized by the dissociation constant (K _d), fraction of free ions (α), and specific rotation. The asymmetrically stereoselective induction of the initiators and catalysts in the polymerization of N-vinylcarbazole is in the order A? ⁺B?^? > A ⁺B?^? > A? ⁺B^?. The specific rotations of the poly(N-vinylcarbazole) (PVCZ)s obtained are generally in this order.     

Reactions of (Nonafluorocyclohexen-1-yl)xenon(II) Hexafluoroarsenate with Halide Anions

The products of the reaction between the electrophilic alkenylxenonium cation [1-Xe⁺–C₆F₉] and the halide anions I^?, Br^?, Cl^? and F^? depend on the hardness of the halide anion. With the soft halides I^? and Br^? Xe(II) is formally displaced by halogen as well in basic MeCN as in superacidic (AHF¹), whereas with hard fluoride and chloride no reaction takes place in AHF. In MeCN F^? initiates the formation of alkenyl radicals, which abstract hydrogen from the solvent, whereas Cl^? exhibits borderline character: RH and RCl formation. Possible reaction paths are discussed. The reactivity of the arylxenonium cation [C₆F₅Xe]⁺ in AHF toward halide ions is reported and the relative electrophilicity of the cations [C₆F₅Xe]⁺ and [1-Xe⁺–C₆F₉] is determined by the competitive reaction with Cl^?. In addition the synthesis of cyclohexene 1-CF₃–C₆F₉ from C₆F₅CF₃ and XeF₂ is performed and its electrophilicity is compared with that of the aromatic compound C₆F₅CF₃.     

Chemical ionization desorption mass spectrometry of some quaternary ammonium salts

The ammonia chemical ionization desorption spectra of N,N-dimethyl quaternary ammonium iodides in addition to high protonated molecular ion [M + H]⁺ intensity, show signals for an ion radical composed of N-methyl abstracted salt cation and ammonia [C + NH₃? CH₃]^+˙. These ions corresponding to the cation +2 show increased importance in the chemical ionization mode, using the same reagent gas. The technique of chemical ionization desorption appears suitable for the analysis of salts, and thus for the determination of the molecular weight of both anion and cation.     

[M + 11]+˙ and [M + 11]−˙ ions in the nitrogen positive and negative ion chemical ionization mass spectra of aromatic amines

The N₂ negative ion chemical ionization (NICI) mass spectra of aniline, aminonaphthalenes, aminobiphenyls and aminoanthracenes show an unexpected addition appearing at [M + 11]^?˙. This addition is also observed in the N₂ positive chemical ionization (PCI) mass spectra. An ion at [M – 15]^? is found in the NICI spectra of aminoaromatics such as aniline, 1- and 2-aminonaphthalene and 1- and 2-aminoanthracene. Ion formation was studied using labeled reagents, variation of ion source pressure and temperature and examination of ion chromatograms. These experiments indicate that the [M + 11]^?˙, [M – 15]^?˙ and [M + 11]^+˙ ions result from the ionization of analytes altered by surface-assisted reactions. Experiments with ¹⁵N₂, [¹⁵N] aniline, [2,3,4,5,6-²H₅] aniline and [¹³C₆] aniline show that the [M + 11]^?˙ ion corresponds to [M + N – 3H]^?˙. The added nitrogen originates from the N₂ buffer gas and the addition occurs with loss of one ring and two amino group hydrogens. Fragmentation patterns in the N₂ PCI mass spectrum of aniline suggest that the neutral product of the surface-assisted reaction is 1,4-dicyanobuta-1,3-diene. Experiments with diamino-substituted aromatics show analogous reactions resulting in the formation of [M – 4H]^?˙ ions for aromatics with ortho-amino groups. Experiments with methylsubstituted aminoaromatics indicate that unsubstituted sites ortho to the amino group facilitate nitrogen addition, and that methyl groups provide additional sites for nitrogen addition.     

A density functional study of Fe(SINGLE BOND)N2, Fe(SINGLE BOND)N+2, and Fe(SINGLE BOND)N−2

The interaction of an iron atom with molecular nitrogen was studied using density functional theory. Calculations were of the all-electron type and both conventional local and gradient-dependent models were used. A ground state of linear structure was found for Fe(SINGLE BOND)N₂, with 2S + 1 = 3, whereas the triangular Fe(SINGLE BOND)N₂ geometry, of C_2v symmetry, was located 2.1 kcal/mol higher in energy, at least for the gradient-dependent model. The reversed order was found using the conventional local approximation. In Fe(SINGLE BOND)N₂, the N(SINGLE BOND)N bond is strongly perturbed by the iron atom: It has a bond order of 2.4, a vibrational frequency of 1886 cm⁻¹, and an equilibrium bond length of 1.16 Å: These values are 3.0, 2359 cm⁻¹, and 1.095 Å, respectively, for the free N₂ molecule. With the gradient-dependent model and corrections for nonsphericity of the Fe atom, a very small binding energy, 8.8 kcal/mol, was calculated for Fe(SINGLE BOND)N₂. Quartet ground states were found for both Fe(SINGLE BOND)N⁺₂ and Fe(SINGLE BOND)N⁻₂. The adiabatic ionization potential, electron affinity, and electronegativity were also computed; the predicted values are 7.2, 1.22, and 4.2 eV, respectively. © 1997 John Wiley & Sons, Inc.     

Quantification of Ion‐Pairing Effects on the Nucleophilic Reactivities of Benzoyl‐ and Phenyl‐Substituted Carbanions in Dimethylsulfoxide

Second‐order rate constants for the reactions of acceptor‐substituted phenacyl (PhCO?CH^??Acc) and benzyl anions (Ph?CH^??Acc) with diarylcarbenium ions and quinone methides (reference electrophiles) have been determined in dimethylsulfoxide (DMSO) solution at 20 °C. By studying the kinetics in the presence of variable concentrations of potassium, sodium and lithium salts (up to 10^?2 mol L^?1), the influence of ion‐pairing on the reaction rates was examined. As the concentration of K⁺ did not have any influence on the rate constants at carbanion concentrations in the range of 10^?4–10^?3 mol L^?1, the acquired rate constants could be assigned to the reactivities of the free carbanions. The counter ion effects increase, however, in the series K⁺<Na⁺<Li⁺, and the sensitivity of the carbanion reactivities toward variation of the counter ion strongly depends on the structure of the carbanions. The reactivity parameters N and s_N of the free carbanions were derived from the linear plots of log k₂ against the electrophilicity parameters E of the reference electrophiles, according to the linear‐free energy relationship log k₂(20 °C)=s_N(N+E). These reactivity parameters can be used to predict absolute rate constants for the reactions of these carbanions with other electrophiles of known E parameters.     

Substitution reactions in the secondary ion mass spectrometry of N-methylpyridinium halides

Secondary ion mass spectra of N-methylpyridinium halides (C⁺X^?, where C⁺ is a pyridinium cation and X^? is a halogen anion) exhibit the C⁺ ions, a series of cluster ions ((C⁺)_n(X^?)_n–1) and, furthermore, remarkable [CX – R]⁺ ions (R = H or Me). The mechanism of the formation of [CX – R]⁺ ions was investigated by the use of deuterated compounds and B/E and B²/E constant linked-scan measurements. A possible explanation is proposed in which the ions are produced through substitution reactions between species constituting the C₂X⁺ cluster ions in the gas phase.     

The antiestrogen [2‐(4‐benzyl­phenoxy)­ethyl]­diethyl­ammonium chloride

The crystal structure of the title compound, C₁₉H₂₆NO⁺·Cl^? (common name: N,N‐diethyl‐2‐[(4‐phenyl­methyl)phenoxy]‐ethan­amine hydro­chloride), contains one mol­ecule in the asymmetric unit. The planes through the two phenyl rings are roughly perpendicular. Protonation occurs at the N atom, to which the Cl^? ion is linked via an N—H?Cl hydrogen bond. The mol­ecule adopts an eclipsed rather than extended conformation.     

Characterization of N‐Boc/Fmoc/Z‐N′‐formyl‐gem‐diaminoalkyl derivatives using electrospray ionization multi‐stage mass spectrometry

N‐Boc/Fmoc/Z‐N′‐formyl‐gem‐diaminoalkyl derivatives, intermediates particularly useful in the synthesis of partially modified retro‐inverso peptides, have been characterized by both positive and negative ion electrospray ionization (ESI) ion‐trap multi‐stage mass spectrometry (MSⁿ). The MS² collision induced dissociation (CID) spectra of the sodium adduct of the formamides derived from the corresponding N‐Fmoc/Z‐amino acids, dipeptide and tripeptide acids show the [M + Na‐NH₂CHO]⁺ ion, arising from the loss of formamide, as the base peak. Differently, the MS² CID spectra of [M + Na]⁺ ion of all the N‐Boc derivatives yield the abundant [M + Na‐C₄H₈]⁺ and [M + Na‐Boc + H]⁺ ions because of the loss of isobutylene and CO₂ from the Boc protecting function. Useful information on the type of amino acids and their sequence in the N‐protected dipeptidyl and tripeptidyl‐N′‐formamides is provided by MS² and subsequent MSⁿ experiments on the respective precursor ions. The negative ion ESI mass spectra of these oligomers show, in addition to [M‐H]^?, [M + HCOO]^? and [M + Cl]^? ions, the presence of in‐source CID fragment ions deriving from the involvement of the N‐protecting group. Furthermore, MSⁿ spectra of [M + Cl]^? ion of N‐protected dipeptide and tripeptide derivatives show characteristic fragmentations that are useful for determining the nature of the C‐terminal gem‐diamino residue. The present paper represents an initial attempt to study the ESI‐MS behavior of these important intermediates and lays the groundwork for structural‐based studies on more complex partially modified retro‐inverso peptides. Copyright © 2013 John Wiley & Sons, Ltd.     

Gas phase reactions of the ion C5H5Fe+: A kinetic study

The kinetics of gas phase reactions of the ion C₅H₅Fe⁺ with oxygen (Me₂CO, Me₂O, MeOH, iso-propanol, H₂O) and nitrogen (NH₃, NH₂Me, NHMe₂, NMe₃) donor ligands have been studied by ion trap mass spectrometry. While in the literature reactions of the ion Fe⁺, with the same ligands, the principal reaction path involves fragmentation in almost all the reactions of the ion C₅H₅Fe⁺, formation of adduct ions is the major reaction path. The reactivity of these two ions is briefly compared in the ion trap conditions. Kinetic data for the ion C₅H₅Fe⁺ indicate that the reactions show a large range of efficiency and a linear correlation is found between the log of the reaction rate constants and the ionization energy of ligands with the same donor atom.