Ortho,Effects in organic molecules on electron impact: X—unusual ortho effects of the methyl group in o-picolinotoluidide

The mass spectrum of o-picolinotoluidide gives rise to three major fragments at m/z 184, m/z 169 and m/z 168, corresponding to the loss of CO from the molecular ion followed by the loss of ?H₂ and ?H₃ by independent pathways. It has been shown that the ortho methyl group and the nitrogen of the pyridine ring in the 2-position are involved in the formation of these three major fragments observed in the mass spectrum of o-picolinotoluidide. The mass spectrum of 2-(o-toluidino) pyridine, the molecular ion of which can resemble the [M? CO]⁺ ion in o-picolinotoluidide, also shows loss of CH₃ and NH₂ radicals from the molecular ions. Based on these observations coupled with the high resolution data, the mass analysed ion kinetic energy spectrometry and high voltage scans of these fragments in both the compounds, two mechanistic pathways have been proposed for the formation of these ions in o-picolinotoluidide.     

Loss of CO from the molecular ions of o-, m- and p-anisoyl fluorides,CH3OC6H4COF,with fluorine atom migration

Loss of CO from the molecular ions ([CH₃OC₆H₄COF]⁺˙) of o-, m- and p-anisoyl fluorides has been investigated by mass-analysed ion kinetic energy (MIKE) spectrometry. This reaction involves fluorine atom migration from the carbonyl group to the benzene ring. In the cases of o- and p-anisoyl fluorides, the fluorine atom migrates via a three-membered transition state to form the molecular ions ([CH₃OC₆H₄F]⁺˙) of o- and p-fluoroanisoles, respectively. On the other hand, in the case of m-anisoyl fluoride, the fluorine atom migrates from the carbonyl group to the benzene ring via a three- or four-membered transition state.     

Proportionality of intrinsic heat of transport to standard entropy of hydration for aqueous ions

Intrinsic ionic heats of transport q _o ^* (ion) and ionic heats of transport Q _o ^* (ion) have been evaluated for 53 aqueous ions at infinite dilution at 25°C using the reduction rule proposed by the authors and the limiting laws of Agar, and of Helfand and Kirkwood without electrophoretic terms. q _o ^* (ion) have been found to correlate linearly with the standard ionic entropies of hydration for the 38 ions investigated. The correlation yields three distinctive proportionality constants indicating that the ions may be divided into three distinctive groups. Although the sign of Q _o ^* (ion) is not definite, all values of q _o ^* (ion) are positive. For 17 ions Q _o ^* (ion) are in good agreement with TS _o ^* (ion). Here, S _o ^* (ion) is the absolute standard ionic entropy of transport which can be obtained from potentiometric measurements on cells. The values of S _o ^* (ion) were determined by Agar, and recently by Lin and coworkers.     

Hydrogen-carbon,carbon-carbon double rearrangement induced by proximity effects. 1–formation of methoxybenzyl ions in the electron impact mass spectra of substituted 1,1-bis(dimethoxyphenyl)methanes

The 75 eV electron impact mass spectra of 1,1-bis(dimethoxyphenyl)methanes bearing o-methoxy groups are dominated by intense peaks corresponding, at least formally, to benzyl ions [(CH₃O)₂C₆H₃CH₂]⁺ (b). They arise from ions [((CH₃O)₂C₆H₃)₂CH]⁺ (a), which are in turn formed from molecular ions by loss of an alkyl radical through benzylic cleavage. The analysis of compounds labelled with ²H or ¹³C at methoxy groups led to the determination of the mechanism. Hydrogen migration, as hydride, followed by electrophilic substitution by the methylene carbon of the phenyl methylene ether cation through a six-centred transition state is responsible for the formation of benzylic ions b.     

Synthesis and electron impact mass spectra of 3-substituted 2-acylaminoindazoles

3-Substituted-2-acylaminoindazoles 2 were prepared via oxidative cyclization of o-aminoaryl ketone acylhydrazones 1 with iodosobenzene diacetate. Their electron ionization mass spectra were recorded and in addition to the molecular ions show common fragmentation pathways corresponding to the [M-N₂]⁺, [M-NHCOX]⁺ and [M-COX]⁺ ions, with some influence on the skeletal fragmentation by different substituents.     

Fragmentation characteristics of hydroxycinnamic acids in ESI‐MSn by density functional theory

This work aims to analyze the electrospray ionization multistage mass spectrometry (ESI‐MSⁿ) fragmentation characteristics of hydroxycinnamic acids (HCAs) in negative ion mode. The geometric parameters, energies, natural bond orbitals and frontier orbitals of fragments were calculated by density functional theory (DFT) to investigate mass spectral fragmentation mechanisms. The results showed that proton transfer always occurred during fragmentation of HCAs; their quasi‐molecular ions ([M − H]⁻) existed in more than one form and were mainly with the lowest energy. The fragmentation characteristics included the followings: (1) according to the different substitution position of phenolic hydroxyl group, the ring contraction reaction by CO elimination from benzene was in an increasingly difficult order: m‐phenolic hydroxyl > p‐phenolic hydroxyl > o‐phenolic hydroxyl; and (2) ortho effect always occurred in o‐dihydroxycinnamic acids (o‐diHCAs), i.e. one phenolic hydroxyl group offered H⁺, which combined with the other one to lose H₂O. In addition, there was a nucleophilic reaction during ring contraction in diHCAs that oxygen atom attacked the carbon atom binding with the other phenolic hydroxyl to lose CO₂. The fragmentation characteristics and mechanism of HCAs could be used for analysis and identification of such compounds quickly and effectively, and as reference for structural analogues by ESI‐MS. Copyright © 2017 John Wiley & Sons, Ltd.     

Formation and stability of gaseous tolyl ions

Collisional activation mass spectra confirm that tolyl ions can be produced from a variety of CH₃C₆H₄Y compounds. High purity o-, m- and p-tolyl ions are prepared by chemical ionization of the corresponding fluorides (Y=F) as proposed by Harrison. In electron ionization of CH₃C₆H₄Y formation of the more stable tropylium and benzyl ionic isomers usually accompanies that of the o-, m- and p-tolyl ions. Isomerization of low energy [CH₃C₆H₄Y]⁺? to [Y–methylenecyclohexadiene]⁺? is proposed to account for most [benzyl]⁺ formation, while the tropylium ion appears to arise from the isomerization of tolyl ions formed with higher internal energies, [o-, m-, p-tolyl]⁺→ [benzyl]⁺→ [tropylium]⁺, consistent with Dewar's predictions from MINDO/3 calculations.     

Rearrangements in the molecular ion of o-(methyl-d3-thio)benzoic Acid: Comparison with o-methoxy-d3-benzoic acid

Hydrogen/deuterium exchange and rearrangements in the molecular ion of o-(methyl-d₃-thio)benzoic acid lead to fragment ions [M? OD]⁺ as well as [M? OH]⁺ and m/z 106 and 107, just as in the molecular ion of o-methoxybenzoic acid. However, the fragment ion m/z 108 has the composition C₆H₄S rather than C₆H₂D₃CO as it does in the case of o-methoxy-d₃-benzoic acid. By varing the repeller potential at 10 eV (and thus the residence time in the ion source), the corresponding fragments are seen to be formed more slowly from the methylthio acid than from the methoxy acid, which leads to the conclusion that H/D exchange between carboxyl and labelled methylthio is slower than it is between carboxyl and labelled methoxyl.     

Thermodynamic properties of peptide solutions. Part 15. Partial molar isentropic compressibilities of some glycyl dipeptides in aqueous solution at 15 and 35°C

The partial molar isentropic compressibilities at infinite dilution,K _s,2 ^o , have been obtained for eight glycyl dipeptides of sequence gly-X (X is an amino acid) in aqueous solution at the temperatures 15 and 35°C. The results have been combined with those obtained at 25°C, that were reported earlier, to evaluate the temperature dependences ofK _s,2 ^o for the dipeptides in the temperature range 15 to 35°C. TheK _s,2 ^o values for all the dipeptides are negative and increase (become more positive) with an increase in temperature. The slopes of the temperature dependences ofK _s,2 ^o for the dipeptides with typically hydrophobic side-chains are significantly larger than those for dipeptides with hydrophilic side-chains.     

CETYLPYRIDINIUM CHLORIDE + TETRADECYLTRIMETHYLAMMONIUM BROMIDE MIXED MICELLES IN POLYETHYLENE GLYCOL 1000 + WATER MIXTURES*

The conductances of cetylpyridinium chloride (CPyCl) + tetradecyltrimethylammonium bromide (TTAB) mixtures over the entire mole fraction range of CPyCl (x_CPyCl) were measured in aqueous binary mixtures of polyethylene glycol 1000 (PEG 1000) containing 0.5, 1, 2, 5 and 10 wt% of PEG 1000 at 30°C. From the conductivity data, the critical micellar concentration (cmc), degree of counter ion association (χ) and the standard free energy of micelle formation (ΔG^o _M ) of CPyCl and TTAB were computed. The DG^o _M value is further divided into the hydrophobic contribution of free energy of transfer of the surfactant hydrocarbon chain from the medium to the micelle (ΔG^o _HP ), and the energy associated with the surface contributions (ΔG^o _s ) consisting of electrostatic interactions between the head groups and counter ions. Both contributions show a linear dependence on the amount of PEG additive. These results have been explained on the basis of the medium effects of aqueous PEG.

The mixed micelle formation by CPyCl+TTAB show non-ideal behavior which is quite similar in the absence, as well as in the presence, of PEG additive as evaluated by using the regular solution theory. The interaction parameter, b, is always negative and remains almost constant with respect to the amount of PEG additive. This indicates that the mixed micelle formation occurs mainly due to the synergistic interactions between the unlike surfactant monomers only.     

Inverse gas chromatography of lignocellulosic fibers coated with a thermosetting polymer: Use of peak maximum and conder and young methods

The Conder and Young (CY) and the peak maximum (PM) methods were used to estimate the retention time of n-alkane probes on chemithermomechanical pulp (CTMP) wood fibers treated with a low molecular weight grade phenol-formaldehyde resin (PFR). Thermodynamic functions (ΔH_a^o, ΔG_a^o, and ΔS_a^o) and the London dispersive component of the surface energy were derived from these retention times. Treated wood fibers show a high energy surface due to the presence of the thermoset resin on their surface. Values of ΔH_a^o obtained from the CY method were higher than those obtained with the PM method at relatively high temperatures and with relatively low molecular weight alkanes. The results from the two methods were identical at low temperature (293 K) and with the relatively high molecular weight alkane n-undecane.     

Impurity levels and nonlinear optical properties of doped BaTiO3 from extended cluster LDA calculations

The electronic structures of some transition-metal ions doping the ferroelectric oxide BaTiO₃ are calculated through the density functional theory framework (LCAO-LSD ADF method) on extended clusters [XO₆Ba₈Ti₆] embedded in a punctual charge set depicting the crystalline environment. The transition ions X are Feⁿ⁺(n = 2, 3, 4, 5), Ti³⁺, Nb⁴⁺, and Nb⁵⁺. Some related defects like Fe(SINGLE BOND)V_o, where V_o stands for a lacunar oxygen site, are also investigated through a similar process. The positions of impurity levels insides the O_2p(SINGLE BOND)Ti_3d band gap are obtained from eigenvalues and related optical transition or ionization energies are calculated using excited states. This allows us to discuss the photorefractive effect present in such doped materials. The EPR fine-structure parameters a and D are also derived for Fe³⁺ in cubic and tetragonal symmetries from crystal field calculations using parameters drawn from molecular orbital results. © 1997 John Wiley & Sons, Inc.     

Luminescence properties of sol-gel derived silica gels doped and undoped with RE-complexes(RE=Eu,Tb)

The luminescence properties of silica gels and silica gels doped with two rare earth complexes,Eu(TTA)3 and Tb(o-CBA)3 (TTA=thenoyltrifluocetate,o-CBA=o-chlorobenzoic acid) are reported and discussed.Pure silica gels show a blue luminescence,and the maximum excitation and emission wavelengths depend strongly on the solvents used.Both of the studied rare earth complexes exhibit the characteristic emissions of the rare earth ions in silica gels,i.e.,Eu3+5 Do→7 FJ(J=0,1,2,3,4),Tb3+5D4→7FJ(J=3,4,5,6) transitions.Compared with the pure RE-complexes powder,the silica gels doped with RE-complexes show fewer emission lines of the rare earth ions.Furthermore the rare earth ion (Tb3+) presents a longer lifetime (1346μs) in silica gel doped with Tb(o-CBA)3 than in pure Tb(o-CBA)3 powder (744μs).The reasons responsible for these results are discussed in the context.     

Electron impact induced fragmentation of some 7-(o- and p-R-benzylidene)-3-(o- and p-R-phenyl)-3,3a,4,5,6,7-hexahydro-2H-indazoles. I

The mass spectral fragmentation patterns of ten 7-(o- and p-R-benzylidene)-3-(o- and p-R-phenyl)-3,3a,4,5,6,7-hexahydro-2H-indazoles, I, obtained by electron impact have been studied. All the spectra analyzed contain molecular ions and the principal fragmentation routes take place either from the molecular ion, or from (M⁺-1) ion. Likewise, our investigation of the mass spectra of these compounds revealed interesting relationships between the substitution pattern in the framework of I and the fragmenation pathways.     

Thermodynamic properties of peptide solutions: 7. Partial molar isentropic pressure coefficients of some dipeptides in aqueous solution

The partial molar isentropic pressure coefficients at infinite dilution, K _S,2 ^o , have been determined for a number of dipeptides in aqueous solution at 25°C. For a series of dipeptides of sequence gly-X, where X is an amino acid with a neutral side chain, the K _S,2 ^o values are all more negative than that for diglycine. The results are discussed in terms of the hydration of the side chains. There are significant differences in the K _S,2 ^o values for sequence isomeric dipeptides. These differences can be rationalized in terms of the mutual interactions between the side chain and the ionic end groups in the dipeptides. Possible relationships between K _S,2 ^o and V ₂ ^o , the partial molar volume at infinite dilution, were investigated. For the dipeptides of sequence gly-X there is an interesting linear relationship between K _S,2 ^o /V ₂ ^o and V ₂ ^o .     

On the apparent ketonization of the [M?C2H4]+ ion from o-hydroxybutyrophenone

Deuterium labelling and kinetic energy release measurements have shown that the initially enolic [M? C₂H₄]⁺ ions from o-hydroxybutyrophenone have rearranged to o-hydroxyacetophenone ions, if they eliminate a methyl radical.     

Mass spectrometry of cycloheptatriene derivatives. III—skeletal rearrangements in the molecular ion of 7-cyano-7-methylcycloheptatriene and in some of its fragment ions

It is shown by carbon and deuterium labelling experiments that a substantial part of the molecular ions of 7-cyano-7-methylcycloheptatriene has rearranged to a tolylacetonitrile, both in the ion source and in the second field free region. The evidence follows from a comparative study of α-methylbenzylcyanide, o- and p-tolylacetonitriles and their labelled analogues. The decomposing [M — CH₃]⁺ ion from 7-cyano-7-methylcycloheptatriene presumably has a cyanomethylphenyl cation, instead of a cyanotropylium structure.     

Electron impact studies—LXV: Negative-ion mass spectrometry of functional groups 2-aryl-1,3-dithianes

The negative-ion mass spectra of 2-aryl-1,3-dithianes contain pronounced molecular anions together with fragment ions which are produced by both simple and complex cleavage reactions. These spectra contain further examples of specific hydrogen scrambling processes in negative ions. Nitroaryldithianes give intense negative-ion spectra, and that of the o-nitro derivative exhibits an unusual proximity effect. The fragmentation patterns have been examined using both ²H and ¹³C labelling and the metastable defocusing technique.     

Mass Spectral Fragmentation Patterns of 11-(o- and p-R-Anilino)-5H-dibenzo[b,e][1,4]diazepines. IV

The mass spectral fragmentation patterns of eleven 11-(o- and p-R-anilino)-5H-dibenzo[b,e][1,4]diazepines obtained by electron impact have been studied. All the spectra analyzed contain molecular ions, which are base peak for para isomers and the principal fragmentation routes takes place either from the molecular ion, or from (M⁺ - 1) ion. There are, however, some deviations from the general fragmentation pattern in the case of 1,4-dibenzodiazepines with o-amino and p-methoxy substituents caused by direct interaction of these groups with the dibenzodiazepine ring.