Identification of organic hydroperoxides and hydroperoxy acids in secondary organic aerosol formed during the ozonolysis of different monoterpenes and sesquiterpenes by on‐line analysis using atmospheric pressure chemical ionization ion trap mass spectrometry

On‐line ion trap mass spectrometry (ITMS) enables the real‐time characterization of reaction products of secondary organic aerosol (SOA). The analysis was conducted by directly introducing the aerosol particles into the ion source. Positive‐ion chemical ionization at atmospheric pressure (APCI(+)) ITMS was used for the characterization of constituents of biogenic SOA produced in reaction‐chamber experiments. APCI in the positive‐ion mode usually enables the detection of [M+H]⁺ ions of the individual SOA components. In this paper the identification of organic peroxides from biogenic volatile organic compounds (VOCs) by on‐line APCI‐ITMS is presented. Organic peroxides containing a hydroperoxy group, generated by gas‐phase ozonolysis of monoterpenes (α‐pinene and β‐pinene) and sesquiterpenes (α‐cedrene and α‐copaene), could be detected via on‐line APCI(+)‐MS/MS experiments. A characteristic neutral loss of 34 Da (hydrogen peroxide, H₂O₂) in the on‐line MS/MS spectra is a clear indication for the existence of an organic peroxide, containing a hydroperoxy functional group. Copyright © 2009 John Wiley & Sons, Ltd.     

The loss of SO2H from an imido-sulfite under electron impact: Structural elucidation by collision activation of the resulting fragment

Electron impact mass spectrometry of an imido-sulfite 5,6-benzo-2-imino-N-(2,4,6-trichlorophenyl)-1,3-dioxa-2-thiacycloheptane shows an intense fragment ion corresponding to the expulsion of SO₂H from the molecular ion. A mechanism that requires a rearrangement of the molecular ion is proposed. Structural elucidation of the [M? SO₂H]⁺ ion was obtained by recording its metastable ion and collisional activation spectra. Comparison of these spectra with similar spectra recorded from a precursor ion of known structure demonstrated that they were identical. Thus, the results support the proposed structure which derives from the expulsion of SO₂H from the molecular ion of the compound 5,6-benzo-2-imino-N-(2,4,6-trichlorophenyl)-1,3-dioxa-2-thiacycloheptane.     

Electron impact induced cyclization of ortho-substituted diphenylmethanes

Mass spectra of 2-hydroxydiphenylmethane and its derivatives are characterized in the upper mass region by an abundant ion m/z 165. Metastable ion measurements reveal that this ion is formed from the molecular ion of the parent compound by elimination of H₂O and hydrogen. A fluorenyl cation structure is proposed for this ion on the basis of identity of collision induced mass analyzed ion kinetic energy spectra of ion m/z 165 generated from 2-hydroxydiphenylmethane and from fluorene. Four different pathways of formation of a fluorenyl cation are discussed. The contribution of each of these to the genesis of fragment m/z 165 was monitored in a reversed geometry instrument by measuring the first fragmentation in the first field free region and the second fragmentation in the second field free region.     

The fragmentation of ortho-methoxyphenyl-2-propanone oximes and related compounds–further examples of an ortho-effect

An [M ? 31]⁺ ion was a prominent fragment in the mass spectra of three ortho-methoxy-phenyl-2-propanone oximes and is shown to be due to the expulsion of a methoxyl radical from the molecular ion as a result of an ortho-effect. In contrast, an [M ? 31]⁺ ion was absent from the spectra of a structurally related ketone and a hydroxylamine, and was not observed in the spectra of meta- and para-methoxyphenyl-2-propanone oximes.     

13C NMR Spectra of organic peroxides

Conclusions A study has been made of the¹³C NMR spectra of hydroperoxides, peroxides, peroxy esters, and diacyl peroxides.The signal of the carbon atoms of a hydrocarbon radical present in the-position relative to the peroxide group is shifted downfield in comparison with the nonperoxide analog. The replacement of -O- by an -OO-group at a carbonyl carbon produces an upfield shift of the signal from this atom.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 271–275, February, 1982.The authors wish to express their appreciation to P. P. Chernov for recording the spectra, and to I. I. Chervin for participating in discussion of this work.     

The modern mass spectrometer—a complete chemical laboratory

Using nitrobenzene as an example, various ways in which a contemporary mass spectrometer can be utilized to yield a wealth of information about the compound studied are reviewed. Applying a variety of different techniques and procedures, in addition to the conventional low resolution mass spectrum, the following nitrobenzene spectra have been obtained: collision induced dissociation mass spectrum, mass analysed ion kinetic energy spectra, collision induced dissociation mass analysed ion kinetic energy spectra, spectra obtained at constant B/E, spectra obtained at constant B²/E, high voltage scans of metastable ion fragmentation processes, consecutive fragmentations in different field free regions, charge exchange mass spectra, charge stripping mass spectra, doubly charged ion mass spectra, chemical ionization mass spectra, negative ion mass spectra, negative ion mass analysed ion kinetic energy spectra, negative ion mass analysed ion kinetic energy collision induced dissociation spectra, charge inversion spectra, etc. The complementary types of information available from the above studies are discussed to show the unique versatility of mass spectrometry as a technique for the examination of organic compounds.     

The ion kinetic energy and mass spectra of isomeric methyl indoles

The mass spectra of the seven isomeric methylindoles were recorded and the [metastable ion]/[daughter ion] ratios for the reactions m/e 130 → m/e 103 and m/e 103 → m/e 77 have been obtained. The ratios indicate that the decomposing [M — 1] ions (m/e 130) from the 4, 5, 6 and 7 isomers are energetically similar as are the [M — 1] ions from the 2 and 3 isomers. The results observed for the m/e → 103 m/e 77 reaction showed that the decomposing m/e 103 ions from the 2, 3, 4, 5, 6 and 7 isomers all have the same energy distribution. N-Methylindole gave ratios which were similar to the 4 to 7 isomers at 70eV but different at 20 eV. The ion kinetic energy (IKE) spectra of all the isomeric methylindoles were also obtained and the results compared with the data obtained from the [metastable ion]/[daughter ion] approach. The results from the IKE spectra indicated that the energy distributions of the [M — 1] and [(M — 1) — HCN] ions from 1-methylindole and the [(M — 1) — HCN] ions from 2-methylindole could readily be distinguished from other isomers whose [metastable ion]/[daughter ion] ratios were similar. Thus by using both techniques certain ambiguities can be resolved.     

Doubly charged ion mass spectra: VI—Amines

Doubly charged ion mass spectra of 22 amines (2–10 carbon atoms) were determined using an Hitachi RMU-7L double focusing mass spectrometer. Molecular ions were not observed in the spectra of aliphatic amines. The most intense product ion peaks in the spectra of lower molecular weight amines resulted from hydrogen elimination from the molecular ion; however, as amine molecular weight increased the largest peaks resulted from both hydrogen and heavy atom elimination from the molecular ion. Dominant ions in the doubly charged ion spectra of lower molecular weight aliphatic amines were from reactions of [C_nH₃N]²⁺ (n:=2, 3, 4) type ions. The spectra of higher molecular weight aliphatic amines spanned a wide mass range. Appearance energies for some of the more prominent ions were measured in the range from 25 to 49 eV. A geometry optimized quantum mechanical self-consistent field molecular orbital treatment was used to compute the energies and structural parameters of prominent ions in the doubly charged ion mass spectra.     

What is the Structure of b2 Ions Generated from Doubly Protonated Tryptic Peptides?

A recent statistical study (Savitski, M. M.; Falth, M.; Eva Fung, Y. M.; Adams, C. M.; Zubarev, R. A. J. Am. Soc. for Mass Spectrom. doi: 10.1016/j.jasms.2008.08.003) of a large spectral database indicated that the product ion spectra of doubly protonated tryptic peptides fall into two distinct classes. The main factor distinguishing the two classes is the relative abundance of the y _N-2 fragment: for Class I spectra y _N-2 is the most abundant y fragment while for Class II other y ions dominate the corresponding spectra. To explain the dominance of y _N-2 for Class I spectra formation of a nontraditional b ₂ ion with a diketopiperazine (6-membered cyclic peptide) rather than an oxazolone structure was proposed. Here we present evidence from tandem mass spectrometry, hydrogen/deuterium exchange, and density functional calculations that do not support this proposal. Namely, that CID of doubly protonated YIGSR, YGGFLR, and YIYGSFK produce Class I product ion spectra, yet the b ₂ fragment is shown to have the traditional oxazolone structure.     

Mass spectra of sterically crowded trialkylsilyl derivatives of nucleosides

The electron impact mass spectra of tert-butyldimethylsilyl-, cyclo-tetramethylene-tert-butylsilyl and cyclo-tetramethylene-isopropylsilyl- ether derivatives of ribo- and 2′-deoxyribonucleosides are described in detail. The interpretation of fragmentation pathways of full and mixed derivatives was aided by metastable ion decomposition studies, precise mass and deuterium labelling measurements, and spectra of mixed derivatives containing the ‘passive’ (in these spectra) trimethylsilyl group. The sterically crowded silyl groups have a powerful fragmentation directing effect. Elimination of a bulky radical, R˙ (tert-butyl or isopropyl), from the molecular ion produces the siliconium ion [M? R]⁺, which is the precursor for most of the other prominent ions in the spectra. These arise from ‘siliconium ion rearrangements’ resulting from the interaction of the positively charged siliconium ion center with electron dense regions (i.e. oxygens) in the molecule, to form cyclic silyloxonium ions which subsequently decompose. Since the interacting oxygen and silicon must be sterically accessible, the fragment ion types and their abundances are very dependent upon structure. Consequently, [M? R]⁺ ions formed from 2′, 3′ or 5′-O-silyl groups give rise to different sets of daughter ions which, for the most part, are not found, or have very low abundances, in the mass spectra of underivatized or trimethylsilylated nucleosides. Detailed information on sugar and base moieties and isomeric substitution is readily obtained.     

Mass spectra of phenoxyacetyl derivatives

The electron-impact-induced mass spectra of substituted N-phenylphenoxyacetamides are discussed. The structure of the rearrangement ion at m/z 108 is investigated and compared with the molecular ion of anisole by metastable ion and corrected collisionally activated dissociation spectra.     

Ionen-Cyclotron-Resonanz-Messungen von Ion/Molekül-Reaktionen bei Chinonen

At a pressure of 10^?6 Torr the ion cyclotron resonance spectra of p-benzoquinone, methyl-p-benzoquinone, tetramethyl-p-benzoquinone and tetrafluoro-p-benzoquinone are identical to the normal mass spectra. Above 10^?5 Torr the spectra show a variety of signals for product ions. From double resonance measurements it was shown that all the product ions are formed by addition of the molecular ion or of a fragment ion to a neutral quinone molecule. In most cases the addition is accompanied by the elimination of carbon monoxide.     

Stereospecific adduct ion formation in the chemical ionization mass spectra of E- and Z-1,2,3-triaryl-2-propen-1-ones

Stereospecific adduct ion formation has been observed in the chemical ionization mass spectra (positive and negative) of certain E- and Z-1,2,3-triaryl-2-propen-1-ones. The Z isomers are found to give higher relative abundances of adduct ions than the E isomers. This has been interpreted in terms of the differences in the proton affinities of the isomers originating from their different degrees of enone resonance. Halide ion (CI^? and Br^?) attachment spectra of these compounds also show stereochemical differences in the relative abundances of [M]^?˙ and [M+halide]^? ions, though the effect is not as pronounced as in the case of the positive ion spectra.     

Electron impact and chemical ionization mass spectra of bis(methoxycarbonyl) [2.2](2,5)pyridinophanes. Formation of quinolizinium ions under electron impact

For four isomeric bis(methoxycarbonyl)[2.2](2,5)pyridinophanes differing only in the mutual orientation of the two nicotinic ester units, electron impact mass spectra were measured. The fragmentations observed distinguish surprisingly well between the isomers, depending on the transannular substitution pattern. Of special interest is that for one isomer the otherwise unimportant ion at m/z 298 is found as base peak. This ion is formed by expulsion of HCN from the molecular ion, transannular cycloaddition and aromatization to a stable quinolizinium ion. Fragmentation pathways of the isomers are compared, and chemical ionization and negative ion chemical ionization mass spectra are discussed.     

Electron paramagnetic resonance study of nitroxides generated from nitric oxide by reaction with transient radicals

Photochemical or thermal decomposition of azo‐compounds (such as 2,2^′‐azobisisobutyronitrile, 2,2^′‐azobis(2‐methylpropionamidine) dihydrochloride, dialkyl peroxides (such as tert‐butyl peroxide and diacyl peroxides (such as benzoyl peroxide) in anaerobic nitric oxide (NO)‐saturated dimethylsulfoxide (DMSO) or aqueous solutions yielded nitroxides. Well‐characterized electron paramagnetic resonance spectra of nitroxides revealed that NO was favorable for reacting with carbon‐centered and less stereo‐inhibited transient alkyl radicals, giving kinds of nitrosoalkane, typically nitrosomethane, which act sequentially as C‐nitroso compounds to trap transient radicals present in solution, yielding spin‐trapping adducts, i.e. nitroxides. Radicals, including sulfinyl radicals from UV‐irradiated DMSO, were trapped by the in situ formed CH₃NO. O‐centered radicals could not add to the freshly formed C‐nitroso compounds. Possible mechanisms are suggested. Copyright © 2002 John Wiley & Sons, Ltd.     

Mass spectometry of aralkyl compounds with a functional group—VI1: Mass spectra of 1-phenylethyanol-1, 2-phenylethanol-1 and 1-phenylpropanol-2

Mass spectra of 1-phenylethanol-1 and its analogues, specifically deuterated in the aliphatic chain, suggest that the [M? CH₃]⁺ ion is represented partly by an α-hydroxybenzyl fragment. Moreover, the molecular ion loses successively—after scrambling of all hydrogen atoms, except those of CH₃? a hydrogen atom and C₆H₆, generation the CH₃CO⁺ ion. Diffuse peaks, found in the spectra of of 2-phenylethanol-1 and its analogues, specifically deuterated in the aliphatic chain and in the phenyl ring, show that the molecular ion loses C₂H₄O, possibly via a four-center mechanism, after an exchange of aromatic and hydroxylic hydrogens. Mass spectra of 1-phenylpropanol-2 and its analogues, specifically, deuterated in the aliphatic chain, demonstrate that in the molecular ion exclusively the hydroxyl hydrogen atom is transferred to one of the ortho-positions of the phenyl ring via a McLafferty rearrangement, generating the [M ? C₂H₄O]⁺ ion. Furtherore, an eight-membered ring structure is proposed for the [M ? CH₃]⁺ ion to explain the loss of H₂O and C₂H₂O from this ion after an extensive scrambling of hydrogen atoms.     

Analogs of sparteine. IV. Mass spectral features of a series of N,N′-disubstituted bispidines

The mass spectra of a series of N, N′-disubstituted bispidinc derivatives have been investigated, and salient features analogous to those seen in the spectra of related azabieyelie compounds observed. The most important feature observed in the spectra is the common base peak (m/e 58), which results from the generation of N, N-dimethylformimmonium ion 24. The pathway by which this ion originates is discussed.     

Determination of ion structures in structurally related compounds using precursor ion fingerprinting

Structurally-related alkaloids were analyzed by electrospray ionization/multiple stage mass spectrometry (ESI/MS ⁿ ) at varying collision energies to demonstrate a conceptual algorithm, precursor ion fingerprinting (PIF). PIF is a new approach for interpreting and library-searching ESI mass spectra predicated on the precursor ions of structurally-related compounds and their matching product ion spectra. Multiple-stage mass spectra were compiled and constructed into “spectral trees” that illustrated the compounds’ product ion spectra in their respective mass spectral stages. The precursor ions of these alkaloids were characterized and their spectral trees incorporated into an MS ⁿ library. These data will be used to construct a universal, searchable, and transferable library of MS ⁿ spectra. In addition, PIF will generate a proposed structural arrangement utilizing previously characterized ion structures, which will assist in the identification of unknown compounds.     

Ortho effects in organic molecules on electron impact: 18—Novel hydrogen transfer from the methoxy group to acetylenic carbon in 2-methoxyphenylacetylene and 2-methoxydiphenylacetylenes

The transfer of a hydrogen from the ortho methoxy group to the acetylenic carbon in 2-methoxyphenylacetylene under electron impact conditions affords the rearranged molecular ion corresponding to 2H-1-benzopyran. Similar processes leading to cyclic products are also noticed in 2-methoxydiphenylacetylenes. The ion structures and the mechanism of fragmentations are established through high-resolution data, collision-induced decomposition, mass-analysed ion kinetic energy spectra, B/E linked scan spectra, D-labelling and chemical substitution.     

Mass spectrometry of trialkylsilyl and acyl derivatives of 2′-deoxynucleosides

The electron impact mass spectra of monosilyl and mixed acyl-silyl derivatives of 2′-deoxynucleosides are described in detail. (Silyl = tert-butyldimethylsilyl, cyclo-tetramethylene-isopropylsilyl, or cyclo-tetramethylene-tert-butylsilyl; acyl = acetyl or trifluoroacetyl.) The interpretation of the fragmentation pathways was aided by metastable ion decomposition studies, precise mass and deuterium labelling measurements. Mass spectrally, the acyl substituents are mostly ‘passive’ and have (with possibly one exception) little fragmentation directing capability. In contrast, the silyl groups have powerful fragmentation directing properties. Elimination of the bulky alkyl radical R^˙ (tert-butyl or isopropyl) from the molecular ion produces the siliconium ion, [M–R]⁺, which is the precursor for most of the other prominent ions in the spectra. These arise from ‘siliconium ion rearrangements’ resulting from the interaction of the positively charged siliconium ion centre with the electron dense regions (i.e. oxygens) in the molecule, to form cyclic silyloxonium ions which subsequently decompose. Since the interacting oxygen and silicon must be sterically accessible, the fragment ion types and their abundances are very dependent upon structure. Consequently, [M–R]⁺ ions formed from 3′- or 5′-O-silyl groups give rise to different sets of daughter ions which, for the most part, are not found, or have very low abundances, in the mass spectra of underivatized or trimethylsilylated nucleosides. Detailed information on sugar and base moieties and isomeric substitution is readily obtained.