Unimolecular metastable decompositions of gem-dimethoxyalkanes (RR'C(OCH(3))(2)) upon electron impact. I. Dimethoxymethane and 1, 1-dimethoxyethane

The unimolecular metastable decompositions of dimethoxymethane (CH(2)(OCH(3))(2), 1) and 1,1-dimethoxyethane (CH(3)CH(OCH(3))(2), 2) upon electron impact have been investigated by means of mass-analyzed ion kinetic energy (MIKE) spectrometry, collision-induced dissociation (CID) spectrometry and D-labeling techniques. Both molecular ions are formed at extremely low abundance. Sequential transfers of a methyl group and a hydrogen atom to an ether oxygen are observed during the decomposition of [M - H](+) ions from 1 and 2. The [M - H](+) ion from 2 also decomposes into the m/z 43 ion by the loss of dimethyl ether. Almost complete hydrogen exchange is observed prior to the loss of CH(4) from the m/z 45 ion ([M - OCH(3)](+)) of 1. The m/z 59 ions ([M - OCH(3)](+)) of 2 decompose competitively into the m/z 31 and 29 ions by the losses of C(2)H(4) and CH(2)O, respectively. The former loss occurs via two different fragmentation pathways. The relative abundances of the ions in the MIKE spectra increase with decreases in the total heat of formation (Sigma DeltaH(f)) of the ion plus the neutral fragment. Copyright 2000 John Wiley & Sons, Ltd.     

Metastable ion study of organosilicon compounds. Part XIII: dimethoxydimethylsilane, (CH(3))(2)Si(OCH(3))(2), and dimethoxymethylsilane, CH(3)SiH(OCH(3))(2)

Unimolecular metastable fragmentations of dimethoxydimethylsilane, (CH(3))(2)Si(OCH(3))(2) (MW 120, 1), and dimethoxymethylsilane, CH(3)SiH(OCH(3))(2) (MW 106, 2), upon electron impact ionization have been studied by means of mass-analyzed ion kinetic energy (MIKE) spectrometry and the D-labeling technique in conjunction with thermochemistry. The results have been compared with those of the corresponding carbon analogues, 2,2-dimethoxypropane, (CH(3))(2)C(OCH(3))(2) (MW 104, 3) and 1,1-dimethoxyethane, CH(3)CH(OCH(3))(2) (MW 90, 4). In analogy with the cases of 3 and 4, both molecular ions from 1 and 2 are formed at very low abundance at 70 eV, and begin to decompose by the expulsion of the substituents (H, CH(3) or OCH(3)) on the central silicon atom. These decompositions are followed by the loss of a formaldehyde molecule (CH(2)O), as commonly observed in the mass spectra of methoxysilanes. Further, an ethylene (C(2)H(4)) or a dimethyl ether (CH(3)OCH(3)) molecule loss is observed in the fragmentation of some intermediate ions generated from 1(+)* and 2(+)*, but the mechanisms are different than those in the cases of 3 and 4. Some of these fragmentations are also different than those reported previously. The relative abundance of the ions in many MIKE spectra is explained by the extension of the Stevenson-Audier rule. The reaction, which is in contrast to the rule, however, is rationalized by the energy of the transition state for the reaction, estimated by semi-empirical molecular orbital calculation. The peak at m/z 59 from 2(+)* consists only of CH(3)OSi(+) ion, whereas the peak from 1(+)* consists of two different ions, CH(3)OSi(+) and (CH(3))(2)Si(+)H. The ions CH(3)OSi(+) from 1(+)* and 2(+)* are generated by at least two and three separate routes respectively.     

Metastable ion study of organosilicon compounds. Part XIV-trimethylsilylacetic acid, (CH(3))(3)SiCH(2)COOH, and its methyl ester, (CH(3))(3)SiCH(2)COOCH(3)

The unimolecular metastable decompositions of trimethylsilylacetic acid, (CH(3))(3)SiCH(2)COOH (1), and its methyl ester, (CH(3))(3)SiCH(2)COOCH(3) (2), were investigated by mass-analyzed ion kinetic energy (MIKE) spectrometry in conjunction with thermochemical data. The abundance of the molecular ions of both compounds, generated by electron ionization, is extremely low. However, the abundance of the ions generated by the loss of (.)CH(3) and observed at m/z 117 and 131 is moderate. These fragment ions further decompose to form the most abundant m/z 75 and 89 ions, respectively, by the loss of CH(2)CO through a (CH(3))(2)Si group migration. The loss of CH(2)CO is also observed to occur from 2(+.) and its fragment ion at m/z 115 generated by the loss of (.)OCH(3). The former reaction is proposed to occur via an ion-radical complex.     

Synthesis, structure, electrochemistry, and spectroelectrochemistry of hypervalent phosphorus(V) octaethylporphyrins and theoretical analysis of the nature of the PO bond in P(OEP)(CH(2)CH(3))(O)

A variety of phosphorus(V) octaethylporphyrin derivatives of the type [P(OEP)(X)(Y)](+)Z(-) (OEP: octaethylporphyrin) (X = CH(3), CH(2)CH(3), C(6)H(5), F; Y = CH(3), CH(2)CH(3), OH, OCH(3), OCH(2)CH(3), On-Pr, Oi-Pr, Osec-Bu, NHBu, NEt(2), Cl, F, O(-); Z = ClO(4), PF(6)) were prepared. X-ray crystallographic analysis of eleven compounds reveals that the degree of ruffling of the porphyrin core becomes greater and the average P-N bond distance becomes shorter as the axial ligands become more electronegative. Therefore, the electronic effect of the axial substituents plays a major role in determining the degree of ruffling although the steric effect of the substituents plays some role. A comparison of the (1)H NMR chemical shifts for the series of [P(OEP)(CH(2)CH(3))(Y)](+)Z(-) complexes with those of the corresponding arsenic porphyrins, which possess a planar core, indicates a much smaller ring current effect of the porphyrin core in the severely ruffled phosphorus porphyrins. The electrochemistry, spectroelectrochemistry and ESR spectroscopy of the singly reduced compounds are also discussed. The OH protons of [P(OEP)(X)(OH)](+) are acidic enough to generate P(OEP)(X)(O) by treatment with aq dilute NaOH. X-ray analysis of P(OEP)(CH(2)CH(3))(O) reveals that the PO bond length is very short (1.475(7) A) and is comparable to that in triphenylphosphine oxide (1.483 A). The features of the quite unique hexacoordinate hypervalent compounds are investigated by density functional calculation of a model (Por)P(CH(2)CH(3))(O) and (Por)P(F)(O) (Por: unsubstituted porphyrin).     

Preparation and Crystal Structure of Hetero-metal Clusters [h5-C5H4C(O)CH2CH2C(O)OCH3]FeCoM(m3-S)(CO)8 (M = Mo or W)

The hetero-metal clusters [h5-C5H4C(O)CH2CH2C(O)OCH3]FeCoM(m3-S)(CO)8 (M = Mo 1, M = W 2) were prepared by thermal reactions of FeCo2(CO)9(m3-S) with metal exchange reagent [h5-C5H4C(O)CH2CH2C(O)OCH3]M(CO)3Na (M = Mo or W) in THF. Cluster 1 reacted with 2,4-dinitrophenylhydrazine at room temperature to yield the cluster hydrazone derivative (m3-S)CoFeMo(CO)8[h5-C5H4C(NR)Me] [R = NHC6H3-2,4-(NO2)2] 3. All the compounds were characterized by elemental analyses, IR and NMR spectra. Cluster 1 was determined by single crystal X-ray diffraction. Crystal data: C18H11O11SCoFeMo, Mr = 646.05, triclinic, space group P_1, a = 8.148(2), b = 10.685(3), c = 13.410(4) ?, a = 100.077(5), b = 102.452(5), g = 91.108(6)°, V = 1120.4(5) ?3, Z = 2, Dc = 1.915 g/cm3, F(000) = 636, m = 2.071 mm-1, the final R = 0.0378 and wR = 0.0968 for 5074 observations with (I > 2s(I)).     

Dimethyl ether chemical ionization of arylalkylamines

The gas-phase reactions of dimethyl ether (DME) ions with a number of biologically active arylalkylamines of the general formula R(1)R(2)C(6)H(3)CHR(3)(CH(2))(n)NR(4)R(5), where R(1) = H or OH, R(2) = H, F, NO(2), OH or OCH(3), R(3) = H or OH, R(4) and R(5) = H or CH(3), have been studied by means of chemical ionization mass spectrometry. Under the experimental conditions used, the most abundant DME ion is the methoxymethyl cation (CH(3)OCH(2)(+), m/z 45). The unimolecular metastable decompositions of the [M + 45](+), [M + 13](+) and [M + 15](+) adducts formed have been interpreted in terms of the initial site of reaction with the amines and the presence of different functional groups in the molecule. This has permitted establishment of general fragmentation patterns for the adducts, and their correlation with structural features of the molecules. The main site of reaction of the ion CH(3)OCH(2)(+) with the amines seems to be the amino group, particularly if the amine is primary, although a competition with attack on the aromatic ring and especially on the benzylic hydroxy group is observed. In a few cases the reaction mechanisms have been elucidated through the use of deuterated amines obtained by H/D exchange with D(2)O.     

Kinetic energy release of protonated methanol clusters using the low-temperature fast-atom bombardment: experiment and theory combined

Low-temperature fast-atom bombardment was found to be an excellent method for generating large protonated methanol clusters, (CH(3)OH)(n)H(+) (n = 2 to 15). Metastable dissociations of these clusters, involving elimination of one methanol molecule, were studied using mass-analyzed ion kinetic energy spectra (MIKES). From metastable peak profiles kinetic energy release (KER) distributions were obtained, even for clusters as large as (CH(3)OH)(15)H(+). The results were analyzed by a simple thermal model, by the finite heat bath theory (FHBT) and by the RRKM-based MassKinetics algorithm. The KER distribution was shown to correspond to a three-dimensional translational energy distribution, implying statistical energy partitioning in the transition state. The mean KER values and transition state temperatures were found to increase with cluster size, reaching 25 meV and approximately 210 K for large clusters (n = 10).     

Ion-molecule reactions of dimethyl ether cations with polycyclic aromatic hydrocarbons in a quadrupole ion trap mass spectrometer

The reaction chemistry between dimethyl ether (DME) cations and polycyclic aromatic hydrocarbons (PAHs) was elucidated by isolating three different types of DME ions using a quadrupole ion trap and reacting them individually with neutral PAH molecules eluting from a gas chromatographic column. The results obtained show that the CH(2)OCH(3)(+) ion (m/z 45) reacts via adduct formation followed by elimination of CH(3)OH, the (CH(3))(2)OH(+) (m/z 47) ion serves as proton donor and the (CH(3))(3)O(+) ion (m/z 61) does not yield any reaction products. Copyright 1999 John Wiley & Sons, Ltd.     

Fragmentation reactions of protonated peptides containing glutamine or glutamic acid

A variety of protonated dipeptides and tripeptides containing glutamic acid or glutamine were prepared by electrospray ionization or by fast atom bombardment ionization and their fragmentation pathways elucidated using metastable ion studies, energy-resolved mass spectrometry and triple-stage mass spectrometry (MS(3)) experiments. Additional mechanistic information was obtained by exchanging the labile hydrogens for deuterium. Protonated H-Gln-Gly-OH fragments by loss of NH(3) and loss of H(2)O in metastable ion fragmentation; under collision-induced dissociation (CID) conditions loss of H-Gly-OH + CO from the [MH - NH(3)](+) ion forms the base peak C(4)H(6)NO(+) (m/z 84). Protonated dipeptides with an alpha-linkage, H-Glu-Xxx-OH, are characterized by elimination of H(2)O and by elimination of H-Xxx-OH plus CO to form the glutamic acid immonium ion of m/z 102. By contrast, protonated dipeptides with a gamma-linkage, H-Glu(Xxx-OH)-OH, do not show elimination of H(2)O or formation of m/z 102 but rather show elimination of NH(3), particularly in metastable ion fragmentation, and elimination of H-Xxx-OH to form m/z 130. Both the alpha- and gamma-dipeptides show formation of [H-Xxx-OH]H(+), with this reaction channel increasing in importance as the proton affinity (PA) of H-Xxx-OH increases. The characteristic loss of H(2)O and formation of m/z 102 are observed for the protonated alpha-tripeptide H-Glu-Gly-Phe-OH whereas the protonated gamma-tripeptide H-Glu(Gly-Gly-OH)-OH shows loss of NH(3) and formation of m/z 130 as observed for dipeptides with the gamma-linkage. Both tripeptides show abundant formation of the y(2)' ion under CID conditions, presumably because a stable anhydride neutral structure can be formed. Under metastable ion conditions protonated dipeptides of structure H-Xxx-Glu-OH show abundant elimination of H(2)O whereas those of structure H-Xxx-Gln-OH show abundant elimination of NH(3). The importance of these reaction channels is much reduced under CID conditions, the major fragmentation mode being cleavage of the amide bond to form either the a(1) ion or the y(1)' ion. Particularly when Xxx = Gly, under CID conditions the initial loss of NH(3) from the glutamine containing dipeptide is followed by elimination of a second NH(3) while the initial loss of H(2)O from the glutamic acid dipeptide is followed by elimination of NH(3). Isotopic labelling shows that predominantly labile hydrogens are lost in both steps. Although both [H-Gly-Glu-Gly-OH]H(+) and [H-Gly-Gln-Gly-OH]H(+) fragment mainly to form b(2) and a(2) ions, the latter also shows elimination of NH(3) plus a glycine residue and formation of protonated glycinamide. Isotopic labelling shows extensive mixing of labile and carbon-bonded hydrogens in the formation of protonated glycinamide.     

Complexes formed in solution between vanadium(IV)/(V) and the cyclic dihydroxamic acid putrebactin or linear suberodihydroxamic acid

An aerobic solution prepared from V(IV) and the cyclic dihydroxamic acid putrebactin (pbH(2)) in 1:1 H(2)O/CH(3)OH at pH = 2 turned from blue to orange and gave a signal in the positive ion electrospray ionization mass spectrometry (ESI-MS) at m/z(obs) 437.0 attributed to the monooxoV(V) species [V(V)O(pb)](+) ([C(16)H(26)N(4)O(7)V](+), m/z(calc) 437.3). A solution prepared as above gave a signal in the (51)V NMR spectrum at δ(V )= -443.3 ppm (VOCl(3), δ(V) = 0 ppm) and was electron paramagnetic resonance silent, consistent with the presence of [V(V)O(pb)](+). The formation of [V(V)O(pb)](+) was invariant of [V(IV)]:[pbH(2)] and of pH values over pH = 2-7. In contrast, an aerobic solution prepared from V(IV) and the linear dihydroxamic acid suberodihydroxamic acid (sbhaH(4)) in 1:1 H(2)O/CH(3)OH at pH values of 2, 5, or 7 gave multiple signals in the positive and negative ion ESI-MS, which were assigned to monomeric or dimeric V(V)- or V(IV)-sbhaH(4) complexes or mixed-valence V(V)/(IV)-sbhaH(4) complexes. The complexity of the V-sbhaH(4) system has been attributed to dimerization (2[V(V)O(sbhaH(2))](+) ? [(V(V)O)(2)(sbhaH(2))(2)](2+)), deprotonation ([V(V)O(sbhaH(2))](+) - H(+) ? [V(V)O(sbhaH)](0)), and oxidation ([V(IV)O(sbhaH(2))](0) -e(-) ? [V(V)O(sbhaH(2))](+)) phenomena and could be described as the sum of two pH-dependent vectors, the first comprising the deprotonation of hydroxamate (low pH) to hydroximate (high pH) and the second comprising the oxidation of V(IV) (low pH) to V(V) (high pH). Macrocyclic pbH(2) was preorganized to form [V(V)O(pb)](+), which would provide an entropy-based increase in its thermodynamic stability compared to V(V)-sbhaH(4) complexes. The half-wave potentials from solutions of [V(IV)]:[pbH(2)] (1:1) or [V(IV)]:[sbhaH(4)] (1:2) at pH = 2 were E(1/2) -335 or -352 mV, respectively, which differed from the expected trend (E(1/2) [VO(pb)](+/0) < V(V/IV)-sbhaH(4)). The complex solution speciation of the V(V)/(IV)-sbhaH(4) system prevented the determination of half-wave potentials for single species. The characterization of [V(V)O(pb)](+) expands the small family of documented V-siderophore complexes relevant to understanding V transport and assimilation in the biosphere.     

Ionization and dissociation of CH3I in intense laser field

The ionization-dissociation of methyl iodide in intense laser field has been studied using a reflection time-of-flight mass spectrometry (RTOF-MS), at a laser intensity of < or =6.6x10(14) W/cm(2), lambda=798 nm, and a pulse width of 180 fs. With the high resolution of RTOF-MS, the fragment ions with the same M/z but from different dissociation channels are resolved in the mass spectra, and the kinetic energy releases (KERs) of the fragment ions such as I(q+) (q=1-6), CH(m) (+) (m=0-3), C(2+), and C(3+) are measured. It is found that the KERs of the fragment ions are independent of the laser intensity. The fragments CH(3) (+) and I(+) with very low KERs (<1 eV for CH(3) (+) and <0.07 eV for I(+)) are assigned to be produced by the multiphoton dissociation of CH(3)I(+). For the fragments CH(3) (+) and I(+) from CH(3)I(2+), they are produced by the Coulomb explosion of CH(3)I(2+) with the interaction from the covalent force of the remaining valence electrons. The split of the KER of the fragments produced from CH(3)I(2+) dissociation is observed experimentally and explained with the energy split of I(+)((3)P(2)) and I(+)((3)P(0,1)). The dissociation CH(3)I(3+)-->CH(3) (+)+I(2+) is caused by Coulomb explosion. The valid charge distance R(c) between I(2+) and CH(3) (+), at which enhanced ionization of methyl iodide occurs, is obtained to be 3.7 A by the measurements of the KERs of the fragments CH(3) (+) and I(2+). For the CH(3)I(n+) (n> or =3), the KERs of the fragment ions CH(3) (p+) and I(q+) are attributed to the Coulomb repulsion between CH(3) (p+) and I(q+) from R(c) approximately 3.7 A. The dissociation of the fragment CH(3) (+) is also discussed. By the enhanced ionization mechanism and using the measured KER of I(q+), all the possible Coulomb explosion channels are identified. By comparing the abundance of fragment ions in mass spectrum, it is found that the asymmetric dissociation channels with more charges on iodine, q>p, are the dominant channels.     

Water-assisted interconversions and dissociations of the acetaldehyde ion and its isomers. An experimental and theoretical study

The gas-phase reactions of the ion [CH(3)CHO/H(2)O](+*) have been investigated by mass spectrometry. The metastable ion (MI) mass spectrum reveals that this ion-molecule complex decomposes spontaneously by the losses of H(2)O, CO, and (*)CH(3). 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 (*)CH(3). The CO loss produces the [(*)CH(3)...H(3)O(+)] ion and involves a "backside displacement" mechanism. The products corresponding to (*)CH(3) loss have been assigned by theory to be [OC...H(3)O(+)] and [CO...H(3)O(+)], and their 298 K enthalpy values, calculated at the G3 level of theory, are Delta(f)H[OC...H(3)O(+)] = 420 kJ/mol and Delta(f)H[CO...H(3)O(+)] = 448 kJ/mol. The PES describing the interconversions among water-solvated CH(3)CHO(+*), CH(3)COH(+*), and CH(2)CHOH(+*) have been shown to involve proton-transport catalysis (PTC), catalyzed 1,2 H-transfer, and an uncatalyzed H-atom transfer mechanism, respectively.     

Electronic structure and normal vibrations of CH3(OCH2CH2)nOCH3-M+-CF3SO3- (n = 2-4, M = Li, Na, and K)

Electronic structure and the vibrational frequencies of CH(3)(OCH(2)CH(2))(n)OCH(3)-M(+)-CF(3)SO(3)(-) (n = 2-4, M = Li, Na, and K) complexes have been derived from ab initio Hartree-Fock calculations. The metal ion shows varying coordination from 5 to 7 in these complexes. In tetraglyme-lithium triflate, Li(+) binds to one of the oxygens of CF(3)SO(3)(-) (triflate or Tf(-)) unlike for potassium or sodium ions, which possess bidentate coordination. Structures of glyme-MTf complexes thus derived agree well with those determined from X-ray diffraction experiments. The metal ion binds more strongly to ether oxygens of tetraglyme than its di- or triglyme analogues and engenders contraction of SO (for oxygens binding to metal ion) bonds with consequent frequency upshift for the corresponding vibration in the complex relative to those in the free MTf ion pairs. Complexation of the diglyme with LiTf engenders the largest downshift (91 cm(-1)) for the SO(2) stretching vibration of the free anion, which suggests stronger binding of lithium to the diglyme than the tri- (79 cm(-1)) or tetraglyme (70 cm(-1)). A frequency shift in the opposite direction for the SO (where oxygens do not coordinate to the metal) and CF(3) stretchings, which stems from the ion-polymer and anion-ion interactions, has been noticed. These frequency shifts have been analyzed using natural bond orbital analysis and difference electron density maps coupled with molecular electron density topography.     

Gas-phase reactivity of the O=P(OCH3)2+ phosphonium ion with aliphatic esters in a quadrupole ion trap. Spontaneous elimination of ketenes

Ion-molecule reactions between the O=P(OCH(3))(2) (+) phosphonium ions and five aliphatic esters (methyl acetate, methyl propionate, methyl 2-methylpropionate, methyl butyrate and ethyl acetate) were performed in a quadrupole ion trap mass spectrometer. The O=P(OCH(3))(2) (+) phosphonium ions, formed by electron ionization from neutral trimethyl phosphite, were found to react with aliphatic esters to give an adduct ion [RR'CHCOOR", O=P(OCH(3))(2)](+), which loses spontaneously a molecule of ketene CH(2)=CO or substituted ketenes RR'C=CO. Isotope-labeled methyl acetate was used to elucidate fragmentation mechanisms. The potential energy surface obtained from B3LYP/6-31G(d,p) calculations for the reaction between O=P(OCH(3))(2) (+) and methyl acetate is described.     

Analysis of triacetone triperoxide (TATP) and TATP synthetic intermediates by electrospray ionization mass spectrometry

The explosive triacetone triperoxide (TATP) has been analyzed by electrospray ionization mass spectrometry (ESI-MS) on a linear quadrupole instrument, giving a 62.5 ng limit of detection in full scan positive ion mode. In the ESI interface with no applied fragmentor voltage the m/z 245 [TATP + Na](+) ion was observed along with m/z 215 [TATP + Na - C(2)H(6)](+) and 81 [(CH(3))(2)CO + Na](+). When TATP was ionized by ESI with an applied fragmentor voltage of 75 V, ions at m/z 141 [C(4)H(6)O(4) + Na](+) and 172 [C(5)H(9)O(5) + Na](+) were also observed. When the precipitates formed in the synthesis of TATP were analyzed before the reaction was complete, a new series of ions was observed in which the ions were separated by 74 m/z units, with ions occurring at m/z 205, 279, 353, 427, 501, 575, 649 and 723. The series of evenly spaced ions is accounted for as oligomeric acetone carbonyl oxides terminated as hydroperoxides, [HOOC(CH(3))(2){OOC(CH(3))(2)}(n)OOH + Na](+) (n = 1, 2 ... 8). The ESI-MS spectra for this homologous series of oligoperoxides have previously been observed from the ozonolysis of tetramethylethylene at low temperatures. Precipitates from the incomplete reaction mixture, under an applied fragmentor voltage of 100 V in ESI, produced an additional ion observed at m/z 99 [C(2)H(4)O(3) + Na](+), and a set of ions separated by 74 m/z units occurring at m/z 173, 247, 321, 395, 469 and 543, proposed to correspond to [CH(3)CO{OOC(CH(3))(2)}(n)OOH + Na](+) (n = 1,2 ... 5). Support for the assigned structures was obtained through the analysis of both protiated and perdeuterated TATP samples.     

Atmospheric chemistry of a model biodiesel fuel, CH3C(O)O(CH2)2OC(O)CH3: kinetics, mechanisms, and products of Cl atom and OH radical initiated oxidation in the presence and absence of NOx

Relative rate techniques were used to study the kinetics of the reactions of Cl atoms and OH radicals with ethylene glycol diacetate, CH3C(O)O(CH2)2OC(O)CH3, in 700 Torr of N2/O2 diluent at 296 K. The rate constants measured were k(Cl + CH3C(O)O(CH2)2OC(O)CH3) = (5.7 +/- 1.1) x 10(-12) and k(OH + CH3C(O)O(CH2)2OC(O)CH3) = (2.36 +/- 0.34) x 10(-12) cm3 molecule-1 s-1. Product studies of the Cl atom initiated oxidation of ethylene glycol diacetate in the absence of NO in 700 Torr of O2/N2 diluent at 296 K show the primary products to be CH3C(O)OC(O)CH2OC(O)CH3, CH3C(O)OC(O)H, and CH3C(O)OH. Product studies of the Cl atom initiated oxidation of ethylene glycol diacetate in the presence of NO in 700 Torr of O2/N2 diluent at 296 K show the primary products to be CH3C(O)OC(O)H and CH3C(O)OH. The CH3C(O)OCH2O* radical is formed during the Cl atom initiated oxidation of ethylene glycol diacetate, and two loss mechanisms were identified: reaction with O2 to give CH3C(O)OC(O)H and alpha-ester rearrangement to give CH3C(O)OH and HC(O) radicals. The reaction of CH3C(O)OCH2O2* with NO gives chemically activated CH3C(O)OCH2O* radicals which are more likely to undergo decomposition via the alpha-ester rearrangement than CH3C(O)OCH2O* radicals produced in the peroxy radical self-reaction.     

Dehydration reaction of hydroxyl substituted alkenes and alkynes on the Ru(2)S(2) complex

A variety of inter- and intramolecular dehydration was found in the reactions of [[Ru(P(OCH(3))(3))(2)(CH(3)CN)(3)](2)(mu-S(2))](CF(3)SO(3))(4) (1) with hydroxyl substituted alkenes and alkynes. Treatment of 1 with allyl alcohol gave a C(3)S(2) five-membered ring complex, [[Ru(P(OCH(3))(3))(2)(CH(3)CN)(3)](2)[mu-SCH(2)CH(2)CH(OCH(2)CH=CH(2))S]](CF(3)SO(3))(4) (2), via C-S bond formation after C-H bond activation and intermolecular dehydration. On the other hand, intramolecular dehydration was observed in the reaction of 1 with 3-buten-1-ol giving a C(4)S(2) six-membered ring complex, [[Ru(P(OCH(3))(3))(2)(CH(3)CN)(3)](2) [mu-SCH(2)CH=CHCH(2)S]](CF(3)SO(3))(4) (3). Complex 1 reacts with 2-propyn-1-ol or 2-butyn-1-ol to give homocoupling products, [[Ru(P(OCH(3))(3))(2)(CH(3)CN)(3)](2)[mu-SCR=CHCH(OCH(2)C triple bond CR)S]](CF(3)SO(3))(4) (4: R = H, 5: R = CH(3)), via intermolecular dehydration. In the reaction with 2-propyn-1-ol, the intermediate complex having a hydroxyl group, [[Ru(P(OCH(3))(3))(2)(CH(3)CN)(3)](2)[mu-SCH=CHCH(OH)S]](CF(3)SO(3))(4) (6), was isolated, which further reacted with 2-propyn-1-ol and 2-butyn-1-ol to give 4 and a cross-coupling product, [[Ru(P(OCH(3))(3))(2)(CH(3)CN)(3)](2)[mu-SCH=CHCH(OCH(2)C triple bond CCH(3))S]](CF(3)SO(3))(4) (7), respectively. The reaction of 1 with diols, (HO)CHRC triple bond CCHR(OH), gave furyl complexes, [[Ru(P(OCH(3))(3))(2)(CH(3)CN)(3)](2)[mu-SSC=CROCR=CH]](CF(3)SO(3))(3) (8: R = H, 9: R = CH(3)) via intramolecular elimination of a H(2)O molecule and a H(+). Even though (HO)(H(3)C)(2)CC triple bond CC(CH(3))(2)(OH) does not have any propargylic C-H bond, it also reacts with 1 to give [[Ru(P(OCH(3))(3))(2)(CH(3)CN)(3)](2)[mu-SCH(2)C(=CH(2))C(=C=C(CH(3))(2))]S](CF(3)SO(3))(4) (10). In addition, the reaction of 1 with (CH(3)O)(H(3)C)(2)CC triple bond CC(CH(3))(2)(OCH(3)) gives [[Ru(P(OCH(3))(3))(2)(CH(3)CN)(2)][mu-S=C(C(CH(3))(2)OCH(3))C=CC(CH(3))CH(2)S][Ru(P(OCH(3))(3))(2)(CH(3)CN)(3)]](CF(3)SO(3))(4) (11), in which one molecule of CH(3)OH is eliminated, and the S-S bond is cleaved.     

Atmospheric chemistry of C2F5CH2OCH3 (HFE-365mcf)

FTIR smog chamber techniques were used to measure k(Cl + C(2)F(5)CH(2)OCH(3)) = (2.52 ± 0.37) × 10(-11) and k(OH + C(2)F(5)CH(2)OCH(3)) = (5.78 ± 1.02) × 10(-13) cm(3) molecule(-1) s(-1) in 700 Torr of air diluent at 296 ± 1 K. The atmospheric lifetime of C(2)F(5)CH(2)OCH(3) is estimated to be 20 days. Reaction of chlorine atoms with C(2)F(5)CH(2)OCH(3) proceeds 18 ± 2% at the -CH(2)- group and 82 ± 2% at the -CH(3) group. Reaction of OH radicals with C(2)F(5)CH(2)OCH(3) proceeds 44 ± 5% at the -CH(2)- group and 56 ± 5% at the -CH(3) group. The atmospheric fate of C(2)F(5)CH(2)OCH(2)O radicals is reaction with O(2) to give C(2)F(5)CH(2)OCHO. The atmospheric fate of C(2)F(5)CH(O)OCH(3) radicals is C-C bond-cleavage to give C(2)F(5) radicals and CH(3)OCHO (methyl formate). The infrared spectrum was recorded and used to estimate a global warming potential of 6 (100 year time horizon) for C(2)F(5)CH(2)OCH(3).     

Unusual atmospheric pressure chemical ionization conditions for detection of organic peroxides

Organic peroxides such as the cumene hydroperoxide I (M(r) = 152 u), the di-tert-butyl peroxide II (M(r) = 146 u) and the tert-butyl peroxybenzoate III (M(r) = 194 u) were analyzed by atmospheric pressure chemical ionization mass spectrometry using a water-methanol mixture as solvent with a low flow-rate of mobile phase and unusual conditions of the source temperature (< or =50 degrees C) and probe temperature (70-200 degrees C). The mass spectra of these compounds show the formation of (i) an [M + H](+) ion (m/z 153) for the hydroperoxide I, (ii) a stable adduct [M + CH(3)OH(2)](+) ion (m/z 179) for the dialkyl peroxide II and (iii) several protonated adduct species such as protonated molecules (m/z 195) and different protonated adduct ions (m/z 227, 389 and 421) for the peroxyester III. Tandem mass spectrometric experiments, exact mass measurements and theoretical calculations were performed for characterize these gas-phase ionic species. Using the double-well energy potential model illustrating a gas-phase bimolecular reaction, three important factors are taken into account to propose a qualitative interpretation of peroxide behavior toward the CH(3)OH(2) (+), i.e. thermochemical parameters (DeltaHdegrees(reaction)) and two kinetic factors such as the capture constant of the initial stable ion-dipole and the magnitude of the rate constant of proton transfer reaction into the loose proton bond cluster.     

Electrospray ionization ion-trap time-of-flight tandem mass spectrometry of two furofurans: sesamin and gmelinol

High-resolution electrospray ionization multistage tandem mass spectrometry (MS(1-7)) in positive ion mode was used to determine the accurate masses and the fragmentation pathways of two furofurans, sesamin and gmelinol. The protonated molecules [M+H]+ were absent in the conventional mass spectra of both compounds, but two characteristic ions, [M+H-H(2)O]+ and [M+H-H(2)]+, were always observed. Successive losses of CH(2)O and CO are the common characteristic fragmentations. Based on the exact masses acquired from 21 different tandem mass spectra, two or three fragmentation pathways for each compound are proposed. The consecutive losses of two H(2)O molecules and one H(2) molecule readily take place from the furan rings for both sesamin and gmelinol, resulting in the absence of the protonated molecules in the single-stage experiments. HCHO loss is observed at least three times in the tandem mass spectra, mainly from methylenedioxy groups (OCH(2)O) for sesamin but only from tetrahydrofuran rings for gmelinol. Moreover, CO loss is found at least three times in the tandem mass spectra of both sesamin and gmelinol from the 3,4-methylenedioxyphenyl (ArOCH(2)O) moieties for sesamin and from both the dimethoxyphenyl and the tetrahydrofuran ring moieties for gmelinol. In addition, the disubstituted benzyl cation ArCH(2)+ at m/z 135 for sesamin and at m/z 151 for gmelinol was found in the MS(3) spectra of both sesamin and gmelinol, which is very helpful in the identification of the compositions of 3,4-disubstituted groups on the benzene rings of the furofurans.