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1.
The products of the metastable decompositions of ionized ethyl formate (a) are characterized. The loss of water from a produces ·CH2CH2CO+, a rarely reported product. Loss of H appears to produce CH2=CHC(OH). The third decomposition is an unusual formation of C2H. This work demonstrates that a previous supposition that isomerization to different intermediates is involved in the losses of ethene and of water from a is correct.  相似文献   

2.
The Unimolecular mass spectrometric fragmentations of the molecular ions of 1,3-diphenylpropane, 1-(7-cycloheptatrienyl)-2-phenylethane and the 1-phenyl-2-tolylethanes and their [d5]phenyl analogues have been investigated by metastable ion techniques and measurements of ionization and appearance energies. By comparing the formation of [C7H7]+, [C7H8]+?, [C8H8]+? and [C8H9]+ it is shown that the molecular ions of the four diaryl isomers do not undergo ring expansion reactions of the aromatic nuclei prior to these fragmentations. Conversely, the molecular ions of the cycloheptatrienyl isomer suffer in part a contraction of the 7-membered ring. From these results and from the measured ionization and appearance energies lower limits to the activation energies of these skeletal isomerizations have been estimated yielding E > 33±5 kcal mol?1 formonoalkylbenzene, E > 20 2±5 kc mol?1 for 7-alkylcycloheptatriene and E > 40±5 kcal mol?1 for dialkylvbenzene positive radical ions. Upper limits can be deduced from literature evidence yielding E < 45 kcal mol?1 for monoalkylbenzene and E < 53 kcal 4mol?1 for dialkylbenzene positive radical ions. The activation energy thus estimated for monoalkylbenzene is in excellent agreement with the recently calculated value(s) for the toluene ion.  相似文献   

3.
The haloacetyl ions [XCH2CO+], X = Cl, Br, I, have been produced by the dissociative ionization of selected precursor molecules and identified via their fragmentation characteristics. Their heats of formation, Δ, were 708 ± 8, 750 ± 25 and 784 ± 10 kJ mol?1, respectively, all appreciably above ΔH for [CH3CO+], 653 kJ mol?1. The effect of halogen substitution α to carbonyl is discussed for neutral molecules and their molecular ions.  相似文献   

4.
The mass spectral fragmentation of twelve new 2-alkoxycarbonylalkylthio substituted derivatives of uracils is discussed and fragmentation pathways, elucidation of which were assisted by accurate mass measurements and metastable transitions are proposed. It has been found that the basic mass spectral fragmentation of these compounds is due to cleavage of S? C, O? C and C? C bonds of the alkoxycarbonylalkylthio group.  相似文献   

5.
Isomerization of oxime molecular ions into nitrone molecular ions upon electron impact does not generally occur, but it was established with the aid of deuterium labelling that it is essential for loss of CH from o-methylbenzaldoxime.  相似文献   

6.
Doubly charged molecular anions M2? of fullerenes are formed in the gas phase under chemical ionization conditions with isobutane as the reagent gas. The efficiency of double electron attachment increases with increasing size of the fullerenes: the C ion is the most abundant doubly charged anion in the negative-ion CI mass spectrum, although the concentration of C70 was about 12% in the fullerene mixture examined. Under low-energy collision-induced dissociation conditions an electron is ejected from the doubly charged C ion resulting in the singly charged molecular anion C˙. This process appears to be the first report of the ejection of an electron (electron stripping) from a doubly charged anion in the gas phase: .  相似文献   

7.
An ab initio LCAO-MO-SCF calculation was made on the proton affinity (PA ) of methylsilane (CH3SiH3) by using STO -3G, MIDI -1, and MIDI -1* basis sets. Three types of protonated methylsilane are taken into account, and their geometrical parameters are optimized. The calculated PA of CH3SiH3 is 160.5 kcal/mol, which exceeds that of SiH4 by 11.5 kcal/mol. The protonated species (I) which refers to Si—C bond protonation is shown to be most favorable, and to be a weak σ-complex between CH4 and SiH. Other two species are also σ-complexes between H2 molecule and SiH3CH or CH3SiH, and similar to CH, SiH, GeH, and C2H.  相似文献   

8.
A kinetic study has been made of the gas phase, I2-catalyzed decomposition of (CH3)2S at 630–650 K. Some I2 is consumed initially, reaching a steady-state concentration. The initial major products are CH4 and CH2S together with small amounts of CH3SCH2I, CH3I, HI, and CS2. The initial reaction corresponds to a pseudo-equilibrium: accompanied by: and which brings (I2) into steady state and a final complex reaction: From the initial rate of I2 loss it is possible to obtain Arrhenius parameters for the iodination: We measure k1, (644 K) = 150 L/mol s and from both the Arrhenius plot and independent estimates A1 (644 K) = 1011.2 ± 0.3 L/mol s. Thus, E1 = 26.7 ± 1 kcal/mol. From the steady-state I2 concentration, an assumed mechanism and the known rate parameters for the CH3I/HI system. It is possible to deduce KA (644) = 3.8 × 10?2 with an uncertainty of a factor of 2. Using an estimated ΔS (644) = 4.2 ± 1.0 e.u. we find ΔHA (644) = 7.0 ± 1.1 kcal. With 〈ΔCPA〉644 = 1.2 this becomes: ΔHA(298) = 6.6 ± 1.1 kcal/mol. Then ΔH (CH3SCH2I) = 6.3 ± 1 kcal/mol. Making the assumption that E?1 = 1.0 ± 0.5 kcal/mol we find ΔH (644) = 25.7 ± 0.7 kcal/mol and with 〈ΔCPI〉 = 1.2; ΔH = 25.3 ± 0.8 kcal/mol. This gives ΔH (CH3S?H2) = 35.6 ± 1.0 kcal/mol and DH (CH3SCH2? H) = 96.6 ± 1.0 kcal/mol. This then yields Eπ(CH2S) = 52 ± 3 kcal. From the observed rate of pressure increase in the system and the preceding data k3, is calculated for the step CH3SCH2 → CH3 + CH2S. From an estimated A-factor E3 is deduced and from the overall thermochemistry values for k?3 and E?3. A detailed mechanism is proposed for the I-atom catalyzed conversion of CH2S to CS2 + CH4.  相似文献   

9.
Ultraviolet absorption spectra have been characterized for the acetyl-h3 and acetyl-d3 radicals, which were generated by the flash photolysis of the corresponding acetones. The spectra are broad and intense, with values of the extinction coefficient at the respective maxima estimated as: ?CH3CO(215) = (1.0 ± 0.1) × 104 L/mol·cm and ?CD3CO(207.5) = (1.0 ± 0.05) × 104 L/mol·cm. Rate constants for the reactions of mutual interaction were estimated as: k = 3.5 × 1010 L/mol·s and k = 3.4 × 1010 L/mol·s. Rate constants for the reactions of cross interaction were estimated as: k = 8.6 × 1010 L/mol·s and k = 5.2 × 1010 L/mol·s. The related values of the cross interaction ratios k/(kk)1/2 = 2.6 and k/(kk)1/2 = 1.6 do not differ significantly from the statistical value of 2. The participation of the radical displacement reactions was estimated in terms of the fractions k/k = 0.38 and k/k = 0.47. Corroborative spectra were obtained from the flash photolysis of methyl ethyl ketone and biacetyl, and the relative rates of the competing primary processes were estimated from the relative peak heights of the acetyl and methyl radicals in each system.  相似文献   

10.
The unimolecular chemistry of the methyl carbamate radical cation, H2NCOOCH, 1, has been further investigated by a combination of mass spectrometry-based experiments (metastable ion (MI), collisional activation (CA), collision-induced dissociative ionization (CIDI), neutralization-reionization (NR) Spectrometry and 2H labelling) and ab initio molecular orbital calculations, executed at the MP3/6–31G*//4–31G level of theory and corrected for zero-point vibrational energies. Apart from the previously located maxima, i.e. H2NCOOCH3, 1, the distonic ion H2NC(OH)OCH3, 2, hydrogen-bridged ions [H2N? C?O…? H…?O?CH2], 5, and [H2N? CH?O…?…?H…?O?C? H], 7, there exist at least two other equilibrium structures, viz. the iminol ion H? N?C(OH)? OCH, la, and the hydrogen-bridged species [H2C?O…?H…?N(H)COH], 6a, which is closely related to ion 5. Although the iminol ion la lies only 30 kJ mol?1 above 1, our calculations indicate that the barriers for its formation either directly from ionized methyl carbamate 1 via a 1,3-hydrogen shift or indirectly via 1,4-hydrogen shifts from the distonic ion 2 are too high to allow the iminol ion to be involved in the unimolecular chemistry of ionized methyl carbamate. This explains the earlier observation that there are no H-D exchange reactions prior to decomposition of ionized labelled methyl carbamate, in contrast to the related ion methyl acetate. However, attempts to generate the iminol ion by loss of CH3CN from CH3CH?N? NHCOOCH3 produced the more stable distonic ion 2 instead, but it proved very difficult to assign its structure unequivocally because 2 can rapidly interconvert with 1 and so virtually identical dissociation characteristics ensue. Only by integration of results obtained from many experiments and from ab initio calculations could structure 2 be assigned. The distonic ion 2 can undergo two transformations: after stretching of the C? OCH2 bond the incipient formaldehyde can migrate within the electrostatic field of ionized hydroxyaminocarbene to the OH end to generate 5, but it can also migrate to the NH end to generate 6a. This explains the previous puzzling observation that H2NCOOCD forms both CD2OD· and CD2OH· in CA and NR experiments. The calculations and experiments indicate that, although the ion is exceedingly difficult to characterize, the distonic ion 2 is the key intermediate for all the observed dissociations of methyl carbamate.  相似文献   

11.
Ab initio molecular orbital theory with the STO -3G basis set is used to examine both charge and energy interactions in a series of meta- and para-substituted phenylborate anions and toluenes. Comparison of the results is made with data for substituted anilinium cations. It is concluded that whereas NH is a powerful σ acceptor, with essentially no π interaction, BH is primarily a π donor, and, to a slight extent only, a π donor. CH3 is indicated to be both a weak σ and π donor. Energies of interaction of BH and NH with a series of substituents are an order of magnitude larger than corresponding values for CH3. Interaction energies for BH are of opposite sign to those for NH. The results may be understood qualitatively using perturbation molecular orbital (PMO ) theory.  相似文献   

12.
63Cu-NMR.-Spectra of Cu(CH3CN)4X (X = ClO, BF, PF) and Cu(C5H5N)4X (X = ClO, BF) in solution are reported at different temperatures and concentrations. The influence of temperature on the linewidth and chemical shift indicates an equilibrium of Cu(CH3CN) and Cu(C5H5N) with another complex of lower symmetry. The preferential solvation of Cu (I) by pyridin in a mixture acetonitrile/pyridine is clearly shown.  相似文献   

13.
A Fourier transform ion cyclotron resonance study of the gas-phase reaction of W+ with allene is reported. W+ successively dehydrogenates at least nine allene molecules, leading to the formation of a series of WC3nH ions, with WC27H as the largest product observed after a reaction delay of 40 s. Starting from the third reaction, there is a competition between elimination of H2 and C2H2 at each step. The activation of propyne was also investigated and found to lead to essentially the same sequence as with allene. The reaction of W+ with 1,1-d2-allene and collision-induced dissociation spectra of product ions are used to discuss a plausible mechanism for the formation and structures of some of the species observed.  相似文献   

14.
Silaheterocycles. III. Synthesis and Reactivity of Di-tbutylneopentylsilaethene, Bu Si?CHCH2But The three di-tbutylvinylsilanes BuSi(X)CH?CH2 (X = H 5 , X = F 9 , X = Cl 22 ) are prepared by the reaction of their SiCl precursors with vinyl lithium. In the treatment with LiBut the first step is the generation of the α-lithio compound BuSi(X)CH(Li)CH2But, the following reactions are governed by the nature of the substituent X and the reaction conditions (solvent, concentration, temperature). For X = H 2,3-LiH elimination leads to BuSi(H)CH?CHBut ( 7 ), with X = F or Cl Si?C formation by 1,2-LiX elimination competes with intermolecular Si-C-coupling producing BuSi(H)CH(SiBuCH?CHBut)CH2But ( 13 ) as the main product. BuSi?CHCH2But ( 1 ) probably coordinates to LiBut and reacts to yield BuSiCH?CHBut ( 3 ) and 7 , forms tetrabutyl-dineopentyl-1,3-disilacyclobutane 2 by cyclodimerization and 13 by addition of BuSi(X)CH(Li)CH2But.  相似文献   

15.
Cationic polymerization of tetrahydrofuran (THF) in CH2Cl2 solvent and in mixed CH2Cl2/CH3NO2 solvent was initiated with 1,3-dioxolan-2-ylium cations with AsF and SbF anions. Dissociation constants of the polytetrahydrofuranium ion pairs into ions were measured (e.g., KD = 1.5 × 10?5M at 25°C and [THF]0 = 7.0M; CH2Cl2 solvent) and were found to be more than 100 times lower than in CH3NO2 solvent at the same [THF]0 and temperature. The rate constants k and k, measured for degrees of dissociation ranging from 0.03 to 0.35 in CH2Cl2, were the same within an experimental error of measurements (±15% of the value of kp). Dependence of k( = k = k) on the dielectric constant was a monotonous function in three different solvents, namely, CCl4, CH2Cl2, and CH3NO2, which covered a large range of dielectric constants of the medium (from D = 5 to D = 22) and degrees of dissociation of the macroion pairs, α (from 0.03 to more than 0.70). Thus a decrease in the dielectric constant increases the rate constant k in the whole range of studied polarities of the medium. This result confirms an earlier conclusion that the rate constant of propagation does not depend on the state of aggregation of ions and k = k.  相似文献   

16.
The mass spectra of a series of thirteen m- and p-substituted benzils have been determined at several ionising voltages below 20 eV and at 70 eV. At ionising voltages up to 5 eV above the ionisation potentials the benzil molecular ions decompose entirely by two pathways to give substituted and unsubstituted benzoyl ions. Fractional intensities of the molecular ion (FM), substituted (FX) and unsubstituted (FH) benzoyl ions were obtained for each benzil as a function of energy from measured ionisation efficiency curves, and ionisation and appearance potentials for all major ions determined from the ionisation efficiency curves by a semilogarithmic method. Various correlations of ion intensity and energy parameters with δ+ and δ constants are examined; these are generally poor. Fair correlations are obtained between log (FX/FH) or (AP – AP) and δ or δ+, and these are interpreted in terms of the expected effect of substituents on the stabilities of the product ions in the decompositions. A good correlation is observed between log (FX/FH) and AP · AP; this suggests that substituents affect FX/FH mainly by changing the activation energies for the competing decompositions of the molecular ions. The competitive shift has a marked effect on these appearance potentials so that in this system AP – IP is not a good measure of the activation energy for the primary decompositions.  相似文献   

17.
19F NMR Spectroscopic Evidence and Calculation of the Statistical Formation of Mixed Cluster Anions [(Mo6Br Cl )F ]2?, n = 0 – 8 The complete system of the innersphere mixed clusters (Mo6BrCl)4+ is formed by exchange of innersphere bound Cli against outersphere bound Bra on tempering the solid [(Mo6Cl)Br] at 500°C for 16 h. After conversion with conc. HCl into (H3O)2[(Mo6BrCl)Cl] and precipitation of the outer Cla with AgBF4 in ethanol, treatment with tetrabutylammonium(TBA)fluoride yields (TBA)2 [(Mo6BrCl)F], a mixture of 22 different species. According to the sets of chemical equivalent fluorine atoms in total 55 19F nmr signals are expected, which are really observed in the high resolution 1D-19F-nmr spectrum. Using increments of chemical shifts, peak intensities and multiplet structures as well as the 2D-19F/19F-COSY spectrum the complete and unambiguous assignment of all resonances is achieved. From the measured integral intensities the distribution of the different compounds is determined, revealing statistical formation of the geometrical isomers.  相似文献   

18.
Reactions of dry THF/MeCN solutions of Ca[Re6SCl(Cla)6] with silylated derivatives E(SiMe3)2 (E = PhAs, PSiMe3, HN, O, S) and addition of trialkylphosphine PPr3 afford in high yields and at room temperature either the neutral clusters [Re6SX(PPr3)] ( 1 : X = As, 2 : X = P) or the ionic compounds [Re6SX(PPr3)]2+ · [Re6S6Cl8]2– ( 3 : X = NH, 4 : X = O, 5 : X = S). The compounds 1 – 5 were characterised by X‐ray crystal structure analysis. A di‐substitution reaction occurs on the {Re6SCl}4+ cluster core, where the two inner μ3‐chloro ligands Cli are substituted by X (X = As, P, NH, O, S) and all six terminal chloro ligands Cla are exchanged by terminal PPr3‐ligands.  相似文献   

19.
The molecular structures of monocyclic sulfur-nitrogen ring systems, such as S2N2, S3N, S4N and S5N, can be considered as examples of electron rich (4n + 2)π systems. The structures of S4N4, S4N, P4S4, As4S4 and the bicyclic structures S4N, S4N as well as S5N6 can be rationalized on the basis of a planar tetrasulfur tetranitride with 12π electrons.  相似文献   

20.
Synthesis, Vibrational Spectra, and Crystal Structure of ( n ‐Bu4N)2[(W6Cl )F ] · 2 CH2Cl2 and 19F NMR Spectroscopic Evidence of the Mixed Cluster Anions [(W6Cl )F Cl ]2–, n = 1–6 The reaction of (n‐Bu4N)2[(W6Cl)Cl] with CF3COOH in dichloromethane gives intermediately a mixture of the cluster anions [(W6Cl)(CF3COO)Cl]2–, n = 1–6. By treatment with NH4F the outer sphere coordinated trifluoracetato ligands are easily substituted and the components of the series [(W6Cl)FCl], n = 1–6 are formed and characterized by their distinct 19F NMR chemical shifts. An X‐ray structure determination has been performed on a single crystal of (n‐Bu4N)2[(W6Cl)F] · 2 CH2Cl2 (orthorhombic, space group Pbca, a = 15.628(4), b = 17.656(3), c = 20.687(4) Å, Z = 4). The low temperatur IR (60 K) and Raman (20 K) spectra are assigned by normal coordinate analysis based on the molecular parameters of the X‐ray determination. The valence force constants are fd(WW) = 1.89, fd(WF) = 2.43 and fd(WCl) = 0.93 mdyn/Å.  相似文献   

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