Cross Conjugated Polyenes Derived from 2-Vinyl-butadiene: Electronic States of their Radical Cations,and Triplet Energy

The doublet states of the radical cations of the cross conjugated polyenes 4,4-dimethyl-1-methylidene-2,5-cyclohexadiene 2 and its bis-derivative 1 have been investigated by photoelectron spectroscopy and by electronic spectroscopy of \documentclass{article}\pagestyle{empty}\begin{document}$ \rm {1}^{+\kern-4pt {.} } $\end{document}⁺, prepared at 77 K in an electron scavenging matrix by γ-irradiation. Simultaneous consideration of the spectral results shows \documentclass{article}\pagestyle{empty}\begin{document}$ \rm {1}^{+\kern-4pt {.} } $\end{document} to be the second hydrocarbon molecular cation (after 2,2-dimethyl isoindene) which possesses a first excited doublet state (D₁) of non-Koopmans nature (²B_3g). The first Koopmans-type excited state (²B_2g) expected from PE. spectroscopy lies, however, very close in energy. In addition T₁ of 1 was observed by electron energy loss spectroscopy at 2.0±0.1 eV. Application of the ‘SDT-equation’ predicts for this state only 1.05 eV; there is at present no reasonable explanation for this failure.     

Three new isomers of [C2H6O]+˙: The radical cations [CH3O(H)CH2]+˙, [CH3CHOH2]+˙ and a low-energy isomer of unassigned structure

Three new [C₂H₆O]⁺˙ ions have been generated in the gas phase by appropriate dissociative ionizations and characterized by means of their metastable and collisionally induced fragmentations. The heats of formation, ΔH_f⁰, of the two ions which were assigned the structures [CH₃O(H)CH₂]⁺˙ and [CH₃CHOH₂]⁺˙ could not be measured. The third isomer, to which the structure \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 2} = \mathop {\rm C}\limits^{\rm .} {\rm H} \cdot \cdot \cdot \mathop {\rm H}\limits^ + \cdot \cdot \cdot {\rm OH}_{\rm 2} $\end{document} is tentatively assigned, was measured to have ΔH_f⁰ = 732±5 kJ mol^?1, making it the [C₂H₆O]⁺˙ isomer of lowest experimental heat of formation. It was found that the exothermic ion–radical recombinations [CH₂OH]⁺+CH₃˙→[CH₃O(H)CH₂]⁺˙ and \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 3} \mathop {\rm C}\limits^{\rm + } {\rm HOH + H}^{\rm .} $\end{document}→[CH₃CHOH₂]⁺˙ have large energy barriers, 1.4 and ?0.9 eV, respectively, whereas the recombinations yielding [CH₃CH₂OH]⁺˙ have little or none.     

An investigation of the decomposition of the intermediate ions produced by electron-impact. II—[C7H7]+ ions from several halogenotoluenes

The structure and decomposition of the [C₇H₇]⁺ ions produced by electron-impact from o-, m- and p-chlorotoluene, o-, m- and p-bromotoluence, and p-iodotoluence, have been investigated. By determining the relative abundance of normal and metastable ions, these [C₇H₇]⁺ ions at electron energy of 20 eV are shown to be so-called ‘tropylium ions’. The amount of the internal energy of the [C₇H₇]⁺ ion estimated by the relative ion abundance ratios, ? [C₅H₅]⁺/[C₇H₇]⁺ and m*/[C₇H₇]⁺ for the decomposition \documentclass{article}\pagestyle{empty}\begin{document}$ [{\rm C}_{\rm 7} {\rm H}_{\rm 7}]^ + \mathop \to \limits^{m^* } [{\rm C}_{\rm 5} {\rm H}_{\rm 5}]^ + + {\rm C}_{\rm 2} {\rm H}_{\rm 2} $\end{document}, is in the order iodotoluene > bromotoluene > chlorotoluene. The heats of formation of the activated complexes for the reaction \documentclass{article}\pagestyle{empty}\begin{document}$ [{\rm C}_{\rm 7} {\rm H}_{\rm 7}]^ + \mathop \to \limits^{m^* } [{\rm C}_{\rm 5} {\rm H}_{\rm 5}]^ + + {\rm C}_{\rm 2} {\rm H}_{\rm 2} $\end{document} were estimated. The values suggest that the decomposing [C₇H₇]⁺ ions from various halogenotoluenes are identical in structure.     

Hydrogen migrations in mass spectrometry. III–Energetics of formation of [R′CO2H2]+ in the mass spectra of R′CO2R

The appearance potentials for the [R'CO₂H₂]⁺ ion produced in the fragmentation process \documentclass{article}\pagestyle{empty}\begin{document}$ \left[{{\rm R}^{\rm '} {\rm CO}_{\rm 2} {\rm R}} \right]_{}^{_.^ + } $\end{document} → [R'CO₂H₂]⁺+[R? 2H] have been measured using mono-energetic electron impact techniques for ethyl, n-propyl, and i-propyl formates and acetates. The results indicate that at the threshold the product ion has the protonated acid structure with the hydrogen on the carbonyl and not the hydroxyl group, and that the neutral product for the propyl esters is the allyl radical and not the cyclopropyl radical. For the propyl formates and acetates the appearance potential of the [R'CO₂H₂]⁺ ion is identical with the adiabatic ionization potential of the parent ester (measured by photoelectron spectroscopy) indicating that fragmentation occurs for ground state molecular ions. A two-step mechanism is proposed to rationalize the results.     

The gas-phase pyrolysis of alkyl nitrites. III. Isopropyl nitrite

The rate of decomposition of isopropyl nitrite (IPN) has been studied in a static system over the temperature range of 130–160°C. For low concentrations of IPN (1–5 × 10^?5M), but with a high total pressure of CF₄ (～0.9 atm) and small extents of reaction (～1%), the first-order rates of acetaldehyde (AcH) formation are a direct measure of reaction (1), since k₃ » k₂(NO): \documentclass{article}\usepackage{amssymb}\pagestyle{empty}\begin{document}$ {\rm IPN}\begin{array}{rcl} 1 \\ {\rightleftarrows} \\ 2 \\ \end{array}i - \Pr \mathop {\rm O}\limits^. + {\rm NO},i - \Pr \mathop {\rm O}\limits^. \stackrel{3}{\longrightarrow} {\rm AcH} + {\rm Me}. $\end{document} Addition of large amounts of NO (～0.9 atm) in place of CF₄ almost completely suppressed AcH formation. Addition of large amounts of isobutane – t-BuH – (～0.9 atm) in place of CF₄ at 160°C resulted in decreasing the AcH by 25%. Thus 25% of \documentclass{article}\pagestyle{empty}\begin{document}$ i - \Pr \mathop {\rm O}\limits^{\rm .} $\end{document} were trapped by the t-BuH (4): \documentclass{article}\pagestyle{empty}\begin{document}$ i - \Pr \mathop {\rm O}\limits^. + t - {\rm BuH} \stackrel{4}{\longrightarrow} i - \Pr {\rm OH} + (t - {\rm Bu}). $\end{document} The result of adding either NO or t-BuH shows that reaction (1) is the only route for the production of AcH. The rate constant for reaction (1) is given by k₁ = 10^{16.2±0.4–41.0±0.8}/θ sec^?1. Since (E₁ + RT) and ΔH°₁ are identical, within experimental error, both may be equated with D(i-PrO-NO) = 41.6 ± 0.8 kcal/mol and E₂ = 0 ± 0.8 kcal/mol. The thermochemistry leads to the result that \documentclass{article}\pagestyle{empty}\begin{document}$ \Delta H_f^\circ (i - {\rm Pr}\mathop {\rm O}\limits^{\rm .} ) = - 11.9 \pm 0.8{\rm kcal}/{\rm mol}. $\end{document} From ΔS°₁ and A₁, k₂ is calculated to be 10^10.5±0.4M^?1·sec^?1. From an independent observation that k₆/k₂ = 0.19 ± 0.03 independent of temperature we find E₆ = 0 ± 1 kcal/mol and k₆ = 10^9.8+0.4M^?;1·sec^?1: \documentclass{article}\pagestyle{empty}\begin{document}$ i - \Pr \mathop {\rm O}\limits^. + {\rm NO} \stackrel{6}{\longrightarrow} {\rm M}_2 {\rm K} + {\rm HNO}. $\end{document} In addition to AcH, acetone (M₂K) and isopropyl alcohol (IPA) are produced in approximately equal amounts. The rate of M₂K formation is markedly affected by the ratio S/V of different reaction vessels. It is concluded that the M₂K arises as the result of a heterogeneous elimination of HNO from IPN. In a spherical reaction vessel the first-order rate of M₂K formation is given by k₅ = 10^9.4–27.0/θ sec^?1: \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm IPN} \stackrel{5}{\longrightarrow} {\rm M}_2 {\rm K} + {\rm HNO}. $\end{document} IPA is thought to arise via the hydrolysis of IPN, the water being formed from HNO. This elimination process explains previous erroneous results for IPN.     

Mass spectrometry of organic compounds of the group V Elements: VI—A new type of amine fragmentation under electron impact

A new type of amine fragmentation under electron impact is elucidated for proline, sarcosine and aspartic acid derivatives and aminomethylphosphines of the general formula R₂NCH₂X. Ordinary α-cleavage affording the \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm R}_2 \mathop {\rm N}\limits^{\rm + } {\rm = CH}_{\rm 2} $\end{document} ion is suppressed by elimination of a neutral HX particle and [M - HX]⁺ ion formation, or M-HX neutral particle ejection and generation of an [HX]⁺ ion from [M]⁺˙. Such fragmentation is ensured by the presence of an α-heteroatom (N, O, P, S) in one substituent (X) and a CO₂R type delocalizing group in the α-position of the other substituent (R₂N).     

Pyrolysis of dimethyl peroxide

By using isobutane (t-BuH) as a radical trapit has been possible to study the initial step in the decomposition of dimethyl peroxide (DMP) over the temperature range of 110–140°C in a static system. For low concentrations of DMP (2.5 × 10^?5?10^?4M) and high pressures of t?BuH (～0.9 atm) the first-order homogeneous rate of formation of methanol (MeOH) is a direct measure of reaction (1): \documentclass{article}\pagestyle{empty}\begin{document}${\rm DMP}\mathop \to \limits^1 2{\rm Me}\mathop {\rm O}\limits^{\rm .},{\rm Me}\mathop {\rm O}\limits^{\rm .} + t{\rm - BuH}\mathop \to \limits^4 {\rm MeOH} + t{\rm -}\mathop {\rm B}\limits^{\rm .} {\rm u}$\end{document}. For complete decomposition of DMP in t-BuH, virtually all of the DMP is converted to MeOH. Thus DMP is a clean thermal source of Me\documentclass{article}\pagestyle{empty}\begin{document}$\mathop {\rm O}\limits^{\rm .}$\end{document}. In the decomposition of pure DMP complications arise due to the H-abstraction reactions of Me\documentclass{article}\pagestyle{empty}\begin{document}$\mathop {\rm O}\limits^{\rm .}$\end{document} from DMP and the product CH₂O. The rate constant for reaction (1) is given by k₁ = 10^15.5?37.0/θ sec^?1, very similar to other dialkyl peroxides. The thermochemistry leads to the result D(MeO? OMe) = 37.6 ± 0.2 kcal/mole and /H(Me\documentclass{article}\pagestyle{empty}\begin{document}$\mathop {\rm O}\limits^{\rm .}$\end{document}) = 3.8 ± 0.2 kcal/mole. It is concluded that D(RO? OR) and D(RO? H) are unaffected by the nature of R. From ΔS and A₁, k₂ is calculated to be 10^10.3±0.5 M^?1· sec^?1: \documentclass{article}\pagestyle{empty}\begin{document}$2{\rm Me}\mathop {\rm O}\limits^{\rm .} \mathop \to \limits^2 {\rm DMP}$\end{document}. For complete reaction, trace amounts of t-BuOMe lead to the result k₂ ～ 10⁹ M^?1 ·sec^?1: \documentclass{article}\pagestyle{empty}\begin{document}$2t{\rm - Bu}\mathop \to \limits^5$\end{document} products. From the relationship k₆ = 2(k₂k_5a)^1/2 and with k_5a = 10^8.4 M^?1 · sec^?1, we arrive at the result k₆ = 10^9.7 M^?1 · sec^?1: \documentclass{article}\pagestyle{empty}\begin{document}$2t{\rm - u}\mathop {\rm B}\limits^{\rm .} \to (t{\rm - Bu)}_{\rm 2}{\rm,}t{\rm -}\mathop {\rm B}\limits^{\rm .} {\rm u} + {\rm Me}\mathop {\rm O}\limits^{\rm .} \mathop \to \limits^6 t{\rm - BuOMe}$\end{document}.     

Laser-induced chemical kinetics: Absolute rate constants for the reactions Ċ2F2 + Br2 → C2F5Br + Ḃr and n-Ċ3F7 + Br2 → n-C3F7Br + Ḃr

Absolute rate constants at room temperature for the metathesis reaction have been measured under VLPP conditions: k₁ = (2.0 ± 0.5) × 10⁸M^?1·s^?1, k₂ = (3.0 ± 0.7) × 10⁸M^?1·s^?1. The radicals were generated through collisionless infrared-multiphoton decomposition of the corresponding iodides by irradiation from a high-power CO₂-TEA laser. The reaction of ?₂F₅ and ?₃F₇ with \documentclass{article}\pagestyle{empty}\begin{document}$$\mathop {\rm N}\limits^{\rm .} {\rm O}_{\rm 2} $$\end{document} are briefly discussed in relation to the reaction of ?₃ with \documentclass{article}\pagestyle{empty}\begin{document}$$\mathop {\rm N}\limits^{\rm .} {\rm O}_{\rm 2} $$\end{document}, which had been measured previously.     

Structure and formation of gaseous [C4H5O]+ Ions. II–Ions of the type HCC?\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document}(OH)(CH3)

Loss of an alkyl group X? from acetylenic alcohols HC?C? CX(OH)(CH₃) and gas phase protonation of HC?C? CO? CH₃ are both shown to yield stable HC?C? \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document}(OH)(CH₃) ions. Ions of this structure are unique among all other [C₄H₅O]⁺ isomers by having m/z 43 [C₂H₃O]⁺ as base peak in both the metastable ion and collisional activation spectra. It is concluded that the composite metastable peak for formation of m/z 43 corresponds to two distinct reaction profiles which lead to the same product ion, CH₃\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document}?O, and neutral, HC?CH. It is further shown that the [C₄H₅O]⁺ ions from related alcohols (like HC?C? CH(OH)(CH₃)) which have an α-H atom available for isomerization into energy rich allenyl type molecular ions, consist of a second stable structure, H₂C?\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document}? C(OH)?CH₂.     

[C3H3O]+ ions; reacting and non-reacting configurations

Three [C₃H₃O]⁺ ion structures have been characterized. The most stable of these is \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 2} = {\rm CH} - \mathop {\rm C}\limits^ + = {\rm O} $\end{document} its heat of formation ΔH_f was measured as 749±5 kJ mol^?1. In the μs time frame this ion fragments exclusively by loss of CO, a process which also dominates its collisional activation mass spectrum. The other stable [C₃H₃O]⁺ structures, \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}\equiv \mathop {\rm C}\limits^ + - {\rm CHOH} $\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 2} = {\rm C} = \mathop {\rm C}\limits^{\rm + } - {\rm OH}, $\end{document}, were generated from some acetylenic and allenic precursor ions; their heats of formation were estimated to be 830 and 880 kJ mol^?1 respectively. The former ion was also produced by the gas phase protonation of propynal. These ions show loss of C₂H₂ and CO in both their metastable ion and collisional activation mass spectra. The broad Gaussian-type metastable peak for the loss of CO was shown to consist of two components corresponding to gragmentations having different activation energies.     

Neutral counterparts of the C2H7O+ isomers

The neutral counterparts of the C₂H₇O⁺ isomers CH₃O⁺ (H)CH₃, CH₃CH₂OH₂⁺ and $ {\rm C}_2 \,{\rm H}_4 \,\, \cdot \cdot \cdot \mathop {\rm H}\limits^ + \, \cdot \cdot \cdot {\rm OH}_2 $ were studied by neutralization-reionization mass spectrometry. Protonated dimethyl ether and its —O(D)⁺ analogue were produced by protonation (deuteration) of dimethyl ether and also generated as a fragment ion from (labeled) ionized CH₃OCH₂CH(OH)CH₃ by loss of CH₃CO?. It was observed that the dissociation characteristics of the ions and the stability of their neutral counterpart depended on the internal energy of the protonated ether ions. Stable neutral CH₃?(H)CH₃ was only produced from energy-rich ions. The classical protonated ethanol ion CH₃CH₂OH₂⁺ (a) was produced at threshold by the loss of CH₃CO?. from ionized butane-2,3-diol. Mixtures of a with the non-classical ion $ {\rm C}_2 \,{\rm H}_4 \,\, \cdot \cdot \cdot \mathop {\rm H}\limits^ + \, \cdot \cdot \cdot {\rm OH}_2 $ (b) were produced by reaction of C₂H₅⁺ ions with H₂O. As for the protonated ether, only high-energy a and/or b ions yielded stable hypervalent radicals. It is suggested that the stable C₂H₇?O radicals are Rydberg states.     

The kinetics of the bromate–sulfite reaction system

The kinetics of the reaction between BrO₃⁻ and sulfite was studied by measuring the concentrations of [Br⁻] and [H⁺] both in buffered and in unbuffered solutions. A mechanism was applied for simulation of the experimental observations. Rate constants k₁=(0.027±0.004) M⁻¹s⁻¹ and k₂=(85±5) M⁻¹s⁻¹ were determined for the following reactions: \halign{\hfill $#$\hfill &\hfill\qquad\qquad #\cr 3\ \rm HSO_{3}\!^{-}+BrO_{3}\!^{-}\longrightarrow 3\ SO_{4}\!^{2-}+Br^{-}+3\ H^{+}& (1)\cr 3\ \rm H_{2}SO_{3}(\hbox{or}\ SO_{2.}\hbox{aq})+BrO_{3}\!^{-}\longrightarrow 3\ SO_{4}\!^{2-}+Br^{-}+6\ H^{+}& (2)\cr } Rate constant k₁ was obtained directly from the experimental results on unbuffered reactions, where Reaction (1) was predominant. Rate constant k₂ was obtained by computer fitting of [Br⁻] to the experimental values for buffered reactions, where the rate of Reaction (2) was about four times higher than that of Reaction (1). © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 869–874, 1998     

The collisionally induced dissociation of allyl and 2-propenyl cations

Pure [CH₂CHCH₂]⁺ and \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm{CH}}_{\rm{3}} \mathop {\rm{C}}\limits^{\rm{ + }} = {\rm{CH}}_{\rm{2}} $\end{document} ions are generated only in metastable fragmentations of [CH₂?CHCH₂X]⁺˙, X=Cl, Br, I, and [CH₃CX?CH₂]⁺˙, X=Br, I, respectively. For ion source generated [C₃H₅]⁺ ions there is some structural interconversion. The structure characteristic feature of their collisional activation mass spectra is the ratio m/z 27 ([C₂H₃]⁺): m/z 26 ([C₂H₂]⁺˙). For \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm{CH}}_{\rm{3}} \mathop {\rm{C}}\limits^{\rm{ + }} = {\rm{CH}}_{\rm{2}} $\end{document} the ratio is only weakly dependent upon the translational energy of the ion. For [CH₂CHCH₂]⁺, the ratio rises sharply as translational energy is reduced, from 0.9 at 8 kV to c. 3 at 1 kV. [CH₂CHCH₂]⁺ ions generated by charge reversal of [CH₂CHCH₂]^? show higher ratios, resulting from their lower average internal energy content. It must therefore be emphasized that [C₃H₅]⁺ ion structure assignments should only be made using reference data which apply to specific experimental conditions. [C₃H₅]⁺ daughter ion structures for a number of well-known fragmentations have been established. The heat of formation of the 2-propenyl cation was measured to be 969±5 kJ mol^?1. Labelling experiments show that at low internal energies, allyl cations do not undergo atom randomization in c. 1–2 μs; high internal energy ions of longer lifetime (c. 8 μs) show complete atom randomization. H^˙ atom loss from [¹³CH₃CH?CH₂]⁺˙ has been shown to generate [¹³CH₂CHCH₂]⁺ and \documentclass{article}\pagestyle{empty}\begin{document}$ {}^{{\rm{13}}}{\rm{CH}}_{\rm{2}} \mathop {\rm{C}}\limits^{\rm{ + }} - {\rm{CH}}_{\rm{3}} $\end{document} without any skeletal rearrangement.     

The mass spectra of six fluorinated β-diketones and their monothio analogues

The mass spectra of the fluorinated β-diketones RCOCH₂COCF₃ (R = Ph, p-FC₆H₄, p-ClC₆H₄, p-BrC₆H₄, p-MeC₆H₄ and 2-thienyl) and their monothio analogues RC(SH)?CHCOCF₃ have been obtained. The replacement of one oxygen by sulphur in the β-diketones brings about a greater complexity in the mass spectra. The β-diketones fragment by first losing a ·CF₃ radical and then successively lose CH₂?C?O and CO to yield \documentclass{article}\pagestyle{empty}\begin{document}${\rm [R}\mathop {\rm C}\limits^{\rm + } {\rm = O]} $\end{document} and [R]⁺. The monothio-β-diketones also fragment by an analogous reaction pathway: viz. the initial loss of ·CF₃ is followed by the successive loss of CH₂?C?O and CS to yield \documentclass{article}\pagestyle{empty}\begin{document}${\rm [R}\mathop {\rm C}\limits^{\rm + } {\rm = S]} $\end{document} and [R]⁺. However, they also fragment by two other pathways involving the initial loss of ·H and ·X (X=F, Cl, Br, Me), the latter occurring only with those monothio-β-diketones having R=p-XC₆H₄.     

Reaction of carbon monoxide with ozone: Kinetics and chemiluminescence

The reaction of carbon monoxide with ozone was studied in the range of 75–160°C in the presence of varying amounts of CO₂ and, for a few experiments, of O₂. At room temperature the reaction was immeasurably slow, but in a flow system it showed chemiluminescence with undamped oscillations. In a static system above 75°C the emission showed damped oscillations when O₂ was present. In the absence ofadded O₂ the emission showed a slow decay with a half-life of 1 hr. The luminescence consisted of partially resolved bands in the range of 325–600 nm, and the source was identified as CO₂(¹B₂) → CO₂(¹Σ_g⁺) + hv. The kinetics were complex, and the observed rate law could be accounted for bya mechanism involving the chain sequence \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm O(}^{\rm 3} P{\rm ) + CO( + M)}\mathop {{\rm rightarrow}}\limits^{\rm 3} {\rm CO}_{\rm 2} {\rm (}^{\rm 3} B_{\rm 2} {\rm ) ( + M), CO}_{\rm 2} {\rm (}^{\rm 3} B_{\rm 2} {\rm ) + O}_{\rm 3} {\rm }\mathop {{\rm rightarrow}}\limits^{\rm 7} {\rm CO}_{\rm 2} {\rm (}^{\rm 1} \sum\nolimits_{\rm g}^{\rm + } {} {\rm ) + O}_{\rm 2} {\rm + O} $\end{document}. From measurements of -d[O₃]/dtand relative emission, rate constant ratios were obtained and estimates of k₃were made.     

Methyl thiirane: Kinetic gas-phase titration of sulfur atoms in SX OY systems

The reaction SO + SO →l S + SO₂(2) was studied in the gas phase by using methyl thiirane as a titrant for sulfur atoms. By monitoring the C₃H₆ produced in the reaction \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm S} + {\rm CH}_3\hbox{---} \overline {{\rm CH\hbox{---}CH}_2\hbox{---} {\rm S}} \to {\rm S}_2 + {\rm C}_3 {\rm H}_6 (7) $\end{document}, we determined that k₂ ? 3.5 × 10^?15 cm³/s at 298 K.     

Rate constants for the reactions of molecular iodine with Cl,SiCl3, and SiH3 at 298 K

Rate constants k₁, k₂, and k₃ have been measured at 298 K by means of a laser photolysis-laser magnetic resonance technique and (or) by a laser photolysis-infrared chemiluminescence detection technique (LMR and IRCL, respectively). \hfill\hbox to 12em{$\rm Cl+I_2\longrightarrow ICl+I;$}\hbox to 8em{$\rm {\it k}_1=(2.5\pm 0.7)\times 10^{-10}(IRCL)$}\hfill(1)\\\hfill\hbox to 12em{}\hbox to 8em{$\rm {\it k}_1=(2.8\pm 0.8)\times 10^{-10}(LMR)$}\hfill \\\hfill\hbox to 12em{$\rm SiCl_3+I_2\longrightarrow SiCl_3I+I;$}\hbox to 8em{$\rm {\it k}_2=(5.8\pm 1.8)\times 10^{-10}(IRCL)$}\hfill (2)\\\hfill\hbox to 12em{$\rm SiH_3+I_2\longrightarrow SiIH_3+I;$}\hbox to 8em{$\rm {\it k}_3=(1.8\pm 0.46)\times 10^{-10}(LMR)$}\hfill (3)\\ As an average of the LMR and IRCL results we offer the value k₁ = (2.7 ± 0.6) × 10⁻¹⁰. Units are cm³ molecule⁻¹ s⁻¹; uncertainties are 2σ including precision and estimated systematic errors. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 25–33, 1997.     

Polymerization of σ-bonded organo-transition metal derivatives of styrene

Five new monomers of transition metal complexes containing a styryl group, trans-\documentclass{article}\pagestyle{empty}\begin{document}$ {\rm Pd}({\rm PBu}_{\rm 3})_2 \rlap{--} ({\rm C}_6 {\rm H}_4 {\rm CH} \hbox{=\hskip-2pt=} {\rm CH}_2 ){\rm X\ X \hbox{=\hskip-2pt=} Cl(Ia),\ X \hbox{=\hskip-2pt=} Br(Ib)},\ {\rm X \hbox{=\hskip-2pt=} CN(Ic),\ X \hbox{=\hskip-2pt=} Ph(Id)} $\end{document} and trans-\documentclass{article}\pagestyle{empty}\begin{document}${\rm Pt(PBu}_{\rm 3} {\rm )}_{\rm 2} \rlap{--} ({\rm C}_{\rm 6} {\rm H}_{\rm 4} {\rm CH} \hbox{=\hskip-2pt=} {\rm CH}_2 ){\rm Cl}({\rm II})$\end{document}, were synthesized. The monomers were readily homopolymerized in benzene with the use of AIBN or BBu₃–oxygen as the initiator. Copolymerization of Ia with styrene was carried out by using AIBN. From the Cl content of the copolymers by analysis, monomer reactivity ratios and Q–e values were obtained as follows: r₁ = 1.49, r₂ = 0.45; Q₂ = 0.41, e₂ = ?1.4 (M₁ = styrene, M₂ = Ia). Based on the above data, the σ-bonded palladium moiety at para position of styrene acts as a strongly electron-donating group to the phenyl ring. This is also supported by the olefinic β-carbon chemical shift of ¹³C NMR for Ia.     

Loss of methyl radical from some small immonium ions: Unusual violation of the even-electron rule

Several small immonium ions of general formula \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm R}^{\rm 1} {\rm R}^{\rm 2} {\rm C = }\mathop {\rm N}\limits^{\rm + } {\rm R}^{\rm 3} {\rm CH}_{\rm 3} $\end{document} (R¹, R², R³ = H or alkyl) eliminate ^.CH₃; this reaction occurs in the mass spectrometer in both fast (source) and slow (metastable) dissociations. Such behaviour violates the even-electron rule, which states that closed-shell cations usually decompose to give closed-shell daughter ions and neutral molecules. The heats of formation of the observed product ions (for example, [(CH₃)₂C?NH]^+.) can be bracketed using arguments based on energy data. Deuterium labelling results reveal that the methyl group originally bound to nitrogen is not necessarily lost in the course of dissociation. Thus, for instance, \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm{(CH}}_{\rm{3}})_2 = \mathop {\rm{N}}\limits^{\rm{ + }} {\rm{HCD}}_{\rm{3}} $\end{document} eliminates both CH₃^. and CD₃^., via different mechanisms, but very little CH₂D^. or CHD₂^. loss occurs.     

Structures and relative energies of gas-phase [C2H7N]+˙ radical cations

Ab initio molecular orbital calculations with split-valence plus polarization basis sets and incorporating electron correlation and zero-point energy corrections have been used to examine possible equilibrium structures on the [C₂H₇N]⁺˙ surface. In addition to the radical cations of ethylamine and dimethylamine, three other isomers were found which have comparable energy, but which have no stable neutral counterparts. These are \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm .} {\rm H}_{\rm 2} {\rm CH}_{\rm 2} \mathop {\rm N}\limits^{\rm + } {\rm H}_{\rm 3} $\end{document}, \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 3} \mathop {\rm C}\limits^{\rm .} {\rm H}\mathop {\rm N}\limits^{\rm + } {\rm H}_{\rm 3} $\end{document}and\documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 3} \mathop {\rm N}\limits^{\rm + } {\rm H}_{\rm 2} \mathop {\rm C}\limits^. {\rm H}_{\rm 2} {\rm }, $\end{document} with calculated energies relative to the ethylamine radical cation of ?33, ?28 and 4 kJ mol^?1, respectively. Substantial barriers for rearrangement among the various isomers and significant binding energies with respect to possible fragmentation products are found. The predictions for \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^. {\rm H}_{\rm 2} {\rm CH}_{\rm 2} \mathop {\rm N}\limits^ + {\rm H}_{\rm 3} $\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 3} \mathop {\rm C}\limits^{\rm .} {\rm H}\mathop {\rm N}\limits^{\rm + } {\rm H}_{\rm 3}$\end{document} are consistent with their recent observation in the gas phase. The remaining isomer, \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 3} \mathop {\rm N}\limits^{\rm + } {\rm H}_{\rm 2} \mathop {\rm C}\limits^{\rm .} {\rm H}_{\rm 2} {\rm },$\end{document}is also predicted to be experimentally observable.