CH3O(X2E) production from 266 nm photolysis of methyl nitrite and reaction with NO

The CH₃O($\text{X}$²E) radical produced by the 266 nm photolysis of CH₃ONO is characterized by laser-induced fluorescence. Using a flowing gas cell the reaction rate of CH₃O($\text{X}$²E) with NO is measured to be (2.08 ± 0.12) × 10^?11 cm³ s^?1 molecule^?1 based upon disappearance of CH₃O and appearance of HNO detected by laser induced fluorescence. Upper limits for CH₃O reactions with CH₄, CO, N₂O, NH₃, CH₃OH, (CH₃)₃CH and CH₂CHCH₂CH₃ are reported. These reactions are all too slow to measure under our experimental conditions.     

Photodecomposition of selenosulfonates and their facile photoaddition to alkenes 1

Phenyl areneselenosulfonates ($\text{1}$) are very photosensitive and easily undergo photodecomposition via initial homolysis of the SeS bond. In the presence alkenes this facile photodissociation of $\text{1}$ can be used to initiate a free radical chain reaction (eq 6) that leads to addition of $\text{1}$ to the alkene to form β-phenylselenosulfones ($\text{2}$). The photoaddition requires much shorter reaction times than the non-photolytic addition of $\text{1}$ to alkenes described recently.²     

The invention of new radical chain reactions. Part VIII. Radical chemistry of thiohydroxamic esters; A new method for the generation of carbon radicals from carboxylic acids

The aliphatic and alicyclic esters of N-hydroxypyridine-2-thione are readily reduced by tributylstannane in a radical chain reaction to furnish nor-alkanes.¹ In the absence of the stannane a smooth decarboxylatlive rearrangement occurs to give 2-substituted thiopyridines.¹ The radicals present in this reaction provoke with $\text{t}$-butylthiol an efficient radical reaction with formation of nor-alkane and 2-pyridyl-$\text{t}$-butyl disulphide.¹Similarly these carbon radicals can be captured by halogen atom transfer to give noralkyl chlorides, bromides and iodides. 2 With oxygen in the presence of t-butylthiol the corresponding noralkyl hydroperoxides are formed in another radical chain reaction.³     

Reactive scattering of O(1D) + H2

The angular and velocity distribution of OH product frorn the O(¹ D) + H₂ reaction at 2.7 $\text{kcal}\text{mole}$ collision energy has been obtained in a crossed molecular beam study. The product is found to be forward-backward symmetric; most of the reaction occurs through insertion of the oxygen to form ground electronic state H₂O.     

Alkali metal solutions. Effect of cryptands on solubility and spectra in tetrahydrofuran,dioxane and toluene

By use of alkali cation complexing agents of the cryptand type, alkalimetals solutions can be prepared which contain different species depending on the nature of the solvent. In THF, in the presence of cryptand, M^? and E^?_solv have been observed, and quantitative values of the molar extinction coefficients, the temperature coefficients ($\text{dν}\text{d}\text{t}$, $\text{d?}\text{d}\text{t}$) and the oscillator strength (f) have been determined. In dioxane alone, only cesium gives a blue solution (Cs^?); in the presence of cryptand, Na, K, Rb and Cs dissolve well, but only the M^? absorption is observed.In toluene, the metals are normally insoluble and a cation complexing agent is required to dissolve them; in all the examined cases the addition of cryptand tended to give an aromatic radical anion. Blue solutions are obtained only for Na; in that case the solution exhibits ESR and optical behavior which indicates the presence of both anion radical and M^?.     

Electron spin resonance spectra of some phosphonyl radicals and related species

The isotropic ESR spectra of a number of phosphonyl radicals (X₂$\text{P}$O), the dimethylphosphinyl radical, and the phosphoranyl radical (MeO)₃$\text{P}$OBu-t, are described, and accurate values of the phosphorus hyperfine splittings and g-factors are reported. For X₂$\text{P}$O, the value of a(P) increases and the g-factor decreases as the electronegativity of X increases. There is a linear relationship between a(P) for X₂$\text{P}$O and ¹J(PH) for X₂P(O)H, but the same relationship does not hold for Me₂P- and Me₂PH. The spectrum of the di-n-hexylphosphonyl radical shows coupling to two pairs of α-methylene protons, and this non-equivalence is attributed to the pyramidal structure of the phosphonyl radical.     

EPR Spectrum of Kr2F

An intense EPR spectrum observed in UV-irradiated solid Kr/CF₃OF solutions at 10 K shows anisotropic hyperfine interactions of a single unpaired electron with one nuclear spin of $\text{1}\text{2}$ and (using isotopically enriched ⁸³Kr) two equivalent spins of $\text{9}\text{2}$. The spectrum is attributed to the linear radical KrFKr having a ²Σ_u ground state.     

Reactivity and selectivity in the cyclization of sila-5-hexen-1-yl carbon-centered radicals

A trio of sila-5-hexen-1-yl radicals has been prepared from the corresponding halides by reaction with tri-$\text{n}$-butyltin hydride (deuteride). The radicals possessing a dimethylsilyl function α or β to the carbon radical center demonstrated marked reduction in total (but especially $\text{exo-trig}$) cyclization compared to the all-carbon system. The γ-silyl radical behaved, contrariwise, quite comparably to the all-carbon system. The difference in cyclization found in the α-silyl radical was demonstrated to result from both a pronounced decrease in cyclization rate $\text{via}$ the expected $\text{exo-trig}$ mode and $\text{and from a significantly enhanced rate of hydrogen abstraction from TBTH}$. Both the α- and γ-silyl radicals cyclized $\text{via}$ the $\text{endo-trig}$ mode at rates close to that of the parent 5-hexen-1-yl radical itself. The cyclizations studied were demonstrated to be irreversible. The kinetic control thus shown by the preferred formation of $\text{endo}$ cyclized product from the α- and β-silyl radicals is highly unusual and represents $\text{the first report of carbon-centered 5-hexen-1-yl type radicals violating the Baldwin-Beckwith rule}$$\text{exo-trig}$ cyclization preferred by 5-hexen-1-yl radicals). Rationalization of the cyclization behavior of the α- and γ-silyl radicals involves both steric and electronic factors. The behavior of the most unusual case, the β-silyl radical, which has the lowest cyclization propensity and no $\text{exo}$ mode product, remains largely unexplained because its hydrogen abstraction rate from TBTH is unavailable as yet. Some speculative considerations involving the preferred radical conformation in this system and its relation to cyclization are given.     

Photochemistry of phenyl alkyl ketones adsorbed on zeolite molecular sieves. Observation of pronounced effects on Type I/Type II photochemistry

The photolysis of phenyl alkyl ketones adsorbed on a number of commonly available zeolites (molecular sieves) can result in dramatic changes in Type I/Type II photochemistry.The photochemistry of ketones in ordered environments is a topic of current interest^2–4. Environmental effects can have important influence on the conformational flexibility of organic molecules, which in turn can affect the outcome of photochemical reactions⁵. Two recent reports^2,3 on the Norrish Type II reaction in ordered media prompts us to report our initial studies of the photochemistry of a number of phenyl alkyl ketones adsorbed in zeolites.Zeolites are crystalline aluminosilicates of usually well-defined structure⁶. Within the zeolite framework are a system channels and cavities of varying dimensions(2 – 13Å)⁶, some of which are capable of adsorption of large organic molecules (e.g., substituted benzenes). Thus the possibility that the internal spaces (or void volumes) of zeolites can exert topological control on organic photochemical reactions warrants investigation, since it is well-known that zeolites display shape-selective catalytic and adsorptive properties in important industrial chemical processes¹⁰. However, only a handful of reports of photochemical reactions on zeolites are known^4,7–9; the majority of these concern the catalytic splitting of water⁹. In this study, several commonly available zeolites were studied, and the results are compared to those obtained in homogeneous solution.Phenyl alkyl ketones $\text{1}$ - $\text{3}$ were employed in this study. The photochemistry of valerophenone $\text{1}$, octanophenone $\text{2}$, and α,α-dimethylvalerophenone $\text{3}$ is relatively well-understood in solution^11–13. For $\text{1}$ and $\text{2}$, the photobehaviour is characterized by Type II reaction, to give a triplet 1,4-biradical, which can either fragment, to give acetophenone, or cyclize, to give $\text{cis}$ and $\text{trans}$ cyclobutanols (eqn.1). Type I reaction in not observed. In solution, the ratio of fragmentation of cyclization (F/C) products is ～ 4 for $\text{1}$ and $\text{2}$. In general, the $\text{trans}$ isomer dominates, with t/c = 3 – 5 in benzene, and decreasing to a limit of 1 in more polar solvents (MeOH or micelles)^11-–13. For $\text{3}$. Type I reaction is observed in addition to Type II. The ratio of Type I/Type II product has been reported to be 0.3 in benzene without added thiol, and 0.6 with added thiol¹¹.Ketones $\text{1}$ and $\text{3}$ were deposited on Zeolites Na⁺-A, Na⁺-X, Na⁺-Y, Na⁺-Mordenite and resembling $\text{C}$ is also possible, from which cyclization is prohibited. For $\text{3}$, Type I reaction is known to compete with the Type II process¹¹. Adsorption of this ketone on Silicalite results in reaction via the least-motion pathway, namely Type I reaction, to give benzaldehyde as the aromatic product. Thus the behaviour of this ketone on Silicalite is quite consistent with the explanation offered for $\text{1}$ and $\text{2}$.Na⁺-Y is a large pore zeolite, with a pore diameter of ～8 Å and an internal cavity (supercage) of ～13 Å⁶. Additionally, we have found from related studies¹⁶ that of the zeolites capable of adsorbing benzene-type molecules studied in this work, Na⁺-Y allows the greatest degree of molecular mobility for photogenerated benzyl radical. Thus the observed F/C ratios of less than unity for this zeolite probably reflects the increased mobility of the photogenerated 1,4-biradical, allowing it to undergo ring closure readily. Interestingly, this zeolite also gave an $\text{inverse}$ t/c ratio for cyclobutanols of $\text{2}$.The results for the other zeolites are not readily distinguishable from those observed in solution, although two of these (Na⁺-X and Na⁺-Mordenite) are capable of adsorbing $\text{1}$ - $\text{3}$⁶. In any event, these two zeolites offer a medium for Type I/Type II reaction which essentially duplicate the behaviour in solution without the presence of solvent. Additional studies are in progress to further study the use of zeolites as a medium for photochemical reactions.     

The behaviour of copper and thallium hexafluoromolybdates(V) in acetonitrile

Copper(I), copper(II), and thallium(III) hexafluoromolybdates(V), prepared by the oxidation of the metals in acetonitrile with molybdenum hexafluoride (A. Prescott, D.W.A.Sharp, and J.M. Winfield, $\text{J. Chem. Soc., Dalton Trans.}$, 1975, 963) have been investigated by cyclic voltametry. Half wave potentials, E_{$\text{1}\text{2}$} V vs. Ag^p+/Ag were obtained using a evacuable cell equipped with anexternal Ag^p+/Ag electrode, enabling strict anerobic conditions to be maintained. A number of reversible or quasi-reversible electron transfer processes have been observed, enabling comparison with synthetic work to be made. Results for Cu^I and Cu^II hexafluoromolybdates(V) are in accord with preparative experience. MoF₆. Mo^VI/Mo^VE_{$\text{1}\text{2}$} +1.600V, oxidises Cu metal to Cu^II in MeCN, and Cu^II is reduced by Cu^O to Cu^I , Cu^lI/Cu^IE_{$\text{1}\text{2}$} = +0.750 or +0.710V for Cu^I and Cu^II solutes respectively, Cu^I/Cu^OE$\text{1}\text{2}$ = ?0.720V not reversible. A wave at E_{$\text{1}\text{2}$} = ?0.350V is assigned to Mo^V/Mo^IV by analogy with Ag^I hexafluoromolybdate (D.W.A. Sharp, unpublished work). E_{$\text{1}\text{2}$} data for I₂ in MeCN, I₂/I₃^- = 0.280, I₃^?/I^? = -0.116V, suggest that reduction of MoF₆^? by I is not likely, in contrast to the situation in SO₂ (A.J. Edwards and R.D. Peacock, $\text{Chem. Ind.}$, 1960, 1441). Reduction of MoF₆^? by Cu^o in MeCN should be feasible, but appears to be very slow. Pure Tλ^III hexafluoromolybdate(V) is obtained from Tλ^o and MoF₆ only when the mole ratio MoF₆:Tλ>5:1. Smaller ratios produce yellow solids in which Mo:Tλ is $\text{ca}$. 2:1. Tλ^III is a stronger oxidising agent than Cu^II in MeCN, as oxidation of Cu^I by Tλ^III is rapid and quantitative. However a reversible electron transfer wave assignable to Tλ^III/Tλ^I is not observed in the expected fange +1.600 to +0.710V possibly because of solute-electrode interactions.     

Septorine and N-methoxy septorine,substituted pyrazines from the fungus Septoria nodorum berk

On the basis of ¹H nmr correlations with synthetic analogs, structures $\text{1}$ and $\text{2}$ are proposed for septorine and N-methoxy septorine, two p-hydroxybenzoyl 1-isobutyl substituted pyrazines obtained from the fungus $\text{Septoria nodorum}$ Berk, a parasite of wheat.     

“Spin-charge exchange” in a stableradical-carbanion,and related intermolecular one-electron transfers

An example of a rapid $\text{spin}$-charge exchange in a stable radical-carbanion, with independent radical and anion sites, is described. A related anionization of radicals with HO^? is also reported and interpreted.     

Correlation between the n,π* triplet energy of some acetophenones and the corresponding electroreduction potentials

The half-wave reduction potentials, E_{$\text{1}\text{2}$}'s, of ten acetophenone derivatives have been determined in acetonitrile. A linear free-energy relationship was obtained between E_{$\text{1}\text{2}$} and the n,π^* triplet energy. This correlation enabled an estimate to be made of the n,π^* triplet energy of those acetophenones with π,π^* lowest triplet.     

Laser-induced fluorescence in supersonic nozzle beams predissociation in the Rb2 C1πu and D 1πu states

By exciting Rb₂ in a supersonic nozzle beam with a pulsed dye laser in the C ¹Π_u-X ¹Σ⁺_g and the D ¹Π_u-X ¹Σ⁺_g band system, we find evidence tor different predissociation processes The products appear as follows from the C state, Rb^* (5 ²P_{$\text{3}\text{2}$}) exclusively, and from the D state Rb*(4²D_{$\text{3}\text{2}$}) predominantly, followcd by Rb^*(5 ²P_i-5²S) cascade radiation In addition, a lower bound of D_e(Rb₂X¹Σ⁺_g)? 3939± 10 cm^?1 is obtained.     

Fluorimetric determination of lactate with immobilized lactate dehydrogenase

In measuring inter-phase distribution coefficients (k_{$\text{1}\text{11}$})it is often convenient, and sometimes necessary, to obtain all of the analytical data from one phase. A rigorous formula, applicable to both low and high k_{$\text{1}\text{11}$} values has been derived; measurements of the distribution of mercury, methylmercury and ⁶⁷Cu²⁺ between various pairs of phases with this formula gave k_{$\text{1}\text{11}$} values similar to those obtained from other approaches.     

Temperature dependence of collisional deactivation of Tl(62P32)

The rate coefficients for the collisional deactivation of Tl(6²P_{$\text{3}\text{2}$}) by several gases has been determined at 300°K. This data is compared with that previously obtained at higher temperatures and the Arrhenius parameters calculated. Both the overall rate coefficients and temperature effects display trends similar to those observed for 1(5²P_{$\text{1}\text{2}$}) relaxation. The deactivation of Tl(6²P_{$\text{3}\text{2}$}) by O₂ is shown to proceed by a process involving an equilibrium with Tl(6²P_{$\text{1}\text{2}$}) and electronically excited oxygen, probably O₂(¹Δ_g).     

A highly efficient radical clock as a probe of the mechanism of sulfone halogenation by perhaloalkanes

Halogenation of (endo)-5-(2-i-propylsulfonyl)-2-norbornene 5, a new highly efficient radical probe, shows that if an SET mechanism was occurring in the -α-halogenation of sulfones by perhaloalkanes, it would have to involve a reaction step in which a C-centered radical reacts with CX₄^$\text{.}$ at a rate greater than 10¹⁰ s^?1.     

Energy levels of iodine monochloride near the first dissociation limit

Absorption transitions to vibrational levels close to the A state dissociation limit of ICI have been examined using a two-photon sequential absorption technique. The discrete rotational structures of I³⁷ Cl bands to within 0.7 cm^?1 of the limit have been selectively excited and analysed. A value of 17557.514 ± 0.030 cm^?1 has been obtained for the I(²P^o_{$\text{3}\text{2}$}) + Cl(²P^o_{$\text{3}\text{2}$}) dissociation energy D_e, relative to the minimum of the ICI ground state potential well. The two-photon technique can be used to excite and display separately the high resolution absorption spectra of different isotopic species of a molecule which are contained in a mixture.     

Solvent effects on the nitrogen hyperfine splitting constant of the t-butyl-t-butoxy nitroxyl radical

A decrease in nitrogen hyperfine splitting constant (N-hfsc) with increasing solvent polarity is reported for $\text{t}$-butyl $\text{t}$-butoxy nitroxyl radical produced by trapping $\text{t}$-butoxyl radical with 2-methyl-2-nitrosopropane.