The reactions of vinyl butyl ether and vinyl butyrate with atomic hydrogen and deuterium lead to addition at the terminal position of the olefins. This observation is consistent with the reactions carried out earlier with other olefins. Both of the absolute rates of addition to vinylbutyl ether and vinyl butyrate, in acetone and hexane, were measured at several temperatures. The relative rates are consistent with only modest stabilization of the transition state of the radical adduct by the alpha-O substituent compared with that of hydrogen atom addition to 1-octene. The relative rates measured in acetone and hexane indicate no significant differential solvation of the ground state relative to the transition structures of the hydrogen atom addition. The kinetics reveal that the early transition states for hydrogen atom addition exhibit little selectivity (vinyl ether versus simple olefin) in either the abstraction of hydrogen alpha to the oxygen or by terminal addition to the olefinic ether and reflects the modest influence of the increased enthalpy of reaction associated with resonance stabilization by the oxygen substituent at the developing radical site.

The gas-phase, carbon-catalyzed,microwave-promoted conversion of methane to ethylene, ethane, acetylene, and hydrogen is reported. A selection of C-1-C-4 hydrocarbons, hexadecane, and a cyclic hydrocarbon, cyclodecane, were also subjected to microwave conversion, resulting primarily in cr-olefins, ethylene, and hydrogen. For methane conversion, the products are reminiscent of those found in methane pyrolysis. Microwave-induced cleavage of the liquid hydrocarbons provides conditions for the stabilization, by rapid thermal quenching in ambient-temperature liquid reagent, of products such as terminal olefins that would be labile under conventional (thermal bath) pyrolysis reaction conditions. The reactions of long chain acyclic and cyclic hydrocarbons involve high temperatures in the region of the spark leading to a cascade of unimolecular scission reactions from initially formed biradicals from cycloalkanes or radical pairs from linear alkanes, largely to the exclusion of intermolecular radical-radical and radical-molecule reactions. The observed products are discussed in terms of the thermochemistry and dynamics of high-temperature unimolecular biradical and radical decomposition reactions, and mechanisms involving reactive surface metal sites. The reaction rates of alkanes were found to increase with the molecular weight of the reactants. Mechanistic pathways consistent with these results are discussed.

The reactions of neat olefins or solutions of olefins in acetone at low temperature with oxygen atoms were examined. O(P-3) atoms were produced by microwave irradiation of He/O-2 mixtures, followed by contact of the plasma with the fluid at low pressure and temperature. Addition of oxygen atoms to olefins results in skeletal rearrangements involving hydrogen and alkyl migration reactions and ring rearrangements of the intermediate oxygen adducts in competition with epoxide formation. While epoxide formation predominates for simple olefins such as 1- and 4-octene with minor yields of rearrangement products, for highly substituted or strained olefins, such as norbornadiene, skeletal rearrangement dominates following oxygen atom addition, When oxidation of norbornadiene is carried out in the presence of a radical inhibitor to suppress secondary oxidation leading to benzene, the novel ring-rearrangement product, bicyclo[3.(2,3)1.0]hex-3-ene-endo-6-carboxaldehyde, is produced from norbornadiene in significant yields.

The solution-phase absolute rate constants (23 degrees C) for the abstraction by atomic hydrogen of 1 degrees, 2 degrees, and 3 degrees allylic hydrogens have been calculated by determining the relative rates of abstraction vs addition, since the absolute rate constants for addition is known. The absolute rate constant for benzylic abstraction by deuterium has also been determined. The rate ratios for 1 degrees, 2 degrees, and 3 degrees allylic abstraction are remarkably similar to those reported for the ratio of rate constants for methyl radical abstraction. The determinations of the rate constants were based on the values for the relative rates of abstraction/addition using atomic deuterium, K-ab(D)/K-add(D), the absolute rate constant for the addition of hydrogen to an olefin, k(add)(H), and the deuterium isotope D D effects for both addition, k(add)(H)/k(add)(D), and abstraction, k(ab)(H)/k(ab)(D).

Recent density functionals and a variety of basis sets were employed in the study of three electronic states of the succinimidyl radical in C-2v symmetry: (2)A(1) (sigma(N)), B-2(1) (pi(N)), and B-2(2) (sigma(0)). The lowest energy sigma(0) state is a genuine (local) minimum, as demonstrated by the harmonic vibrational analysis; the stationary points corresponding to the two remaining states are higher-order saddle points on the potential energy surface. Similar results were obtained with the Moller-Plesset method, while the complete active space calculations predict that the pi(N) state has the lowest total energy. The ring-opening reaction from the sigma(0) state is symmetry allowed and was calculated with the density functional theory to proceed via a true transition state. The beta-scission process was found to exhibit a large secondary deuterium kinetic isotope effect, with k(H)/k(D) = 1.2. The infrared spectra of the open forms of the radical that result from beta-scission reaction were calculated and compared to the calculated spectrum of beta-bromopropanoyl isocyanate.

The low selectivity of benzyl alkyl sulfide fragmentation subsequent to its reaction with atomic hydrogen is indicative of a reaction that proceeds via an early transition state. The competitive reduction of a series of substituted-benzyl alkyl sulfides was insensitive to the substituent on the aromatic ring (rho = -0.13, r = 0.99). The relative rates of fragmentation of a series of the substituted-benzyl alkyl sulfides gave a V-shaped Hammett plot. Both electron-donating and electron-withdrawing groups destabilized the transition state (rho = +0.99, r = 0.999; rho = -0.82, r = 0.992). Since the relative rates of disappearance of the alkyl benzyl sulfides are not substituent dependent, but the relative rates of fragmentation are, a 9-S-3 intermediate is preferred as the structure leading to products.

The hydrolysis of a pyridine solution of lithium tetrakis(N-dihydropyridyl)aluminate (LDPA), which was prepared at 0 °C, yields a mixture of 1,4-, 1,2-, and 2,5-dihydropyridines (DHPs) in a ratio of 26:37:38. The subsequent reversible base-catalyzed condensation of a 1:1 mixture of 1,2- and 2,5-DHPs carried out in the presence of oxygen affords an 89% yield of (±)-anatabine. When the reaction mixture is allowed to stand in the presence of oxygen, anabasine is slowly formed from anatabine by the reaction of the residual DHPs. Anatabine can also be converted into (±)-anabasine by catalytic hydrogenation. Keywords: lithium aluminum hydride, pyridine, anatabine, anabasine.

Four diastereomeric NADH model compounds were synthesized by the reaction of a pinyl substituted Hantzsch ester with dimethylaluminum amide. The reduction of methyl benzoylformate with these models gave both enantiomers of methyl mandelate.

The general methods, photoinitiated or peroxide-initiated free radical chain additions of halomethanes to olefins, yield 1,2-addition products at temperatures ranging from 20 to 100 degrees C. At lower temperatures, -42 to -104 degrees C, a competitive reaction, subsequent to the addition of CCl(2)X(*), yields alkylcyclopropanes. The reactions of 1-octene or 1-hexene and 1-methylcyclohexene with atomic hydrogen carried out in the presence of several transfer agents (CCl(4), CCl(3)Br, CCl(2)Br(2)) initiate a radical chain addition of CCl(2)X(*) and yield cyclized materials resulting from the S(H)i displacement of halogen by a carbon-centered radical. The radical displacement of a halogen on carbon, the reverse of homolytic displacement on cyclopropyl carbon, is dominant at low temperatures. The rate constants for cyclization (k(c)) vs transfer with halomethane (k(t)) showed isokinetic temperatures of -46 degrees C (CCl(4), 1-hexene); -35 degrees C (CCl(4), 1-methylcyclohexene). The isokinetic temperatures for the reactions of the two substrates carried out in the presence of BrCCl(3) were calculated as -204 degrees C (1-octene) and -109 degrees C (1-methylcyclohexene).

The mechanisms for the reaction of allyltributylstannane with a number of fragmentation probes, alpha-substituted acetophenones, were studied. All reactions were shown to proceed through free radical chain sequences since they could be initiated by AIBN and inhibited by m-dinitrobenzene (DNB). alpha-Halo- and alpha-(benzoyloxy)acetophenones (I and II, PhCOCR(1)R(2)X; X = F, Cl, Br, OCOPh; R(1), R(2) = H, Me) yielded the allylation products, PhCOCR(1)R(2)CH(2)CH=CH(2)), through a chain sequence involving as the propagation step: an electron transfer from Bu(3)Sn(*) to I and II, fragmentation of the ketyl anion PhCOCR(1)R(2)X(*)(-), and addition of PhCOCR(1)R(2)(*) to allyltributylstannane. The reactions of alpha-(arylsulfonyl)acetophenones (IIIa-c, PhCOCR(1)R(2)Y, Y = SO(2)Tol-p), however, gave a nearly 1:1 mixture of allyl tosyl sulfone and the corresponding ketone, PhCOCHR(1)R(2). The (1)H and (13)C NMR of the reaction mixture between allyltributylstannane and alpha-(p-methylbenzenesulfonyl)isobutyrophenone substantiated the intermediacy of the tin enolate PhC(OSnBu(3))=CMe(2). These results suggested that a radical addition elimination mechanism was involved in the reactions of IIIa-c with allylstannane. The reaction of alpha-phenylthioacetophenone (IV, PhCOCH(2)SPh) gave both the electron transfer and the addition elimination products (PhCOCH(2)CH(2)CH=CH(2), PhCOCH(3)), indicating that both pathways were involved in the formation of the products.

A mechanism is established for the formation of the products resulting from the solution phase regioselective addition of atomic hydrogen to 1-methylcyclohexene. From this data and new data for the reactions of 1-octene, the absolute rates and activation parameters for the addition of hydrogen atom to an olefin can be extracted. A method was established to determine the absolute rate of addition of a hydrogen atom to a terminal olefin in the solution phase. The addition rate constants, ka (25 °C), to 1-octene [ka = (4.2 ± 3.6) × 109 M-1 s-1] and 1-methylcyclohexene [ka = (4.6 ± 0.8) × 106 M-1 s-1, −78 °C] are found to be in reasonable agreement with the published values for the vapor phase rate of addition to ethylene. The large rate constants are supported by the observation that the activation parameters (Ea = 5.3 ± 2.9 kcal/mol and log A = 14 ± 3.5 M-1 s-1 for 1-octene) are consistent with the values expected for this fast reaction.

Unsymmetric disulfides undergo solution phase reduction with atomic hydrogen regioselectively by displacement at the least hindered sulfur atom. The cleavage of the sulfur-sulfur bond forms mixtures of two thiol and two thiyl radicals. At the temperature at which the reactions are carried out, the thiyl radicals form symmetric disulfides by thiyl-thiyl radical coupling and not by thiyl radical displacement on the starting material. The reaction of atomic hydrogen with an unsymmetric sulfide is a cleavage that favors the formation of the most stable radical. The reaction of phenyl cyclohexyl sulfide produces benzene, cyclohexane, cyclohexyl thiol, and thiophenol. Benzene and cyclohexyl thiol produced from the cleavage of the phenyl-sulfur bond are proposed to arise from the ct-scission of an intermediate formed by ipso-addition of atomic hydrogen to the benzene ring.

The solution-phase reactions of microwave-generated hydrogen atoms with terminal olefins is regioselective. Since addition is to the terminal end of the olefin, the reaction yields a secondary radical which undergoes either reaction with molecular or atomic hydrogen, disproportionation, combination, or addition to another olefin, and in the case of hydrogen atom addition to 1,6-heptadiene, cyclization. The cyclized radicals are formed reversibly, and the final product mixture contains only minor amounts of cis-1,2-dimethylcyclopentane (the product of kinetic control) while the major cyclized product is methylcyclohexane. Although an equilibrium mixture could not be obtained, the dimethylcyclopentyl and 3-methylcyclohexyl radicals were shown to be formed reversibly.

The reduction of a number of mechanistic probes with several borate complexes, NaBH4, Li(C2H5)3-BH, and lithium dimesityl borohydride, has been shown to occur by both an electron transfer-hydrogen atom abstraction mechanism and a hydride transfer process. Although the electron transfer-hydrogen atom abstraction mechanism can nearly always be detected or be initiated, it is usually only a minor reaction, and only when the reducing agent and/or the substrate is sterically hindered or when the acceptor is a strong oxidizing agent is the homolytic pathway preferred.