The rate constants, k,, for the abstraction of a hydrogen atom from a wide variety of organic substrates at 30" have been correlated with the strengths of the C-H bond that are broken, D[R-HI (in units of kcal/mol). Two empirical relations have been derived, one for tertiary peroxy radicals,and one for secondary peroxy radicals,These equations hold extremely well for hydrocarbons and reasonably well for substrates containing heteroatoms. The activation energies and pre-exponential factors for the oxidation of some hydrocarbons by I-butylperoxy radicals have been measured and the empirical relation derived. If D[I-ROO-H] is taken as 88 kcal/mol, this yields the Polanyi equation,where AH is the heat of the hydrogen abstraction reaction. These empirical equations permit the calculation of the rate constants for chain propagation in the autoxidation of many organic substrates at 30' and also at other temperatures.

Ground-state Al atoms react with symmetric cyclic and acyclic ethers at 77 K in a rotating cryostat to give a host of mononuclear organoaluminium compounds. Magnetic parameters determined from EPR spectra given by Al atoms and acyclic ethers are consistent with the formation of novel C-C and C-H aluminium atom insertion products. A third species has been tentatively assigned to the product given by Al atom insertion into the C-0 bond. In addition a carboncentred radical is formed by loss of a hydrogen atom from carbon adjacent to the alkoxyl group. In contrast the cyclic ethers are resistant to alumino hydride formation and in most cases a carbon radical resulting from ring opening at the C-0 bond is formed. Mono-and di-ligand complexes, AICether] and AICether], , are tentatively identified and may be the primary intermediates for all the reactions that occur.7 Issued as NRCC no. 31481.

Preexponential factors and activation energies are reported for the transfer of a hydrogen atom from phenol, β-naphthol, aniline, β-naphthylamine, thiophenol, and β-naphthalenethiol to a tertiary alkylperoxy radical ((CH3)3COO• and C2H5C(CH3)2OO•). The A-factors fall in the range 2 × 104 to 2 × 107 M−1 s−1 and increase in the order C6H5SH ~ β-C10H7SH ~ β-C10H7NH2 < C6H5NH2 ~ β-C10H7OH < C6H5OH while the activation energies fall in the range 1 to 5 kcal mol−1 and increase in the order C6H5SH ~ β-C10H7SH < β-C10H7NH2 ~ β-C10H7OH < C6H5OH ~ C6H5NH2. Differences in activation energies and preexponential factors are not consistent with a reaction mechanism which attributes low activation parameters solely to an equilibrium between the reactants and a hydrogen bonded free radical – reactant complex, followed by H-atom transfer within the complex.

No abstract

Reaction of 63Cu atoms with CO has been studied in inert hydrocarbon matrices in a rotating cryostat at 77 K by EPR, FTIR, and UV/visible spectroscopy. CuCO and Cu(CO)3 have been identified by EPR spectroscopy. CuCO has the magnetic parameters 63 = 3961 MHz, an = 191 MHz, and g = 1.9966 and is a linear molecule with most of the unpaired spin located in an sp-hybridized orbital on Cu. It is unstable and disappears rapidly above 77 K. Cu(CO)3 is a planar trigonal radical with a 2A2" electronic ground state and a17 = 11.2 MHz which indicates significant unpaired spin population on the ligands. It has three infrared bands at 1998,1988, and 1978 cm"1 which are assigned to the CO stretching mode of a Dlh molecule in three different trapping sites and is significantly more stable than CuCO. There are no bands in the FTIR spectra from Cu(CO)2. Cu2(CO)6 is formed in significant yields in adamantane and cyclohexane at 77 K and has a major CO stretching mode at 2035 cm"1. Optical spectra of Cu(CO)3 and Cu2(CO)6 in adamantane have 2A/ «-2A2" and * *a electronic transitions at 565 and 405 nm, respectively. 0.25.We have recently performed a more thorough spectroscopic (1) Issued as NRCC No. 29518.