Derek C. Nonhebel

SPECTROSCOPIC STUDIES OF TAUTOMERIC SYSTEMS. III. 2-ARYLHYDRAZONES OF 1,2,3-TRIKETONES

Abstract The IR and NMR spectra of a range of 2-arylhydrazones of 1,2,3-tricarbonyl compounds have been recorded. Compounds containing different end groups in the 1,2,3-tricarbonyl system can exist in two different tautomeric forms. The influence of electronic and steric factors on the structure of the preferred tautomer is discussed.

Reactions of cupric halides with organic compounds—III : 9-Alkyl and 9-arylanthracenes

Abstract 9-Alkyl and 9-arylanthracenes have been shown to undergo halogenation with cupric halides to give good yields of their 10-halogenated derivatives. Electron-donating groups in 9-arylanthracenes were shown to increase the rate of reaction. The results are interpreted in terms of a ligand-transfer mechanism.

The influence of α-trialkylsilyloxy groups on the rate of ring opening of cyclopropylmethyl radicals

Abstract The rate of ring opening of α-trialkylsilyloxycyclopropylmethyl radicals is about ten times slower than of the cyclopropylmethyl radical at 298K.

The role of stereoelectronic factors in the oxidation of phenols

Abstract The oxidative coupling of both 3,5-dimethylphenol and phenol leads to the ortho-ortho and ortho-para coupled products as the predominant C-C dimers: stereoelectronic factors determine the preferred mode of approach of the phenoxyl radicals.

On the mechanism of hydrogen transfer by nicotinamide coenzymes and some dehydrogenases

Abstract The course of the oxidation of 2 ,2-dimethylcyclopropylmethanol and 2 ,2 ,3,3-tetramethylcyclopropylmethanol by horse liver alcohol dehydrogenase and NAD + has been investigated. In neither case were ring opened products detected which, in agreement with previous observations, provides no evidence for the intermediacy of radicals in these reactions. The stability of several substituted cyclopropylalkyl radicals has been investigated by e.s.r. spectroscopy and the results are discussed with respect to cyclopropane-containing probes of the mechanism of oxidation of lactate dehydrogenase.

Reactions of copper(II) halides with aromatic compounds—IX: Reactions of 1- and 2-alkoxynaphthalenes

Abstract 2-Alkoxynaphthalenes undergo halogenation with copper(II) halides in the 1-position though 2-benzyloxynaphthalene with copper(II) bromide gives additionally di-β-naphthol, 1-benzyl-2-naphthol, and benzyl bromide. The reaction of 1-alkoxynaphthalenes with copper(II) halides leads to 1-alkoxy-4-halogenonaphthalenes and 4,4′-dialkoxy-1,1′-binaphthyls. 8-Chloro-1-methoxynaphthalene is afurther product from the reaction of 1-methoxynaphthalene and copper(II) chloride. The reactions are postulated to proceed via the radical cation of the alkoxynaphthalene formed in an electron-transfer reaction. This can then either react further with the copper(II) halide or dimerize.

Oxidative coupling of phenols. Part 10. The role of steric effects in the formation of C–O coupled products

The formation of C–O coupled products in the oxidative coupling of phenols is hindered by bulky ortho-substituents in the aryloxyl radical intermediates as shown by the predominant formation of the ortho-ortho-C–C coupling products in the oxidation of o-t-butyl- and 2,4-di-t-butyl-phenol. 3,5-Di-t-butyl-phenol gives exclusively the ortho-O-dimeric product as steric effects prevent the sandwich approach of two aryloxyl radicals necessary for C–C coupling.

Reaction of cupric halides with organic compounds—II : 9-Halogenoanthracenes

Abstract 9-Bromoanthracene and 9-chloroanthracene with cupric chloride and cupric bromide respectively give only 9-bromo-10-chloroanthracene. The reaction is postulated to proceed by a radical mechanism. Reactions of 9-halogenoanthracene with other halogenating agents were also examined.Abstract 9-Bromoanthracene and 9-chloroanthracene with cupric chloride and cupric bromide respectively give only 9-bromo-10-chloroanthracene. The reaction is postulated to proceed by a radical mechanism. Reactions of 9-halogenoanthracene with other halogenating agents were also examined.

Reactions of cupric halides with organic compounds—V: Reactions of 9,10-dialkyl- and 9-alkyl-10-arylanthracenes

Abstract 9-Aryl-10-methylanthracenes undergo reaction with cupric halides to give the corresponding 9-aryl-10-halogenomethylanthracenes. 9-Ethyl- and 9-benzyl-10-methylanthracenes similarly undergo reaction at the Me group rather than at the Et or Bz groups to form the halogenomethyl compound. These results indicate that the 9-alkyl-10-anthrylmethyl radical is more stable than the radicals which would be formed by hydrogen abstraction from the Et or Bz groups. These reactions also gave products in which alkyl groups were replaced by halogen. A mechanistic interpretation of these results is advanced. The reactions of 9-alkyl (or aryl) 10-methylanthracenes with N-bromosuccinimide were also examined.

Ring opening of oxiranylmethyl and 3-methyl-3-oxetanylmethyl radicals

Abstract Oxiranylmethyl and 3-methyl-3-oxetanylmethyl radicals were generated from the corresponding bromides and their rearrangements to allyloxyl and 2-methylprop-2-enyloxymethyl radicals respectively, were studied by kinetic EPR spectroscopy. The former radical was shown to ring open with a rate constant o⪢ 4 x 108 s−1 at 25°C. The following kinetic parameters were measured for ring opening of the latter radical: k(25°C) = 8.9 x 102 s−1, log[A/s−1] = 13.97, E/kJ mol−1 = 63.3. Comparison of this data with that of related radicals supported the proposal that the transition state for β-scission of three-membered and four-membered cycloalkylmethyl radicals has dipolar character.