Ivan P. de Arruda Campos

Synthesis and characterisation of an intermediate in the peroxyoxalate chemiluminescence: 4-chlorophenyl O,O-hydrogen monoperoxyoxalate

The peroxyoxalate system undergoes one of the most efficient chemiluminescence reactions and is the only one supposed to involve an intermolecular chemically induced electron exchange luminescence mechanism, with proven high efficiency. Several reactive intermediates are proposed in the literature, which, upon interaction with an activator dye, lead to excited state generation. In this work, we report the synthesis, spectral characterisation and chemiluminescence properties of 4-chlorophenyl O,O- hydrogen monoperoxyoxalate (1), a compound analogous to one of the proposed reactive intermediates. In the presence of the activator dye 9,10-diphenylanthracene (DPA) alone, 1 does not exhibit any chemiluminescence emission. This fact eliminates compounds of this type as possible reactive intermediates in the peroxyoxalate reaction. However, the addition of various bases [i.e. imidazole, potassium tert-butoxide, potassium p-chlorophenolate and 1,8-bis(dimethylamino)naphthalene] to 1 in the presence of DPA results in high intensity light emission.

Laser-flash photolysis of α-brominated o-xylenes

Abstract The flash photolysis (λ=266 nm ) of four α-brominated o-xylenes in apolar solvents gives two transients characterized, depending on parent compound substitution, as either monoradicals or carbenes, and quinodimethanes. α-Bromomethylbenzyl radical is characterized and the novel species α,α′-dibromo-o-xylylene and o-(α,α-dibromomethyl)benzyl carbene are described for the first time.

Mercury(II) Trichloroacetate. Part II. Formation and Use as a Versatile Reagent in Ferrocene Chemistry

Abstract The preparation of a methanolic solution of mercury(II) trichloroacetate is described. This reagent is used in an improved decamercuration of ferrocene. Decamercurated ferrocene is converted to decahaloferrocenes and used as the starting material in a new method for the synthesis of decadeuteroferrocene. Referee I: T. J. Haas Referee II: P. F. Brandt

Novel stereoselective addition of some nucleophiles to 2,3-bis(methylsulfanyl) norbornenobenzoquinone

Abstract 2,3-Bis(methylsulfanyl)norbornenobenzoquinone undergoes reaction with nitrogen, oxygen, sulfur or carbon nucleophiles to give the trisubstituted adducts containing the new substituent at the ring junction. Their configurations are assigned by 1 H NMR spectroscopy and NOE enhancement experiments.

Olefin photoaddition to 4-oxoisophorone

The intramolecular photocyclization of the enedione moiety to the olefinic moiety in 1, yielding the cage-compound 3, was first described in 1964 by Cookson et al.3 It has been extensively investigated since then, and is part of a proposed 4 solarenergy storage system. This reaction is not a concerted [2+2] cycloaddition and its mechanism ought to be formulated as in Scheme 1, in view of the cumulative results (see ref. 5a and references therein cited) published since 1964.

H-1 and C-13 NMR of some alpha-halo derivatives of o-xylene

Abstract 13C and 1H NMR data for a series of α-halo derivatives of o-xylene are presented. A dynamic 1H NMR investigation of α,α,α′,α′-tetrabromo-o-xylene (5) was performed and the spectrum of the most stable conformer at 213 K is presented. The free energy of activation for the rotation of the CHBr2 groups in 5 are determined for the first time.

Photolysis of a series of α-brominated ortho-xylenes in apolar solvents

The α-brominated ortho-xylenes have been subjected to 254 nm irradiation in deaerated benzene, isooctane and benzene–cyclohexene. The product analysis revealed that homolysis of the C–Br bond is followed by a series of hydrogen abstraction and radical recombination reactions resulting in xylenes more and less brominated than the starting compound. The less brominated products are formed with higher quantum yield when cyclohexene is present, due to hydrogen abstraction by the o-benzyl radical formed initially, together with cyclohexene dimers. Additionally, the formation of 2-bromo-2,4,4-trimethylpentane is observed when isooctane is the solvent. The quantum yields observed for the photolysis of 1 and 2 are higher in benzene than in isooctane, suggesting sensitization by benzene. A biradical intermediate of the type o-quinodimethane was expected in the case of (a) photolysis of the o-benzyl radical formed (biphotonic process) or (b) intramolecular hydrogen abstraction. However, the addition of cyclohexene failed to produce the expected Diels–Alder adduct. The synthesis of the novel α,α-dibromo-o-xylene 3 is reported.

The γ-cis effect in the mercury-199 NMR spectroscopy of substituted vinylmercury halides

The γ-cis effect is identified for the first time in the 199Hg NMR data presented here, being proposed as a new criterion for the distinction between E and Z isomers of substituted vinylmercury compounds.

The importance for cage compound formation of the oxidation potential of the enedionic system in benzoquinone–cyclopentadiene adducts

Some substituted benzoquinone–cyclopentadiene Diels–Alder adducts do not undergo photocyclization to give cage compounds. For the adducts a parallel increase of relative quantum yield and half-peak oxidation potential, measured by cyclic voltammetry, is observed. A large difference between the energy levels of the interacting orbitals is assumed to be responsible for this lack of reactivity.

Differentiation between the like and unlike isomers of dimethyl 3,4-di(p-anisyl)adipate using ¹H NMR spectroscopy

Apresenta-se aqui a diferenciacao entre os isomeros like (igual) e unlike (diferente) do 3,4-di(p-anisil)adipato de dimetila, que foi efetuada pelo uso combinado de espectroscopia de RMN de 1H, simulacao espectral e Mecânica Molecular, correlacionados pelo uso da Equacao de Altona, uma versao generalizada da Equacao de Karplus.