A theoretical study of the nitration of eugenol with the nitronium ion

The nitration of eugenol was investigated by using density functional theory (DFT) calculations. Potential energy surface and molecular electrostatic potential of eugenol was constructed in order to find, respectively, the minimum energy conformers and the possible sites for electrophilic attack. Stationary points were located and characterized at the B3LYP/6-311++G(2d,2p) level of theory. A strongly bound π-complex was found, in which the distance between the nitrogen atom of the NO2 moiety and the C1 carbon atom of the aromatic ring is 2.15 Å in the gas phase and 2.06 Å in dichloromethane. The most favorable σ-complex or Wheland intermediate is the result from the interaction between the nitrogen and the C6 ring carbon atom. The transition state that connects both complexes is more resembling the σ-complex. The nitronium ion exothermically reacts with eugenol to give the π-complex without an energy barrier. The next stage of the reaction pathway, π-complex → σ-complex, is endothermic and involves a Gibbs energy of activation of 7.9–8.0 kcal mol–1 (gas phase) and 8.3–8.9 kcal mol–1 (CH2Cl2).

Catabolism of Arylboronic Acids by Arthrobacter nicotinovorans Strain PBA

ABSTRACT Arthrobacter sp. strain PBA metabolized phenylboronic acid to phenol. The oxygen atom in phenol was shown to be derived from the atmosphere using 18O2. 1-Naphthalene-, 2-naphthalene-, 3-cyanophenyl-, 2,5-fluorophenyl-, and 3-thiophene-boronic acids were also transformed to monooxygenated products. The oxygen atom in the product was bonded to the ring carbon atom originally bearing the boronic acid substituent with all the substrates tested.

Electrophilic aromatic substitution in substituted anilines; kinetics of the reaction with 4,6-dinitrobenzofuroxan

Kinetic results are reported for reaction of aniline and six of its N- and ring-substituted derivatives with 4,6-dinitrobenzofuroxan (DNBF) in water - dimethyl sulfoxide mixtures. In acidic solution σ-adducts, the result of electrophilic substitution in the anilines, are formed with bonding between a ring-carbon atom of the anilines and the 7-position of DNBF. Reaction normally occurs at the 4-position of the aniline unless this carries a substituent, when reaction occurs at the 2-position. A value of 2.0 for kH/kD, the kinetic isotope effect, indicates that in the reaction with aniline bond formation is largely rate determining in the substitution pathway. The results allow estimates to be made for the pKa values relating to carbon protonation of the anilines.Key words: electrophilic substitution, σ-adducts, 4,6-dinitrobenzofuroxan, ambident reactivity of anilines.

Prototropic reactions for 1-, 2-, and 4-fluorenamides in the ground and excited singlet states

Absorption and fluorescence spectra of 1-, 2- and 4-fluorenamides (1-FAm, 2-FAm, 4-FAm) were studied in different solvents and at various acid concentrations. This study indicates that the long wavelength absorption band is long-axis polarised in 2-FAm whereas in 1-FAm and 4-FAm, it is composed of long- and short-axis polarised transitions. The —CONH2 group in 1-FAm and 4-FAm is coplanar with the fluorene moiety, whereas the same group in 2-FAm is non-coplanar with the fluorene ring in non-polar solvents, both in S0 and S1 states, but attains coplanarity in the polar and hydrogen bonding solvents in the S1 state. Hammett's acidity scale is not valid for the protonation reaction of amides and a medium effect is observed on the absorption spectra of the monocations in strong sulphuric acid. The prototropic equilibrium for the protonation of ring carbon atom is not established in the S1 state, due to the slower rate of protonation reaction. Proton-induced fluorescence quenching of the monocations is followed before the monocations are being protonated.

N-Picrylethylenediamine – methoxide ion interactions: N-deprotonation and σ-complex formation reactions

The interactions of N-picrylethylenediamine as the HCl salt (PED) with methoxide ion in dimethyl sulfoxide – methanol (DMSO/MeOH) media and with 1,4-diazabicyclooctane in dimethyl sulfoxide have been investigated spectrophotometrically at 25.0 °C. Evidence is presented to show that, in solvent mixtures rich in dimethyl sulfoxide (e.g. 95/5, V/V, DMSO/MeOH), deprotonation reactions at the nitrogen centres on the ethylenediamine occur in preference to reactions in which σ-complexes are formed via addition of CH3O− to one or more ring carbon atoms. The initial 1:1 interaction of CH3O− and PED results in the rapid, reversible deprotonation of the NH centre while the 2:1 interaction is associated with rapid, reversible abstraction of H+ from the NH3+ centre. At mole ratios of CH3O− to PED > 3 a σ-complex is formed as a result of the addition of CH3O− ion to a C-3 ring carbon atom of the di-deprotonated PED. The uv–visible absorption properties of these various species are reported and compared to the properties of corresponding species formed in related systems.