Giovanni Consiglio

Intense shake-up satellites in the XPS spectra of planar and sterically hindered N-piperidyl-nitrobenzenes and -nitrothiophens

Abstract The shake-up satellites present in the O 1s and N 1s energy regions of the XPS spectra of the planar 4-N-piperidyl-nitrobenzene ( 1 ) and 2-N-piperidyl-5-nitrothiophen ( 3 ), and of the sterically hindered 2-N-piperidyl-nitrobenzene ( 2 ), 2-N-piperidyl-3-nitrothiophen ( 4 ) and 3-N-piperidyl-2-nitrothiophen ( 5 ) and, for comparison, of 2-bromo-3-nitrothiophen ( 6 ) have been analyzed with the help of CNDO/S CI calculations. The spectra of the planar derivatives closely resemble these of the related compounds previously analysed, the main satellites deriving from the transition between the highest occupied molecular orbital (HOMO, localized at the donor-ring moiety) towards the lowest unoccupied one (LUMO, localized at the nitro group). Calculations indicate that in the ortho derivatives new relaxation processes are allowed upon N 1s /NO 2 ionization. In 2 , where the angle of rotation θ is closer to 90° than 60°, the NR 2 lone-pair orbital relaxes through space towards the core-ionized N/NO 2 atom. In 4 and 5 , where 45° ⩽ θ ⩽ 60°, both through-ring and through-space relaxations are present. The assignment of the main N 1s /NO 2 line in 1 is discussed.

Mononuclear heterocyclic rearrangements. Part 11. Kinetic study of the rearrangement of (Z)-phenylhydrazones of some 5-alkyl-3-benzoyl-1,2,4-oxadiazoles into 4-acylamino-2,5-diphenyl-1,2,3-triazoles in benzene, dioxane–water, and acetonitrile

The kinetics of the title reactions have been measured at various catalyst concentrations. The 5-alkyl-substituted phenylhydrazones (alkyl = Me, Et, Pri, or But) rearrange more slowly than the 5-H parent compound; moreover the rearrangement rate is little affected by the structure of the 5-alkyl substituent. These facts are considered as evidence against a rearrangement mechanism involving catalyst addition to the C(5)–N(4) bond of the 1,2,4-oxadiazole ring. The observed reactivity pattern can be related to the influence of the 5-substituent on the leaving group ability of the substituent–C(5)–O system.

Kinetics of the reactions of some 5-bromo-2-nitro-3-R-thiophens, 3,4-dibromo-2-nitro-5-R-thiophens, 3-bromo-2-nitro-5-R-thiophens, and 2-bromo-3-nitro-5-R-thiophens with nucleophiles in methanol

The reactivity of some 5-bromo-2-nitro-3-R-thiophens (la–g; R = H, Me, Et, Prn, n-hexyl, Pr1, and But), 3,4-dibromo-2-nitro-5-R-thiophens (IIa and b; R = H and Me), 3-bromo-2-nitro-5-R-thiophens (IIIa and b; R = H and Me), and 2-bromo-3-nitro-5-R-thiophens (IVa and b; R = H and Me) with amines and sodium benzenethiolate has been studied in-methanol at various temperatures. Piperidinodebromination of compounds (la and c) has also been studied in benzene, in dioxan, and in dioxan-water (60 : 40 and 10 : 90). Independent of the position of the alkyl group (meta or para with respect to the leaving bromine), an unexpected alkyl activation has been observed, which represents a further exception to the electron-releasing behaviour of alkyl groups.

Mononuclear heterocyclic rearrangements. Part 14. Rearrangement of some Z-arylhydrazones of 3-benzoyl-5-phenylisoxazole to 2-aryl-4-phenacyl-1,2,3-triazoles in dioxane–water

The kinetics of the title reaction have been measured at various pS+ values. The results show the occurrence of general base catalysis and furnish information about substituent effects on the studied reaction. A reaction mechanism analogous to that proposed for the rearrangement of the arylhydrazones of 3-benzoyl-5-phenyl-1,2,4-oxadiazole is suggested. The reactivity of isoxazole derivatives is much lower than that of 1,2,4-oxadiazole derivatives.

Mononuclear heterocyclic rearrangements. Part 7. Evidence for general base catalysis in the rearrangement of the Z-phenylhydrazone of 3-benzoyl-5-phenyl-1,2,4-oxadiazole into 2,5-diphenyl-4-benzoylamino-1,2,3-triazole in dioxan–water

The title reaction has been studied at various pS+ and buffer concentrations. Kinetic constants for uncatalysed and catalysed pathways have been calculated. A mechanism for the rearrangement is offered.

Amine basicities in benzene and in water

The constants for ion-pair formation with 2,4-dinitrophenol in benzene (KB), and the pKa, values in water, of thirty-three amines have been measured. According to the class of amine, two different situations can be observed: for primary amines and secondary cyclic amines, the effects of structural variations on basicity are higher in water than in benzene; on the other hand, for tertiary amines these effects are similar in the two solvents. KB, Values of primary amines give a good correlation with σ*. The Taft and Hancock equation allows a unifying treatment of KB, values of the various classes of amines.

Kinetics of the reactions of 2-bromo-3,5-dinitrothiophen with ortho-substituted anilines in methanol. An application of the Fujita–Nishioka equation

The rates of anilino-debromination of 2-bromo-3,5-dinitrothiophen (I) by some ortho-substituted anilines (II; X = OMe, Me, Et, Cl, Br, and F) have been measured in methanol. The kinetic results have been treated according to the multiparameter analysis of ortho-effects proposed by Fujita and Nishioka. This treatment of data has also been applied to acid–base equilibria of anilinium ions. The susceptibility constants obtained in the two series of reactions (respectively ρ–2.96 and –2.90, δ 1.31 and 0.56, f–1.83 and –1.70) have been explained by taking into account the structure of the transition states involved.

Mononuclear heterocyclic rearrangements. Effect of the structure of the side chain on the reactivity. Part 3. Rearrangement of some N-(5-phenyl-1,2,4-oxadiazol-3-yl)-N′-arylformamidines into 1-aryl-3-benzoylamino-1,2,4-triazoles in acetonitrile in the presence of triethylamine

The apparent pseudo-first-order rate constants for the title reaction give a curvilinear plot versus tertiary amine concentration, according to the equation kA  (ku, + K1k2[TEA])/(1 + K1[TEA]). This shows the occurrence of two different reaction pathways; the one, independent of [TEA] and the other, dependent on [TEA], which involves a fast conversion of the substrate into an acid-base adduct or an ion pair followed by its slow conversion into the corresponding triazole. The substituent effects on these reactions have also been studied.

Mononuclear heterocyclic rearrangements. Effect of the structure of the side chain on the reactivity. Part 1. Rearrangement of some 3-arylureines of 5-pheny-1,2,4-oxadiazole into 1-aryl-3-benzoylamino-1,2,4-triazolin-5-ones in acetonitrile, benzene, and dioxane–water

The effect of the structure of the side chain both on the mechanism and the reactivity in mononuclear heterocyclic rearrangements has been studied by comparing the base-catalysed rearrangement of some 3-arylureines of 5-phenyl-1,2,4-oxadiazole with that of some arylhydrazones of 3-benzoyl-5-phenyl-1,2,4-oxadiazole. In acetonitrile and in benzene, in the presence of amines, on changing from the side chain CNN (arylhydrazones) to the side chain NCN (arylureines), a strong decrease of the reactivity has been observed (rate ratios ca. 103), but the reaction mechanism is the same for the two series of compounds. In contrast, in dioxane–water, the reactivity variation is much less (rate ratios ca. 25 in the pS+-dependent range) and a change of mechanism is observed. For arylureines and for arylhydrazones, specific- and general-base catalysis respectively has been shown. This is in keeping with the high acidity of arylureines, which in the presence of a strong base can be converted into the corresponding anions and then rearrange to the 1,2,4-triazolin-5-ones.

Mononuclear heterocyclic rearrangements. Part 12. Kinetic study of substituent effects on the rearrangement of the (Z)-phenylhydrazones of some 5-aryl-3-benzoyl-1,2,4-oxidiazoles into 4-aroylamino-2,5-diphenyl-1,2,3-triazoles in dioxane–water at various pS+ values

The kinetics of the title reaction have been studied in the pS+ range 4.0–12.0, at various temperatures. The logarithmic kinetic constants show excellent linear free energy correlations with σ and σn for the pS+- independent and pS+-dependent ranges, respectively. The susceptibility constants obtained (p+0.85 and +1.75, at pS+ 4.50 and 10.00, respectively) show that a larger negative charge is developed in the transition state of the base-catalysed reaction pathway than in that of the uncatalysed, pS+-independent route.