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Acid-catalysed intramolecular acylation of trans-3-(2-hydroxybenzylidene)-4,5-dihydrofuran-2(3H)-one was studied kinetically in 5–11.5M-HCl, 2–8.8M-HBr, and 5-18M-H2SO4 solutions at 70–105, 70–120, and 80° respectively. The rate dependence on acidity is discussed on the basis of hydration parameter treatments. A kinetic scheme is proposed, visualizing the transition state as leading from the protonated substrate through its cis-form to the products. This scheme is consistent with the hydration parameters and acyl– or alkyl–oxygen fission concerted with acylation, the second being the operative mechanism in halogen acid solutions.

The dipole moments and molar Kerr constants of dimethyl and diethyl malonate in carbon tetrachloride at 25°C are recorded. Details of the equipment and procedures are given. A re-examination of polarity and polarizability of –CO2Me group and the C(sp2)–O bond indicates that the CO2Me group is planar. The CNDO/2 method has been used to deduce the preferred gas-phase conformations of dimethyl malonate. The preferred solution-state conformations of dimethyl and diethyl malonate, indicated by the analysis of experimental and calculated dipole moments and by molar Kerr constants, are shown to be consistent with the theoretical predictions. The experimental data for the investigated dicarboxylic esters may be well interpreted in terms of two rotamer populations centred on two energy minima separated by a barrier of 2–3 kcal mol–1(τ1= 90°; τ2= 90°, and τ1= 90°; τ2= 270°).

The dependence of the kinetics on the wavelenghth of trans-3-(2-hydroxybenzylidene)-4,5-dihydrofuran-2(3H)-one was studied at 220–360 nm in methanol solution for the two consecutive photochemical reactions, geometrical isomerization of the trans- and intramolecular acylation of the cis-substrate. Quantum yields for the first reaction were higher (at 5.20 × 10–5M) than those for the second. The effect of concentration quenching on quantum yields for the latter process was found to be appreciable in the 10–4–10–5M range. This reaction appears to proceed through long-lived T2 states, while isomerization occurs either directly from the singlet excited state S1 or indirectly by crossing of S1 to a triplet excited state T1.

Proton dissociation of XC6H4NCNH6H3YNHEt2(X = H, CO2H, NO2, OMe; Y = H, Me, OEt) has been examined at 293.15 K in aqueous sulphuric acid solutions. Equilibrium constants for the proton dissociation of XC6H4NHNC6H3YNEt2(X = H, CO2H, NO2, OMe; Y = H, Me, OEt) have been measured as a function of temperature, in the range 293–323 K, in 20 wt% aqueous methanol solution. Thermodynamic functions (ΔG°, ΔH°, ΔS°) have been calculated. Experimental data have been discussed and interpreted in terms of linear free energy relationships. Tautomeric equilibrium constants have been evaluated and apparent equilibrium constants separated into the separate contributions of ammonium and azonium forms.