31519-64-9Relevant articles and documents
PHOTOCHROMIC AND THERMOCHROMIC SALICYLIDENAMINES: ISOMERIZATION IN THE CRYSTAL, INFRARED IDENTITIES AND CONFORMATIONAL INFLUENCE
Carles, Micheline,Eloy, Dominique,Pujol, Louis,Bodot, Hubert
, p. 43 - 58 (1987)
New spectroscopic data on a series of salicylidenamines C6H4(2-OH)-CH=N=R have been collected from crystalline films of nine different derivatives(R=aryl, alkyl).For R=C6H5 and R=C6H4-2-Cl, the photoisomerizations provide coloured species (λmax ca.480 and 540 nm) which subsequently evolve through thermal processes kinetically analysed as the consecutive reactions, X->Y->Z.The second reaction is faster than the first, but it may be observed, owing to the initial presence of Y which is a product of the photoisomerization.These species are respectively identified with the trans (s-E) quinoid structure (X), its cis (s-Z) isomer (Y) and the major cis phenolic tautomer (Z) (cis and trans referring to rotation around the C6H4(2-OH)-CH bond).The X->Y activation energy (ca. 23 kcal mol-1) is in qualitative agreement with the estimated intermolecular interactions occuring for the X->Y transition state which have been simulated from the crystallographic data of the R=C6H4-2-Cl derivative.From the FT-IR spectra of the nine derivatives, some of their deuterated isotopomers (OD) and a second crystalline form for R=C6H2-2-Cl, a series of group frequencies are well identified and assigned.Some specific IR absorption bands belonging to X and Y species are also observed; the Y bands are present as very minor components in the spectra before irradiation.For Z species, the frequencies and the band shapes of the γ(OH) out-of-plane vibrations, and the temperature effects, provide information on the influence of the R group conformation.Through conjugative (R=aryl) and hyperconjugative (R=-CH(CH3)2) effects, the R group modifies the availability of the nitrogen unshared electron pair which strongly influences the γ(OH) frequency.
A study of the tautomers of N-salicylidene-p-X-aniline compounds in methanol
Vargas,Amigo
, p. 1124 - 1129 (2007/10/03)
We have studied the enol-imine→keto-amine tautomeric equilibrium of N-salicylidene-p-X-aniline compounds with X = Me, OMe, NMe2 as electron donor substituents and X = COMe, CN and NO2 as electron acceptor substituents. The equilibrium constants (Ktauo) and standard thermodynamic properties ΔGtauo, ΔHtauo and ΔStauo were measured and calculated in methanol solution at various temperatures, by means of excitation fluorescence spectroscopy. We have analyzed the p-phenylaniline substitution effect on Ktauo and the thermodynamic properties through the Hammett parameters σ. We have performed molecular orbital calculations at the semiempirical AM1 and ab initio HF/3-21G levels to interpret the experimental results, explicitly including the solute-solvent interaction through the formation of an intermolecular hydrogen bond between the salicylidene and methanol molecules. These computational results show a good correlation with the experimental values. An interpretation of the experimental values of TΔSo, based on changes in the molecular structure produced in the enol-imine→keto-amine tautomeric reaction, is proposed.
