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[摘要]：The phys.-chem. properties of several 1,3-dithiafulvene (DTF) derivs. having a donor and acceptor group in the mol. were studied. The synthesis of these compds. produces selectively the E isomer, but when the compd. is dissolved in CHCl3 isomerization to the Z isomer takes place with a rate that depends on the substituents. The interconversion rate is slow on the NMR time scale; therefore, two sepd. signals are obsd., and they are used to measure the rate const. of isomerization. The equil. const. is, in all cases, very close to 1, and this is coincident with the fact that theor. calcns. of the energy of the two isomers in the gas phase differ by less than 0.1 kcal/mol. The isomerization reaction is completely reversible, and the E isomer can be obtained in pure form by selective crystn. The derivs. with thioalkyl groups have a strong tendency to aggregate in CDCl3. The formation of the aggregates is evidenced from the changes in 1D 1H NMR and DOSY spectra as a function of concn. The compds. are highly delocalized, and this is reflected by the low activation energy for the isomerization. |
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