E-Z isomerization and aggregation phenomena of dithiafulvenes in CHCl3.
The physical-chemical properties of several 1,3-dithiafulvene (DTF) derivatives having a donor and acceptor group in the molecule were studied. The synthesis of these compounds produces selectively the E isomer, but when the compound is dissolved in CHCl(3) 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 separated signals are observed, and they are used to measure the rate constant of isomerization. The equilibrium constant is, in all cases, very close to 1, and this is coincident with the fact that theoretical calculations 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 crystallization. The derivatives with thioalkyl groups have a strong tendency to aggregate in CDCl(3). The formation of the aggregates is evidenced from the changes in 1D (1)H NMR and DOSY spectra as a function of concentration. The compounds are highly delocalized, and this is reflected by the low activation energy for the isomerization.
Fracaroli
Alejandro M
AM
Instituto de Investigaciones en Físico Química de Córdoba, Departamento de Química Orgánica, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Ciudad Universitaria, X5000HUA Córdoba, Argentina.
Granados
Alejandro M
AM
de Rossi
Rita H
RH
D002627:Chemistry, Physical; D002725:Chloroform / Q000737:chemistry*; D006573:Heterocyclic Compounds, 1-Ring / Q000737:chemistry*; D008958:Models, Molecular; D015394:Molecular Structure; D013237:Stereoisomerism
C551685:1,3-dithiafulvene; D006573:Heterocyclic Compounds, 1-Ring; D002725:Chloroform