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A general procedure for Te-alkylated tellurolesters synthesis is reported. The carbonyl i.r. frequencies and 13 C chemical shifts of these compounds are compared to the O, S and Se analogs. The origin of the electronic interaction between the carbonyl group and the heteroatom is shown to depend on this latter nature: whereas a combination of both inductive and mesomeric effects is to be taken into account for O. This effect is mainly inductive for Se and Te. In the case of S-compounds, no such a simple model can be involved. The reason of which might be the participation of the 3d-orbitals to the electronic system. Moreover, the previously reported Te heavy atom effect has been detected on the α methylene groups exclusively.

When treated with alkylithium, the two cis and trans isomers of the title compounds react quite differently: while the trans compounds undergo a classical metallation, in the cis ones, a ring opening occurs in the selenophenic moiety. The u.v. spectra of the two isomers are also clearly distinguished. Selenium 77 magnetic resonance, enhanced by CNDO calculations, has also shown different behaviours, opposite to proton and 13 C magnetic resonances. In fact, proton magnetic resonance measurements have evidenced a great analogy between the title compounds and both the thiophen and benzo(b) thiophen series.

A study by 13 C NMR of some esters and their chalcogen analogs is presented: R 1 C(O)XR 2 , (X  O, S, Se, Te), (R 1 , R 2  alk, ar). The chemical shifts are discussed in the scope of the mutual interaction between R 1 and R 2 through the carbonyl group and through the heteroatom. The results are in agreement with a recent study by 77 Se NMR of the selenolesters: they confirm the importance of the resonance form in these type of compounds.

In order to synthesize new tellurium heterocycles, we prepared o -halogenotellurobenzoyl chlorides. We present and discuss here the results of a 13 C NMR study of these compounds, together with other intermediates that we have isolated during our synthesis and two new tellurium heterocycles.

13 C NMR spectra of the title compounds have been fully assigned. The results have been compared with those relative to other chalcogenated compounds, such as anisole, phenyl benzoate, benzofuran,… and their analogs. In chalcogenochromones and -coumarines, the heteroatom lone pair delocalization spreads to some extent over the heterocyclic part of the molecules, while in chalcogenochromanones and -indoxyles, it only extends to the homocycle. This electronic effect seems also to affect the heavy atom effect exhibited by Te-containing compounds.

Resume Les spectres infrarouges (4000-200 cm −1 ; vapeur solide et solution dans des solvants neutres et accepteurs de protons) et Raman (4000-100 cm −1 solide et solution) des benzoselenophene et benzotellurophene ont ete enregistres. Une attribution complete des vibrations fondamentales est proposee. L'evolution des nombres d'onde des vibrations fondamentales pour une serie de benzoheterocycles monoheteroatomique C 8 H 6 X avev X = O, S, Se et Te est analysee.

Resume We have studied by i.r. spectroscopy the position of the carbonyl band of various tellurolesters. We have seen a splitting of the v C0 band, attributed to a Fermi resonance. This assignment is supported by solvent and temperature effects.

We report the selenium 77 chemical shifts in twenty selenolesters R 1 -C(O)-Se-R 2 . The δ( 77 SE) variations with the nature of R 1 and R 2 are discussed within the scope of the resonance interactions between selenium and carbonyl. The most important form in the selenolesters studied seems to be