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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.

77Se and 125Te chemical shifts have been measured for o-halogenated seleno- and telluro-phenetoles. Correlations exist between these parameters and the halogen electronegativities or the 13C chemical shifts, except for the fluorine derivatives. The chalcogen shifts are related to the shifts of various nuclei in halobenzene derivatives, namely 1H in benzenes, 13C in toluenes, 15N in anilines and 19F in fluorobenzenes. 77Se and 125Te chemical shifts are correlated in the o-halogenated seleno- and telluro-phenetoles and in chalcogen analogues of o-methoxy-selenoanisole and -tellurophenetole: Δδ(Te) = 1.60Δδ(Se). The observed gradient is close to values previously reported for other selenides and tellurides, but differs from the value observed in heterocycles. This observation is discussed.

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.

A linear relationship was observed between the 77Se and 125Te chemical shifts in 14 model heterocycles (including 17 new data). The line slope, 1.3, is discussed in terms of Jameson and Gutowski's expression for the Ramsey paramagnetic term, σP. The shifts are also compared with the 17O chemical shifts in related compounds.

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

o-Carbonyl benzeneselenenyl compounds with COCH3, CHO and COOCH3 as carbonyl functions and SeCl, SeBr, SeSCN, SeSeCN, SeCN and SeCH3 as selenium-containing groups, have been studied by 1H, 13C and 77Se NMR spectroscopy. The IR CO stretching frequencies of these compounds are also reported. If the SeCH3 derivatives are excluded, the compounds mainly adopt a planar ‘cis’ conformation, due to an interaction between the CO group and the selenium atom. The range of over 800 ppm for the observed 77Se chemical shifts makes 77Se NMR spectroscopy a powerful tool for physical organic chemists.

The 77Se chemical shifts of 79 mono- or disubstituted benzo[b]selenophenes are reported. The results in the 2- and 3-substituted derivatives closely parallel those previously obtained in the corresponding selenophenes. The measured parameters also correlate well with those measured in benzo[b]tellurophenes. The 125Te and 77Se chalcogen nuclei appear to be much more sensitive to substituent effects than the more classical nuclei. The effects of Cr(acac)3, Eu(dpm)3 and concentration on the 77Se NMR spectra are briefly discussed.

Selenium-77 magnetic resonance spectra of sulphur-selenium and selenium-selenium isosteres of phenanthrene and some of their 2-substituted derivatives have been recorded and 48 77Se chemical shifts are presented. The two isomers of the studied compounds could be differentiated because the Se nucleus is always more shielded in the ‘trans’ than in the ‘cis’ isomer, the difference varying between 10 and 40 ppm. CNDO calculations have been performed; they allow an electronic model to be proposed which accounts, at least qualitatively, for the NMR results. They also provide an electronic interpretation of the ring opening of the Se-containing ‘cis’ isomers when treated with alkyllithium.

Indirect evidence is provided for (a) the existence of an interaction between the Te d-orbitals and the oxygen lone pair in COR and NO2 substituted compounds and (b) the Δδ(77Se) ≈ 0.6 Δδ(125Te) relationship.