Synthesis and nuclear magnetic resonance spectroscopic properties of some acetylenic tellura fatty acid esters

Abstract

Five positional isomers of acetylenic tellura stearate ( 1– 5) have been synthesized by three different routes. The number of methylene groups located between the acetylenic system and the tellurium metal varies from 0 to 4. The 1H and 13C NMR spectroscopic properties have been studied. The tellurium atom induces strong deshielding effects on the adjacent methylene protons, which in combination with the deshielding effects of the acetylenic system allows most of the methylene groups between the tellurium and the triple bond to be identified by 1H NMR spectroscopic analysis. The tellurium causes a very strong shielding effect (ca. −27.1 ppm) on the carbon shift of the adjacent α-methylene carbon atom, but weak deshielding effects on the β-(ca. +2.6 ppm) and γ-(ca. +2.3 ppm) methylene carbon atoms. Carbon shifts of methylene carbon atoms, especially those which are located between the tellurium atom and the triple bond, are found very much upfield ( δ C 0.65–4.81) and in one case in the negative region ( δ C−17.95) of the 13C NMR spectrum. Most of the signals of the carbon nuclei of these analogue have been identified and from the results of these analyses the number of methylene groups between the acetylenic system and the tellurium atom can be determined.