Étude théorique (AM1) de l'affinité protonique des polyéthers cycliques (éthers couronnes) et non cycliques (glymes)

Abstract

Semi-empirical calculations at the AM1 level have been used to study the proton affinity (PA) of polyether compounds (dioxane, glymes, and crown ethers). The calculated values, although systematically lower than the experimental ones, are linearly correlated with eight experimental PA's (r = 0.993). Taking into account the considerable conformational changes that take place upon protonation, the result is highly satisfactory and provides an estimate of proton affinity for 9-ether-crown-3 (206.5 kcal mol−1) and glyme-5 (231.1 kcal mol−1). Moreover, this work provides a rationale for the fact that, for the same number of oxygen atoms, glymes are more basic than crown ethers. For the crown ethers, the proton affinity depends on angular strain in the base and on intramolecular hydrogen bonds in the cation. Key words: protonation, reactivity, glymes, crown ethers, coordination.