Long range electrical field effects in solvolysis and 13C‐NMR shielding of androstanes with halogen, hydroxy and oxo substituents

Abstract

AbstractThe solvolysis of 21 different 3‐ or 17‐androstanyl tosylates or chlorides with halogen, hydroxy or oxo substituents in 17‐ or 3‐position shows rate constant variations in hexafluoro isopropanol of up to 6·3 with regular differences for epimeric substituents. Similar variations ae seen over a distance of ∼10 Å in 13C‐NMR shifts at C‐17‐ones of androstan‐17‐ones with varied halogen substituents in C‐3, whereas the shielding observed at other distant carbon atoms excludes significant through bond effects. It is shown how, on the basis of suitable Coulomb‐type equations and of force field minimized geometries, both the stability variation of carbocationic transition states and the carbonyl group polarization are predictable by linear electric field effects, using the same parametrization.