The bicyclo[2.1.1]hexan-5-yl and the 5-deuteriobicyclo[2.1.1]hexan-5-yl radicals have been examined using ESR. A comparison of the spectra confirmed that geometry around C5 is pyramidal and showed highly stereoselective long-range spin-transfer from C5 to the endo proton on C6; a(H6endo)=28.22 and a(H6exo)=0.49 G. A potential curve for the out-of-plane bending motion of the C5–H5 bond, selected from