“…More details of our theoretical approach are given in the Supporting Information; the complete theoretical background will be explained elsewhere. [10] With this model, we calculate tunneling levels with energies À2D,ÀD,D,2D for stem rotation quantum numbers k stem = 0, AE 1, AE 2,3, respectively, as in the 1D models for hindered stem rotation only. [1,9] The splittings D,2D,D between consecutive levels in these quartets show the measured 1:2:1 ratio, typical for sixfold hindered rotation tunneling in the high-barrier limit.…”