a [1,5] alkyl shift and an electrocyclic ring opening. Proceeding through a [1,5] shift, the walk rearrangement of norcaradienes is expected to proceed suprafacially with a retention of stereochemistry. Experimental observations, however, show that the 1,5-shifts of norcaradienes proceed antarafacially. Theoretical calculations found the [1,5] shift to be a diradical process, but without involving any diradical minima on the potential energy surface. See also 2,3-sigmatropic rearrangement NIH shift Frontier molecular orbital theory References Reaction mechanisms Rearrangement reactions