A parity rule for ring currents in π-clamped monocycles†
Abstract
Survival of ring currents in planar monocycles subject to [2 + 2] addition of one, two, three, etc., even-carbon polyene clamping groups is governed by a parity rule. If addition is across positions (i1,i1 + 1), (i2,i2 + 1),…,(ij,ij + 1) for clamps 1, 2,…,j, then, if any of i1,i2,…,ij is odd, current is quenched in the central ring; if all of i1,i2,…,ij are even, the central ring current survives.