Related Structures. The Electronic Nature of the Acetylene Group'0-, m-, and p- ethynylbenzyl chloride and m-and p-ethynylbeneoic acid have been synthesized and used to determine substituent constants for the ethynyl group (am, 0.205; up, 0.233; am+, 0.330; up+, 0.179). Unlike any other group for which these constants have been determined, the acetylene function exhibits a resonance effect which is reflected in both the u and u+ ...