Experimental and Theoretical Evidence for Aromatic Stabilization Energy in Large Macrocycles

Enhanced thermodynamic stability is a fundamental characteristic of aromatic molecules, yet most previous studies stabilization energy (ASE) have been limited to small rings with up 18 ?-electrons. Here we demonstrate that ASE can be detected experimentally in ?-conjugated porphyrin nanorings Hückel circuits 76–108 This conclusion supported by analyzing redox potentials calculate the change for isodesmic reactions convert an ring antiaromatic or vice versa. It also barriers conformational equilibria disrupt aromaticity transition state. Both types experiment indicate cationic display ASEs 1–5 kJ mol–1. Density functional theory calculations reproduce results both and predict range 1–16 The experimental are compared [18]annulene ?11 mol–1, deduced from analysis [16], [18], [20]annulene. Calculated energies give ?37 mol–1 [18]annulene. work contributes understanding large macrocycles.