Journal Article 2 nucleus independent chemical shift Clar's aromatic π-sextet 1 Diels-Alder 1 Research Support, Non-U.S. Gov't 1 adaptative natural density partitioning 1 aromatic fluctuation index 1 mehr ... density functional theory 1 electrocyclization 1 harmonic oscillator model of aromaticity 1 para-delocalization index 1 pseudopericyclic 1 transition state 1 weniger ...