Studies of Sterically Challenging Polycyclic Aromatic Systems

Abstract

For students of elementary organic chemistry, the class of molecules known as "polycyclic aromatics" conjures up images of fused ring systems that must be flat. After all, one of the supposed prerequisites for aromaticity is a strict alignment of p-orbitals, which define an area of space through which electrons may orbit around parent and adjacent atoms. However, aromatic molecular conformations are not so strictly limited as introductory lessons might suggest. Large acenes are sensitive to both intramolecular and intermolecular forces, making non-flat conformations, such as bowls, ribbons, and waves more common than not. The concomitant opportunities to predict, computationally, and to determine, experimentally, how the addition of a substituent at one position or replacement of one moiety by another affects the lowest energy conformation are what make this vein of synthetic organic chemistry research so exciting.

This work details three projects aimed to better understand crowded polycyclic aromatic architectures: (i) the investigation of a three-step synthesis of tetradecaphenylpentacene; (ii) the introduction of very bulky groups (i.e., tert-butyl and carboranyl) into acenes by using crowded cyclopentadienones; and (iii) the development of a method for the synthesis of a class of acenes derived from pyrene.