Functionalization of Semiconductor Surfaces

CHAPTER 4

Pericyclic Reactions of Organic Molecules at Semiconductor Surfaces¹

KEITH T. WONG AND STACEY F. BENT

4.1 INTRODUCTION

Pericyclic reactions comprise an important class of the chemistry of unsaturated organic molecules. Woodward and Hoffmann first proposed the concept of pericyclic reactions in 1965 [1]. These are reactions that are thought to occur via a concerted process involving a cyclic transition state, without the formation of intermediates. As a result of their concerted nature, pericyclic reactions are known to provide high stereoselectivity [2]. This chapter focuses on a particular type of pericyclic reaction, cycloaddition reactions, in which π electrons from two or more unsaturated reactant molecules form new σ bonds between reactants to create a cyclic product. Due to the aforementioned stereoselectivity and their ability to form new carbon–carbon bonds and new carbon rings, cycloadditions play a central role in organic synthesis [3,4]. The two types of cycloaddition reactions considered in this chapter are the [2+2] cycloaddition and [4+2] cycloaddition, where the reaction is named for the number of π electrons of each reactant molecule. [4+2] cycloaddition is also known as the Diels–Alder reaction.

The Woodward–Hoffmann selection rules describe the reactivity of such cycloadditions. Symmetry analysis of the parity of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO), as depicted in Fig. 4.1, indicates that the [2+2] ...