Computed Spectral Properties and Structure Identification

This chapter focuses on the use of quantum chemical computations to help identify chemical structure. It inspires the routine use of computed spectra to aid in structural identification. The chapter begins with a discussion on computed bond lengths and angles. Next, it talks about IR spectroscopy. A common use of computed vibrational frequencies is to ascertain the identity of an unknown structure by comparison with experimental IR spectra. Nuclear magnetic resonance (NMR) spectroscopy probes the energy required to flip a nuclear spin in the presence of a magnetic field. The chapter describes a number of approaches toward computing chemical shifts and coupling constants, particularly probing for adequate treatments of the quantum mechanics (QM) and basis sets. It examines some procedures for using computed NMR spectra to assist in identifying chemical structure. Finally, the chapter presents a few case studies where computation played an important role in determining the chemical structure.