Chapter 13 Spectroscopic Methods of Identification

If a molecule is subjected to enough energy to break bonds, the molecule fragments into smaller pieces. These fragments provide structural information. Exposure to infrared light causes the bonds in a molecule to vibrate, but not break. Spectroscopy techniques analyze how radiation of a particular energy is altered by interaction with a molecule. The mass of the molecular ion is used to give the molecular weight of a sample. When irradiated with infrared light a molecule absorbs energy that will induce molecular vibrations, but this energy is not sufficient to break bonds. A hydrogen nucleus is a charged particle possessed of a property called “spin.” The NMR spectrum for an organic molecule is obtained by first dissolving the sample in a suitable solvent.

Light and Energy

Mass Spectrometry

Radical Cations

The Mass Spectrum

Isotopic Peaks

Determining a Molecular Formula

Absorption of Infrared Light

Stretching and Bending Vibrations

An Infrared Spectrophotometer

Characteristics of an Infrared Spectrum

IR of Common Functional Groups

Rings or 1t-Bonds

His a Magnet

Spin Quantum Number

NMR Spectrometer and the NMR Spectrum

Chemical Shift

lnAuence of Functional Groups on Chemical Shift

Magnetic Anisotropy

n+ 1 Rule

Non-First Order Coupling

Integration

Determine a Structure. Examples 1-3

Determine a Structure. Examples 4-7

Carbon-13 NMR

Two-Dimensional (2D)-NMR

Proteomics