Analytical chemistry 2

Mass spec cont.IR absorption spec

Mass spec starter

1. What are the 4 main stages of mass spec?1. Ionisation2. Acceleration3. Deflection4. Detection

Mass spec for ethanol - interpret

1. M+2. Base peak

3.4. 5.

Infrared Spectroscopy•Visible light is made up of a continuous range of different electromagnetic frequencies.....so is Infrared radiation (the eye just can’t see it)•Each frequency of light (including infra-red) has a certain energy.

How IR spectroscopy works…

•Shine a range of IR frequencies, one at a time through a sample of organic compound and at some of the frequencies the energy will be absorbed. •A detector on the other side of the sample would show that some frequencies are absorbed whilst others are not.

• If a particular frequency is being absorbed as it passes through the compound being investigated, it must mean that its energy is being transferred to the compound.

• Energies in infra-red radiation correspond to the energies involved in bond vibrations.

Bend and Stretch

• In covalent bonds, atoms aren't joined by rigid links;

• the two atoms are held together because both nuclei are attracted to the same pair of electrons.

• The two nuclei can vibrate backwards and forwards - towards and away from each other - around an average position.

All molecules absorb infrared radiation; absorbing energy makes the bonds vibrate.

Every bond vibrates at its own frequency, dependant upon bond strength, bond length and the mass of atoms involved in bond.

STRETCHING

BENDING

Fingerprint regions

• You must be able to identify the following peaks.– C-H in alkanes/alkenes/aldehydes– O-H in alcohols/carboxylic acids– N-H in amines– C=O in aldehydes and ketones– C-X in halogenoalkanes

Which functional groups are present in this spectrum?

Which functional groups are present in this spectrum?

Which functional groups are present in this spectrum?