The primary objective of this experiment is to familiarize with the use of an infrared spectrophotometer. In this experiment, we are to examine the spectra regions of solid and liquid samples.

GCSE Science

Name: Neo Qing Hao

Class: DBT/2B/21

Admission No. : 0208725

Date of Experiment: 20 August 2003

Basic Instrumental Analysis

(CP4009)

Experiment 5:

Infrared Spectroscopy

1. Synopsis

The primary objective of this experiment is to familiarize with the use of an infrared spectrophotometer. In this experiment, we are to examine the spectra regions of solid and liquid samples. Mull technique was used to prepare solid samples and Pellet technique was used to prepare liquid samples. The spectra bands are very important information as it allows chemists to differentiate different functional groups and the concentration of the sample can also be determined from it. By using the correlation chart, we can identify the functional groups. In the prospect of handling infrared spectrophotometer, the most important part will be the sample cells. This is due to the sensitivity of the cells and the specificity of the types of cells.

2. Introduction

Infra-red spectroscopy originate from changes in the vibrational motion of atoms about their mean bond positions associated with the changes in the rotation of the molecule, thus it is also called vibration-rotation spectroscopy.

Infrared spectroscopy is a very useful technique used for the identification of functional groups in organic samples. The absorption peaks are sharper than in ultraviolet or visible regions, and thus easier to identify. Each and every molecule will have a different and unique spectrum, and this is tabulated in the correlation chart.

3. Theory

Basically infrared spectroscopy needs a few chemistry principles to work. It is based on the different types of molecular vibrations in a molecule and dipole moments in the different molecules.

Different molecules have different types of vibrations, basically the different types of vibrations fall into 2 categories of stretching and bending. A stretching vibration involves a continuous change in the interatomic distance along the axis of the bond between 2 atoms.

Stretching vibrations are further divided into 2 categories Symmetrical stretching and Asymmetrical stretching. Symmetrical stretching happens when the 2 atoms go in opposite directions with respect to the third atom they r connected with. While Asymmetrical stretching happens when one of the two atoms moves toward the third atom while the other moves away from the third atom.

Bending vibrations are also divided into in-plane bending and out-of-plane bending. In-plane bending happens when the two atoms remain in the same direction as the third atom, and it is further divided into 2 different phenomena called rocking and scissoring. Rocking happens when the two atoms moved in the same direction, while scissoring happens when the two atoms rock, move towards and away from each other.

Out-of-plane bending happens when the two atoms move out of the same plane as the third atom. It is further divided into two phenomena too, wagging and twisting. Wagging happens when the two atoms ...