1 Define the following a Infrared spectroscopy b Stretching

1. Define the following: a) Infrared spectroscopy b) Stretching vibration c) Bending vibration

Solution

A-Infrared spectroscopy involves the interaction of infrared radiation with matter. It covers a range of techniques, mostly based on absorption spectroscopy and it is a characterization tool chemists use to help determine the molecular structure.IR working principle is that functional groups absorb specific frequencies of energy based on their structure. When a functional group absorbs energy, it can vibrate in a bending or stretching mode and the characteristic energy for this vibrational mode is reported in wavenumbers. In general, stronger bonds vibrate at higher wavenumbers, as do bonds between atoms varies in size. IR is a reliable and sensitive technique.
wavenumber = 1 / wavelength (centimeters)
For a molecule to absorb IR, the vibrations or rotations within a molecule must cause a net change in the dipole moment of the molecule. The alternating electrical field of the radiation interacts with fluctuations in the dipole moment of the molecule. If the frequency of the radiation matches the vibrational frequency of the molecule then radiation will be absorbed, causing a change in the amplitude of molecular vibration.

B-STRETCHING VIBRATIONS- It means the change in the inter-atomic distance along the bond axis.Stretching vibrations change bond lengths.There are two types of stretching vibrations.In symmetric stretching, two or more bonds vibrate in and out together. In asymmetric stretching, some bonds are getting shorter at the same time as others are getting longer.

C-BENDING VIBRATIONS-Bending vibrations change the angle between two bonds. There are four types of bending vibration.

1-Scissoring is the movement of two atoms toward and away from each other.

2-Rocking is like the motion of a pendulum on a clock, but an atom is a pendulum and there are two instead of one.

3-Wagging is like the motion in which a person makes a \"V\" sign with his fingers and bend them back and forth from the wrist.

4-Twisting is a motion as if the atoms were walking on a treadmill.