Infrared spectroscopy.

https://www.youtube.com/watch?v=EP0RiWQhkXQ

Key idea about organic compounds

The bonds are constantly vibrating, two main types of vibration are bending and stretching

Stronger bonds vibrate faster than weaker

if bond is between two heavy atoms then the vibration will be slower

These bonds can absorb radiation which has same frequency as bond vibration

Where does the radiation absorbed by bonds lie

In the infrared region of electromagnetic spectrum.

What happens when bond absorbs radiation

The degree of stretching and bending increases, so if we pass our infrared radiation through a sample of our organic molecule, then the bonds will absorb specific frequencies

An absorption frequency can be shown with this

What does the % transmittance tell us

How much infrared radiation passes through the sample.

What does peak show us

Shows us that infrared radiation has been absorbed

What does x axis show

Wave number, it is the number of wavelengths per centimetre,

Whats fingerprint region

Below 1500cm-1, we have a fingerprint region, this is a complex series of peaks, which are specific to the molecule being studied

Because of complexity, this region analysed by computer

What is the common peak of organic compounds

Around 3000 cm-1, this is caused by vibration of C-H bonds.

What is the peak of O-H groups in alcohol

A peak of 3200-3600 cm-1

What is peak of C-O bond in Oh group

1000-1300 cm-1

What is peak of C=O double bond in carbonyl group in aldehydes / ketones.

1630- 1820 cm-1, mainly centres near 1700

What is the peak of O-H bonds in carboxylic acids (they also contain C=O double bond in carbonyl group)

Broad absorption peak 2500-3300 cm-1

Combination shows presence of carboxylic acid.

C-O nond can also produce peak of 1000 and 1300 cm-1

Practical applications of IR

Monitors air pollution from car exhausts (e.g carbon monoxide / nitrogen oxide)

Can also be used in breathalysers to check level of alcohol in breath