Infrared spectroscopy Flashcards
What is IR?
A modern analytical technique used to determine the functional group in an organic compound
Carbonyl group peak
A Sharp narrow peak at 1700cm-1
OH group in alcohol peak
A fairly broad peak at around 3000cm-1
OH group in acid peak
A very broad peak around 3000cm-1
What happens when a molecule absorbs infrared radiation?
Makes the covalent bond vibrate more in a stretching or bending motion
What affects the mount of vibration of a covalent bond when a beam of infrared radiation is passed through it?
Bond strength
Bond length
Mass of each atom in the bond
How does IR spectroscopy work?
Each bond has a unique vibrational frequency in the infrared region of the electromagnetic spectrum
Covalent bonds absorb radiation of same frequency as their vibrational frequency when a beam of infrared radiation is fired at sample
Infrared radiation emitted will be missing frequencies that have been absorbed: identify functional group
What do peaks on an infrared spectroscopy graph represent?
The absórbanme of energy from the infrared radiation
Identifying a carboxylic acid
Very broad thumb peak = carboxylic acid O-H group
Sharp fingerprint peak = C=O group
Fingerprint region
Area of infrared spectrum below wave number 1500cm-1
What does fingerprint region represent?
Many peaks caused by complex vibrations of the whole molecule
It is unique to every compound = used to identify it
How can fingerprint region be used to identify a compound?
Match to a database on the computer
