Analytical Techniques

Question 1

Describe infrared spectroscopy.

Answer 1

Uses infrared radiation to increase the vibrational energy of covalent bonds in sample.
The frequency of infrared radiation absorbed by a covalent bond depends on:
- The atoms on either side of the bond
- The position of the bond in a molecule

Unit is Wavenumber (cm-1)

Question 2

Describe mass spectrometry.

Answer 2

Used to determine molecular mass of a compound.

Overview of the process:
- The substance is injected into the mass spectrometer
- The molecule loses an electron to form a positive ion
- Positive ion is displayed

Question 3

Describe fragmentation.

Answer 3

Molecules break up when they are bombarded with high energy electrons
Can be used to determine molecular structure
Fragmentation produces a positive fragment and a free radical. ONLY the positive fragment is detected.

Question 4

What is the equation for calculating the number of carbons in a substance?

Answer 4

n = (100 x abundance of M+1 ion) / (1.1 x abundance of M+ ion)

Round to the nearest whole number.