Unit 4- Spectroscopy

Question 1

How are

a) Infrared in analysis
b) microwave for heating
c) radio waves in NMR
d) Ultraviolet in initiation reactants

used?

Answer 1

a) causes bonding and stretching of bonds
b) causes molecules with polar bonds to rotate faster
c) affect the way in which nuclei spin in a strong magnetic field
d) causes covalent bonds to break homolitically forming radicals

Question 2

Explain how a hydrogen nuclei can absorb radio waves?

Answer 2

Hydrogen nuclei will normally spin.
this results in a weak magnetic field.
when lined up against a strong magnetic field, the nucleus magnetic field lies parallel or at right angle to the stronger magnetic field.
This causes a energy difference.
The nuclei then absorbs radio waves and move to a higher state

Question 3

Explain Low and High resolution NMR spectra

Answer 3

Low resolution - peaks due to different chemical environments
High resolution - Causes spin coupling and splitting of the peaks due to adjacent carbons altering the magnetic field
use the (n+1) rule to the adjacent carbon

Question 4

explain Chromotography

Answer 4

• all forms have a stationary phase
• passed through stationary phase through an eluent (gas or liquid)
• Different components travel through the stationary phase at different speeds and therefore seperated

Question 5

what is GLC and explain it

Answer 5

Gas-liquid chromatography:
sample of liquid mixture being injected into a column that is temperature controlled in an oven.
The sample evaporates and passes through the column by flow of nitrogen gas or another inert gaseous eluent.
The gases pass through a detector.
identity of components found by measuring their infrared spectra and comparing to a database

Question 6

What is HPLC and explain it

Answer 6

High- performance liquid chromatopgraphy:
consist of column packed with a solid (stationary phase)
The sample is dissolved in a suitable solvent and placed at the top of column
The liquid eluent is forced through the column under high pressure ( moving phase)
Time taken for the component to pass through is the retention time
The high pressure decreases the amount they spread out from diffusion
Gives a higher resolution
components then measured through an infra red spectra