Chapter 29 - Chromatography and spectroscopy

Question 1

What does thin layer chromatography do?

Answer 1

Shows how many components are in a mixture

Question 2

How do you set up a TLC plate?

Answer 2

A thin sheet of plastic or glass coated with silica

Question 3

What is the stationary phase in TLC?

Answer 3

The adsorbent

Question 4

What is adsorption?

Answer 4

Silica holds the different compounds in the mixture to its surface

Question 5

How do you calculate the retention factor?

Answer 5

Distance moved by component / distance moved by solvent

Question 6

What is the stationary phase in gas chromatography?

Answer 6

A high boiling liquid adsorbed onto a solid support

Question 7

What is the mobile phase in gas chromatography?

Answer 7

An inert gas carrier

Question 8

Process of gas chromatography

Answer 8

Mixture is injected into gas chromatograph
Gas carrier carries mixture through stationary phase
Components slow down
Components are separated depending on their solubility in the stationary phase

Question 9

What does the peak integration show us?

Answer 9

The concentrations of components in a sample

Question 10

How to test for a carbonyl

Answer 10

Add 2,4-dinitrophenylhydrazine and an orange precipitate will occur

Question 11

How to test for an aldehyde

Answer 11

Add Tollen’s reagent and warm

A silver mirror effect occurs

Question 12

How to identify a carboxylic acid

Answer 12

Add sodium carbonate and it will effervesce

Question 13

What can NMR be used to identify?

Answer 13

Isotopes with an odd number of nucleons

Question 14

What is resonance?

Answer 14

A strong magnetic field and radiation allow the nucleus to absorb so much energy that the electrons flip between spin states

Question 15

What chemical is used as the standard for chemical shifts?

Answer 15

Tetramethylsilane

Question 16

What is a deuterated solvent?

Answer 16

The 1H atoms have been replaced by 2H atoms (deuterium)

Question 17

Why are chemicals deuterated?

Answer 17

Deuterium produces no NMR signal

Question 18

What two pieces of information can be deduced from a carbon NMR spectrum?

Answer 18

The number of different carbon environments

The different types of carbon environment

Question 19

What will carbon atoms in different environments do?

Answer 19

Absorb radiation at different chemical shifts

Question 20

What information can be deduced from proton NMR?

Answer 20

The number of each type of proton environment

The number of each type of proton

Question 21

What does it mean when two protons are equivalent?

Answer 21

They will absorb at the same chemical shift

Question 22

What does the integration trace on a proton NMR tell you?

Answer 22

The number of protons responsible for each peak

Question 23

What is the n+1 rule?

Answer 23

For a proton attached to carbon atom with n protons, the number of peaks in the splitting pattern will be n+1

Question 24

Why is it difficult to identify NH groups and OH groups from a spectrum?

Answer 24

The peaks are broad and of variable chemical shift

Question 25

How are Oh and NH groups identified from a spectrum?

Answer 25

NMR is run as normal
D2O is added and the spectrum repeated
Deuterium replaces the OH and NH groups
As deuterium doesn’t absorb in the range we study, the OH peak essentially disappears