Chapter 29 - Chromatography And Spectroscopy

Question 1

What makes up a TLC plate

Answer 1

Plastic/ glass sheet sprayed with solid silica

Question 2

Adsorption

Answer 2

How the solid silica holds substances to its surface in TLC

Question 3

Uses of TLC

Answer 3

Drug analysis and forensic science

Question 4

Rf value formula

Answer 4

Distance by solute/ distance by solvent

Question 5

How to view invisible solvents of TLC

Answer 5

Spray with developing agent

Question 6

TLC: retention

Answer 6

Interaction between solute and stationary phase
Polar solute and polar stationary phase = strong adsorption more retention so lower rf

Question 7

TLC: solubility

Answer 7

Between solute and mobile phase
Polar solvent non polar solute spends more time adsorbed to stationary phase so lower rf

Question 8

Gas chromatography stationary phase

Answer 8

High boiling liquid adsorbed to solid support

Question 9

Gas chromatography mobile phase

Answer 9

Inert carrier gas (helium)

Question 10

Retention time

Answer 10

How long substance stays in gas chromatography thing
Polar stationary phase, non polar solute has lower retention time

Question 11

Test for alkenes

Answer 11

Mix with bromine water, alkene, cause rapid decolourisation of bromine water
Colour change: orange to colourless

Question 12

Test for Haloalkanes

Answer 12

Add aqueous silver nitrate - forms a precipitate
Chloro: white
Bromo: cream
Iodo: yellow

Question 13

Test for primary secondary alcohol and aldehyde

Answer 13

Add acidified potassium dichromate (VI) and heat
Colour change from Orange to Green

Question 14

Test for carboxylic acid

Answer 14

Add a carbonate such as sodium carbonate effervescence occurs

Question 15

Carbon 13 NMR number of carbon environments

Answer 15

The number of peaks

Question 16

Carbon 13 NMR type of carbon environment

Answer 16

The chemical shift

Question 17

Proton number of proton environment

Answer 17

Number of peaks

Question 18

Proton, NMR number of protons in each environment

Answer 18

Integration trace/ratio of relative peak areas

Question 19

Proton NMR n +1 rule

Answer 19

n = no. H+ on adjacent carbons
+1 for (H+)s of environment

Question 20

What is TMS

Answer 20

Reference compound
Has 12 protons in the same environment, so the most shielded they can possibly be
Assigned a chemical shift of 0 ppm

Question 21

Advantages of TMS as a reference compound

Answer 21

Chemically inert
Soluble in most organic solvents

Question 22

Proton, NMR, shielding

Answer 22

Electron shield protons from external magnetic fields decrease in chemical shift

Question 23

Proton, NMR deshielding

Answer 23

Electronegative groups, attract electrons away from the protons decreasing shielding equals increased chemical shift

Question 24

Problem with OH and NH on proton NMR

Answer 24

The protons aren’t bonded to a carbon: hard to identify as they have a broad/ variable chemical shift

Question 25

Proton exchange for hydroxyl and Amine groups

Answer 25

Run anymore as normal
Add dueterated solvent
Run NMR again
Any peaks that disappear, the second time are OH/NH groups

Question 26

How old is proton exchange with deuterium work

Answer 26

It’s exchanges and replaces labile protons of OH/NH

Question 27

Why don’t deuterated solvents show on proton NMR spectra

Answer 27

D is and isotope of H and doesn’t create a chemical shift