Organic analysis

Question 1

Name 3 analytical methods used to find the structure of complex molecules.

Answer 1

NMR Spectroscopy
Infrared Spectroscopy
Mass Spectrometry

Question 2

Why can NMR only be used on atoms with odd mass numbers (13C, 1H)?

Answer 2

These have the property spin, which is used in measuring the resonance of the atoms.

Question 3

Testing for an alkene

Answer 3

Shake with bromine water

Red brown colour should disappear

Question 4

Testing for halogenoalkane

Answer 4

1) add warm NaOH (aq)
2) acidify with HNO3
3) add AgNO3 (aq)
Precipitate of silver halogen forms

Question 5

Testing for alcohol

Answer 5

Add acidified potassium dichromate

Orange colours turns green

Question 6

Testing for aldehyde

Answer 6

Warm with Fehling’s/Tollens solution or add acidified potassium dichromate
Blue turns red
Silver mirror forms
Orange goes green

Question 7

Testing for a carboxylic acid

Answer 7

Add NaHCO3 (aq)
Bubbles form as CO2 is given off

Question 8

If the compound is acidic?

Answer 8

Carboxylic acid

Question 9

Is the compound is solid

Answer 9

Suggest long carbon chain or ionic bonding

Question 10

If compound is liquid

Answer 10

Suggests medium length carbon chair
Or polar
Or hydrogen bonding

Question 11

If compound is gas

Answer 11

Suggests short carbon chain

Little to no polarity

Question 12

Does compound dissolve in water

Answer 12

Suggests polar groups

Question 13

Does compound not dissolve in water

Answer 13

Suggests non polar groups

Question 14

Does compound burn with smoky flame

Answer 14

Suggests high C:H ratio, possibly aromatic

Question 15

Does compound burn with non smoky flame

Answer 15

Suggests low C:H ratio

Probably non-aromatic

Question 16

Why is TMS a suitable standard for NMR spec?

Answer 16

• easily removed due to low bp and volatile
• all hydrogen and carbons are in the same environment
• same environment produces one single large rush