Organic Analysis & Structure Determination Flashcards
What is the test for sulphate ions?
Barium chloride solution acidified with dilute hydrochloric acid.
(BaCl2/HCl)
What is the test for distinguishing between 1°/2° alcohols and 3° alcohols?
Test: acidified postassium dichromate (VI) (K2Cr2O7/H2SO4)
- 1°/2°orange to green
- 3° no visible change
What are the following alcohols oxidised to:
- 1°
- 2°
- 3°
- 1° Aldehyde then carboxylic acid
- 2° Ketone
- 3° Isn’t oxidised
How can aldehydes and ketones be distinguished from one another?
Tollen’s Reagent [diamminesilver (I)]:
- Aldehyde: Silver mirror
- Ketone: No visible change
OR
Fehling’s solution:
- Aldehyde: Brick red precipitate
- Ketone: No visible change
How can halide ions in solution be distinguished?
Test: acidified silver nitrate (AgNO3/HNO3)
- F- - no precipitate
- Cl- - white precipitate
- Br- - cream precipitate
- I- - yellow precipitate
How can isomer X be identified using its infrared spectra?
Compare the fingerprint region
Match with a known sample from a database of spectra
Why does bromine react with the double bond in an alkene?
The double bond is a region of high electron density It induces a dipole in the bromine molecule
(repels electrons in the bromine)
How could liquid X be purified?
Fractional distillation
OR
Column chromatography
What is the test for an alkene?
Add bromine water (Br2(aq))
Decolourises in presence of an alkene (orange to colourless)
What is the test for haloalkanes?
Add NaOH and warm
Acidify with HNO3 and add AgNO3
The relevant coloured precipitate will form (depends on halogen)
What is the test for carboxlic acids?
Add NaHCO3
Effervesces
What is the test for acyl chlorides?
Add AgNO3(aq)
A white precipitate will form
What is represented by the peak of highest abundance on a mass spectra?
The most stable fragment
What is the fragmentation equation of a molecular ion?
M+• → X+ + Y•
Which irons are most stable?
Tertiary carbocations
The acylium ion [R-C=O]+
How can the identity of a compound be confirmed using its infrared spectra?
Compare the fingerprint region to a database of known spectra
Find an exact match
What is chromatography used for?
Separate out substances
Why does the retention time of molecules vary?
Different molecules have different affinities to the stationary and mobile phases
Those that adsorb more to the stationary phase have a longer retention time
Those that are more soluble have a shorter retention time
How can a substance be separated and identified using chromatography?
Dissolve in a suitable solvent
Pour the solution into a column
The most soluble substance will have the shortest retention time
Compare the retention time with the standard retention time to identify the substance
How can substances be more effectively separated by chromatography?
Increase the retention time
What element is used at the standard in nmr?
Trimethylsilane (TMS)
Si(CH3)4
What is a suitable solvent for proton nmr?
Tetrachloromethane or deuterated trichloromethane
(CCl4 or CDCl3)
The solvent must be proton free
