Revision on organic synthesis 1

1. Functional Groups and Organic Synthesis REVISION

Monday, 06 April 2026
Functional Groups and
Organic Synthesis
REVISION

2. Assessment Criteria

Monday, 06 April 2026
Assessment Criteria
Explain the usefulness of some reactions for the characterisation of organic
compounds or specific functional groups.
Identify compounds containing specific functional groups and identify
compounds by means of chemical and physical tests.
Identify compounds by means of chemical and physical tests.
Suggest structures for unknown compounds based on chemical tests.
Solve problems in synthesis using a synoptic knowledge of the organic
chemistry learned in the whole course.

3. Alkene

Describe how you would test for
alkenes.
TEST: Add bromine water to the sample.
OBSVERVATION: Bromine is decolourised. From To
Alkene
• Bromine/CCl4
"instant" decolourisation
• Potassium permanganate (cold, dilute,
alkaline)
From
To

4. Alkyl Halide

Describe how you would test the
presence of halogenoalkane.
TEST:
Add silver nitrate to the sample.
OBSVERVATION: If a halide is present a precipitate is formed.
Cl - white, Br – cream I - yellow
• AgNO3/EtOH
RX + AgNO3 RONO2 + AgX(s)
precipitate
What further test can we do on the products?
Add drops of ammonia solution - Cl dissolves readily
- Br partially soluble (in concentrated NH3(aq) only)
- I insoluble

5. Alcohol

Describe how you identify the different classes of alcohols.
• TEST Add acidified dichromate solution that is clear orange.
• OBSERVATION Expected observation to dark green solution indicates 1° or 2° alcohol
X
• GENERAL TEST FOR ALCHOHOL Add Na metal to the sample
• OBSERVATION
Bubbles are formed (due to H2 gas - can be further
tested using a lighted splint that produces a popping sound

6. -OH Group

Reaction with phosphorus (V) chloride, PCl5
Gas produced (HCl)
• forms white fumes with
NH3
• Turns blue litmus to red
• Reaction can occur with
water and carboxylic
acid, too

7.

Aldehyde and Ketones
Test 1
Both positive to 2,4-DNPH test
– gives yellow (orange) ppt
Test 2
Test 3
Dichromate test
Fehling’s Test
Tollens’ Test
Heat with ORANGE
acidified Cr2O72-
Heat with BLUE alkaline
Cu2+ ( + NaOH)
Heat with COLOURLESS
alkaline Ag+ ( + NH3)
BLUE SOLN BRICK-RED
PPT [Cu2O(s)]
COLOURLESS SOL’N
SILVER MIRROR [Ag(s)]
For Aldehyde :
ORANGE GREEN
SOL’N [Cr3+(aq)]
Cu(+2) (+1)
Cr(+6) (+3)
Ag(+1) (0)
ALDEHYDE IS OXIDISED TO THE CARBOXYLIC
ACID.
For Ketone :
Remains ORANGE
Remains BLUE
Remains COLOURLESS

8. Aldehydes

Describe the test of aldehydes using
Tollens’ Reagent.
TEST: Add aldehydes to the Tollens’ reagent and warm
OBSERVATION: silver mirror/shiny or gray precipitate is formed
• Silver mirror test /Tollens’ Reagent
RCHO + 2[Ag(NH3 )2]+ + 2OH-
RCOOH + 2 Ag + H2O + 4NH3

9. Fehling’s solution

Describe the test of aldehydes
using Fehling’s solution.
For distinguishing aldehydes from ketones
Test: Add drops of Fehling’s solution to the sample and
heat gently.
Observation: If aldehyde is present the blue solution forms
brick red precipitate.

10. Methyl alcohol and methyl ketone

What is iodoform test?
Used to check the presence of a methyl group
attached to a carbonyl or alcohol carbon R-CO-CH3
Iodoform test
Yellow ppt
only for R-CHOH-CH3
And for methyl ketones
O
R-C-CH3
yellow precipitate

11. Carboxylic acid

How would you test for
carboxylic acid?
TEST: Add bicarbonate or a carbonate or Na metal
OBSERVATION: bubbling or fizzing; effervescence
due to formation of CO2 (if carbonate
or bicarbonate is used)
Complete the equation below
2CH3COOH + Na2CO3 2CH3COONa + H2O + CO2
CH3COOH + NaHCO3 CH3COONa + H2O + CO2
CH3COOH + Na CH3COONa + ½H2

12. Organic Synthesis (aliphatic)

Monday, 06 April 2026
Organic Synthesis (aliphatic)
You need to know your aliphatic organic chemistry reactions
Haloalkane
Dihaloalkane
X2 + 20°C
Steam, H3PO4 catalyst, 60atm, 300°C
Alkene
Alcohol
Alkane
Conc H2SO4 / H3PO4 heat
K2Cr2O7, H2SO4 heat 1°
alcohol in distillation kit
Carboxylic
Acid
NaBH4 in methanol
and water
Aldehyde
K2Cr2O7, H2SO4 heat
2° alcohol in reflux kit
NaBH4 in
methanol and
water
Ketone

13. Organic Synthesis (aliphatic)

Monday, 06 April 2026
Organic Synthesis (aliphatic)
You need to know your aliphatic organic chemistry reactions
Primary
Amine
NH3 + heat
LiAlH4 +
dilute H2SO4
Haloalkane (from
previous slide)
NH3 + heat
KCN, H2SO4 @ 20°C
Hydroxynitrile
2° / 3° amines and
quaternary ammonium salts
Nitrile
Primary
Amide
N-substituted
Amide
Carboxylic Acid (from previous slide)
H2O @ 20°C
Acid Chloride
/ Anhydride
Amine @ 20°C
Aldehyde /
Ketone (from
previous
slide)
Dilute H2SO4, H2O,
reflux and catalyst OR
dilute NaOH, reflux
Conc H2SO4,
alcohol, heat
and catalyst
Ester

14. Organic Synthesis (aromatic)

Monday, 06 April 2026
Organic Synthesis (aromatic)
NITRATION
Conc. H2SO4 and
HNO3, < 55°C
Benzene
Nitrobenzene
REDUCTION
Conc. HCl, Sn
& reflux.
Add NaOH
Phenylamine
NH2
CH3COCl @
RTP
O
R
Phenylketone
ACYLATION
RCOCl AlCl3 catalyst, reflux,
anhydrous conditions
NO2
C
N-phenylethanamide
NHCOCH3

15. Organic Synthesis

Monday, 06 April 2026
Organic Synthesis
Chemists use organic synthesis to make drugs, however they are looking to
make them cost effective, safe and have minimal environmental impact
Chemists try to use
synthetic routes using
starting materials that are
safe and have low toxicity
levels to living things.
Waste reduction is important too.
Reactions that have a high atom economy
and high percentage yield are preferred.
Synthetic processes that have less steps
generally have less waste and are more
efficient.
Solvents are sometimes used in chemical reactions however they are
often flammable and toxic and increase waste. Chemists try to develop
synthetic routes where solvents are not used or are minimized.