Quick Notes - DSE Organic Chemistry
N. B.
The notes is only for quick reference. Not all contents for HKDSE are included.
A homologous Series - a group of carbon compounds with
same funcational group -> gives chemical properties to organic molecules
same general formula -> e.g. CnH2n+2 for alkanes, CnH2n for alkenes, CnH2n+1OH for alcohols, etc.
similar chemical properties (due to the same functional group)
gradual change of physical properties (due to change of molecular mass)
Alkane
- combustion (complete and incomplete)
- free radical substitution reactions with halogen (uv light or high T)
- 3 steps: Initiation, Propagation and Termination
Alkene [C=C]
- addition reaction with halogen (e.g. Br2 in organic solvent) -> from brown/orange to colourless
- oxidation reaction with acidified potassium permanganate (KMnO4/H+) -> from purple to
colourless
Alkanols (alcohols) [-OH]
Primary
Secondary
Tertiary
- 3 classes (primary 1o, secondary 2o & tertiary 3o)
- oxidation by K2Cr2O7/H+ to form aldehyde, ketone and carboxylic acid
- primary alcohol --> aldehyde --> carboxylic acid
- secondary alcohol --> ketone
- tertiary alcohol --> no reaction
- formed by reacting haloalkanes with NaOH(aq)
Alkanoic acids (carboxylic acids) [-COOH]
- can behave as a weak acid (pH < 7), e.g. ethanoic acid in vinegar
- formed by oxidation of primary alcohols
- can be reduced by LiAlH4 to form alcohol (*but not NaBH4 - weaker reducing agent)
Carboxylic acid
Carboxylate ion
Haloalkanes [-F, -Cl, -Br, -I, etc.]
- formed from alkanes (substitution with X2), alkenes (addition with HX or X2) and alcohols (with
PX3)
Aldehydes [-CHO]
- formed by oxidation of 1o alcohol
- low b.p. because of no H-bonds -> no H atoms attached to O atom (high electronegativity)
Ketones [C=O]
- formed by oxidation of 2o alcohol
- can be reduced by LiAlH4 or NaBH4
Esters [-COO-]
- fruity smell
- formed by reacting alcohol with carboxylic acid, conc. H2SO4 (catalyst) added
- linkage group in condensation polymer (polyester)
- hydrolysis (acid - reversible reaction or alkaline - irreversible reaction)
Unsubstituted amides [-CONH2]
- formation: carboxylic acid -> acid chloride -> unsubstituted amide (nitrogen atom connected to
one alkyl group only, and two H atoms)
- hydrolysis (acid - irreversible reaction, or alkaline - irreversible reaction)
Primary amines [-NH2]
- primary 1o: means nitrogen atom connected to one alkyl group only, and two H atoms
- is the functional group in one of the monomers in condensation polymeration to form nylon (the
other functional group needed is -COOH)
Isomers
Compounds with the same molecular formula but different structural formula (Structural) OR
different arrangements of atoms in space (Stereo)
Two types - Structural isomers & Stereoisomers
Structural isomers - 3 types, Chain, Position & Functional Group
Stereoisomers - 2 types, Cis-trans, Enantiomers (mirror images are not superimposable)
-cis
-trans
Enantiomers (with chiral carbon)
Inter-conversions of carbon compounds with different functional groups (Organic Synthesis)
Alcohols - a group of important intermediates
Formation of alcohols:
- Alkane / Alkene --X2(g)--> Haloalkane (RX) --NaOH(aq)--> Alcohols (ROH)
Oxidation of alcohols (with oxidizing agent like Cr2O72-/H+(aq)):
- Primary alcohols (ROH) --> Aldehydes (RCHO) --> Carboxylic acids (RCOOH)
- Secondary alcohols --> Ketones (RCOR’)
- Tertiary alcohols --> no further oxidation
Formation of esters and amides (condensation):
- Carboxylic acids (RCOOH) --R’OH, H+(aq) with heat--> Esters (RCOOR’)
- Carboxylic acids (RCOOH) --(1)PCl3, then (2)NH3--> Amides (RCONH2)
Important organic substances
(1) Acetylsalicylic acid (Aspirin)
contains a benzene ring, carboxyl group (-COOH) & ester group
medical application: relieve pain and prevent heart attack
side effect: stomach upset and cause increased bleeding
after alkaline hydrolysis with NaOH(aq):
- ester group -> hydroxyl (-OH) group
- carboxylic acid -> carboxylate ion (-COO-Na+)
after acid hydrolysis with H+(aq):
- ester group -> hydroxyl (-OH) group
- carboxylic acid -> no change
(2) Soapy and soapless detergent
- differences in manufacture (made from fats/oils [soapy] or petroleum [soapless])
- differences in structures (both have long hydrocarbon tails, but different ionic heads: soapy carboxylate ions & soapless - sulphate or benzenesulphonate)
- saponification: alkaline hydrolysis of animal fats or vegetable oils
(3) Polyamide
(Nylon) & polyester (PET)
- condensation polymerization, with elimination of small molecule (H2O)
Nylon
Poly(ethylene terephthalate) - PET