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Paper 2 Matter and Materials

Organic Molecules
Structure and Physical Property Relationships

Recognise and apply to particular examples (for compounds listed previously) the relationship between:

physical properties

melting points
boiling points
vapour pressure
viscosities

and intermolecular forces

hydrogen bonding
van der Waals

physical properties

melting points
boiling points
vapour pressure
viscosities

and number and type of functional groups

physical properties

melting points
boiling points
vapour pressure
viscosities

and chain length

physical properties

melting points
boiling points
vapour pressure
viscosities

and branched chains

SUBSTITUTION, ADDITION and ELIMINATION REACTIONS
ADDITION REACTIONS
Unsaturated compounds (alkenes, cycloalkenes, alkynes) undergo addition reactions.

Hydrohalogenation
Addition of HX to an alkene

eg.
Reaction conditions:
HX (X=Cl, Br, I)added to alkene
no water must be present
(During addition of HX to unsaturated hydrocarbons, the H atom attaches to the C atom already having the greater number of H atoms
The X atom attaches to the more substituted C atom

Halogenation
Addition of X₂ (X =Cl, Br) to alkenes

eg:
Reaction conditions
X₂ is added to alkene

Hydration
Addition of H₂O to alkenes

eg:
Reaction conditions
H₂O in excess
a small amount of HX or other strong acid H₃PO₄ as catalyst
(during addition of H₂O to unsaturated hydrocarbons, the H atom attaches to the C atom already having the greater number of H atoms. The OH group attaches to the more substituted C atom

Hydrogenation
Addition of H₂ to alkenes

eg.
Reaction conditions
alkene dissolved in a non polar solvent with the catalyst (Pt, Pd or Ni) in a H₂ atmosphere
Addition of H₂ to alkynes
eg.
Reaction conditions
akyne dissolved in a non polar solvent with Pt, Pd or Ni as catalyst in a H₂ atmosphere

ELIMINATION REACTIONS
Saturated compounds (haloalkanes, alcohols, alkanes) undergo elimination reactions

Dehydrohalogenation
Elimination of HX from a haloalkane

eg.
Reaction conditions
heat under reflux (vapours condensate and return to reaction vessel during heating) in a concentrated solution of NaOH or KOH in pure ethanol as the solvent
i.e. hot ethanolic NaOH/KOH
(If more than 1 elimination product is possible, the major product is the one where the H atom is removed from the C atom with the least number of H atoms)

Dehydration of Alcohols
Elimination of H₂O from an alcohol

eg.
Reaction conditions
Acid catalysed dehydration - heating of alcohol with an excess of concentrated H₂SO₄ or H₃PO₄
Gaseous alkenes eg. ethene can be produced easier when ethanol vapour is passed over heated Al₂O₃ powder.
(If more than one elimination product is possible, the major product is the one where the H atom is removed from the C atom with the least number of H atoms

Cracking of Hydrocarbons
Breaking up large hydrocarbons molecules into smaller and more useful bits.

Reaction conditions
High pressure and temperatures without a catalyst (thermal cracking)
OR
Lower temperatures and pressures in the presence of a catalyst (catalytic cracking)

SUBSTITUTION REACTIONS
Interconversion between alcohols and haloalkanes

Reactions of HX with alcohols to produce haloalkanes:

Reaction conditions: Tertiary alcohols are converted into haloalkanes using HBr or HCl at room temperature
eg.
Treat primary and secondary alcohols with concentrated H₂SO₄ and solid NaBr (or KBr).
The H₂SO₄ and solid NaBr reacts to form HBr:

The HBr reacts with the alcohol to form the bromoalkane.
eg.

Reaction of bases with haloalkanes (hydrolysis) to produce alcohols

eg.
Reaction conditions
Haloalkane dissolved in ethanol before treatment with aqueous sodium hydroxide and warming of the mixture:
the same hydrolysis reaction occurs more slowly without alkali, i.e.
H₂O added to the haloalkane dissolved in ethanol

Haloalkanes from alkanes

reaction conditions:
X₂ (X = Cl, Br) added to alkane in the presence of light or heat