Alkenes and Alcohols AS AQA Unit 2

Alkenes, 

• Alkenes are unsaturated molecules (they consist of c=c double bonds).
• The name of the first three alkenes are: Ethene, Propene, Butene,
• They have a general ormular of CnH2n

Sterioisomerism,

E-Z sterioisomerism,

e.g.,

e-but-2-ene <-- this is when the hydrogens attached to the carbon on either end of the double bonded carbon are on OPPOSITE sides of the molecule. 

z-but-2-ene <-- this is when the hudrogens attached to the carbon on either ond of the double bonded carbon are on the SAME side of the molecule. 

Sterioisomerism continues:

Definition:

Compounds that have the same sturcutal formular but the bonds are arranged differently in the space.

Electrophillic Addition

In this, the unsaturated alkenes become saturated. in other words the c=c double bonds get broken into c-c single bonds. 

Electrophillic- electron rich! c=c are electron rich and so attract posotive atoms (electrophils)

Addition - forms one new molecule!

This can be done by using:

• Hydrogen Bromide HBr
• Sulphuric Acid H2SO4
• Bromine, Br2

HBr

form bromoalkanes.. This is the MECHANISM forming 2methyl-2-bromopropane A posotive carbon is the CARBOCATION!

.    

H2SO4

forms a alkyl hydrogensulphate...

MECHANISM:

Produces in this case ethyl hydrogensulphate. 

when H2O(warmed) is added to this is produces ethanol and H2SO4 again. 

Br2

Produces a dibromoalkane...

MECHANISM:

The originally brown bromine solution will now turn colourless as the unsaturated alkene is now saturated, has been made into in this case dibromoethane. 

Major and Minor Product...

Primary Carbocation: has one alkyl group attached to C+ (LEAST STABLE carbocation) 

Secondary Carbocation: has 2 alkyl groups attached to the C+

Tirtiery Carbocation: has 3 alkyl groups attached to the C+ (MOST STABLE carbocation)

Major Product is formed via the MOST STABLE carbocation

Minor Product is formed via the LEAST STABLE carbocation.

Direct Hydration...

e.g.

Ethene + H20 (300*C, 6.5x10^3kPa)-------> Ethanol

There is a presence of Phosphoric Acid (H3PO4)

ALCOHOLS!

Alcohols...

• General formular... CnH2n+1(OH)
• all contain a HYDROXYL
• first two alcohols are: Methanol, Ethanol 

• Alcohols - end in, -ol or Hydroxyl- always have an OH attached i.e. ETHANOL and HYDROXY PROPANOIC ACID.
• Aldehyde - end in -al, always have a double bonded oxygen =o attached and a hydrogen h- i.e ETHANAL
• Ketones - end in -one or oxo- have a double bonded oxygen only arrached o= i.e. PROPANONE and OXOBUTANOIC ACID
• Carboxylic Acid, end in -oic acid, always have a double bonded oxygen o= and an OH group on the end. i.e. ETHANOIC ACID

FERMENTATION:

• 35*C
• 1 atmosphoric pressure
• No oxygen
• Water
• Yheast ENZYME NATURAL CATALYST
• Batch Process
• Slow
• Impure product
• more for drinking
• Ethanol produced
• c6h12o6 ------> 2c2h5oh + 2co2

DIRECT HYDRATION: 

• 300*c
• 6.5X10^3 kPa
• steam
• phosphoric acid is catalyst
• more insustrial uses
• ethanol produced
• much pruer product
• c6h12o6 + h2o----> c2h5oh
• Continious process