Alcohols

These have the ending-ol and if necessary the position number for the OH group is added between the name stem and the –ol If the compound has an –OH group in addition to otherfunctional groups that need a suffix ending then the OH can be named with the prefix hydroxy- If the re are two or more -OH groups then di, tri are used. Add the ‘e’ on to the stem name though eg propane1,2,3triol

All the H-C-H bonds and C-C-O are 109.5o (tetrahedral shape), because there are 4 bonding pairs of electrons repelling to a position of minimum repulsion. The H-O- C bond is 104.5o (bent line shape), because there are 2 bonding pairs of electrons and 2 lone pairs repelling to a position of minimum repulsion. Lone pairs repel more than bonding pairs so the bond angle is reduced.

The alcohols have relatively low volatility and high boiling points due to their ability to form hydrogen bond between alcohol molecules. Smaller alcohols can dissolve in water because they can form hydrogen bonds to water molecules.

Primary alcohols are alcohols where 1 carbon is attached to the carbon adjoining the oxygen.

Secondary alcohols are alcohols where 2 carbon are attached to the carbon adjoining the oxygen.

Tertiary alcohols are alcohols where 3 carbon are attached to the carbon adjoining the oxygen

Potassium dichromate K2Cr2O7

Reaction: primary alcohol —> aldehyde Reagent: potassium dichromate (VI) solution and dilute sulfuric acid. Conditions: (use a limited amount of dichromate) warm gently and distil out the aldehyde as it for

An aldehyde’s name ends in–al. It always has the C=O bond on the first carbon of the chain so it does not need a number in its name When writing the formulae of aldehydes in a condensed way write CHO and not COH e.g.CH3CH2CHO

CH3CH2CH2OH + [O] —> CH3CH2CHO + H2O [O] represents O from oxidising agent.

Observation: the orange dichromate ion (Cr2O7 2-) reduces to the green Cr 3+ ion

In general used as separation technique to separate an organic product from its reacting mixture. In order to maximise yield collec e collection flask can be cooled in ice to help improve the yield of distillate ted, only collect the distillate at the approximate boiling point of the desired aldehyde and not high

The bulb of the thermometer should be at the T junction connecting to the condenser to measure the correct boiling point The water goes in to the bottom of the condenser to go against gravity. This allows more efficient cooling and prevents back flow of water.

Electric heaters are often used to heat organic chemicals. This is because organic chemicals are normally highly flammable and could set on fire with a naked flame.

Reaction: primary alcohol —> carboxylic acid Reagent: potassium dichromate(VI) solution and dilute sulfuric acid Conditions: use an excess of dichromate, and heat under reflux: (distil off product after the reaction has finished)

H3CH2CH2OH + 2[O] —> CH3CH2COOH + H2O propan-1-ol —> propanoic acid

Reflux is used when heating organic reaction mixtures for long periods. The condenser prevents organic vapours from escaping by condensing them back to liquids.

Never seal the end of the condenser as the build up of gas pressure could cause the apparatus to explode. This is true of any apparatus where volatile liquids are heated including the distillation set up.

To prevent vigorous, uneven boiling by making small bubbles form instead of large bubbles.

It’s important to be able to draw and label this apparatus accurately. • Don’t draw lines between flask and condenser. • Don’t have top of condenser sealed • Condenser must have outer tube for water that is sealed at top and bottom • Condenser must have two openings for water in and out that are open

Reaction: secondary alcohol —> ketone Reagent: potassium dichromate(VI) solution and dilute sulfuric acid. Conditions: heat under reflux

Ketones end in-one When ketones have 5C’s or more in a chain then it needs a number to show the position of the double bond. E.g. pentan-2-one

There is no further oxidation of the ketone under these conditions

Tertiary alcohols cannot be oxidised at all by potassium dichromate: This is because there is no hydrogen atom bonded to the carbon with the -OH group