Functional Groups and Preparations

Functional groups The functional group of alkanes is the C-C bond, the alkenes C=C bond and so on

Tetrahedral carbon compounds In addition to the alkanes the other tetrahedral compounds are the Chloroalkanes and the Alcohols

Chloroalaknes Historically surgery was extremely painful and people only underwent surgery if it was absolutely essential One of the early anaesthetics was Chloroform (CHCl3) (modern name tri-chloro methane) Chloroform is an example of a chloroalkanes Chloroalkanes are defined as compounds in which one or more of the hydrogen atoms in an alkane molecule have been replaced by a Chlorine atom

Chloroalkanes have the same basic tetrahedral shape as the corresponding alkanes and like alkanes they are all saturated compounds NB fig 22.1 p 341 for some common structures They are rarely found naturally and are usually synthesised in a laboratory

Properties of Chloroalkanes Most are liquid at room temperature Their main use is as solvents to remove oil and grease marks from machinery and in the dry cleaning of clothes Paint stripper contains dichloromethane (can you draw this???) They are insoluble in water (due to having very little polarity) They readily dissolve in non-polar solvents such as cyclohexane They are suitable solvents for things such as tippex but they cause damage to the ozone layer so scientists are looking for alternatives

Naming Chloroalkanes Find the parent chain of carbons and get the chain name (ie meth, eth, but) Determine the carbon the chlorine is attached to Determine the number of chlorines attached Eg. 2 –chlorobutane Eg. 2,2, 3 trichlorohexane

Alcohols The alcohol in alcoholic drinks is ethanol and is just one of many alcohols Methanol, ethanol, propanol, Butanol etc. All exist and are named according to the number of carbons in the parent chain One thing all alcohols have in common is their functional group which gives them their characteristic properties This is the Hydroxyl group (OH)

Remember Each carbon atom is basically tetrahedral shaped but the carbon with the OH group attached is v- shaped

12g 10cm3 10cm3 4cm3

Preparation of ethanal The first test tube should be discarded. Add small amounts of calcium carbide as it is very reactive with water

Preparation of ethanal Why is it necessary to turn off the Bunsen burner or heating element before the reaction is started? The reaction would become too vigorous, and some unreacted ethanol and other material is likely to be forced over into the conical flask. Once the mixture in the reaction vessel has been brought to the boil, further heating is not required as the oxidation of ethanol is an exothermic reaction, and gentle boiling can be maintained by regulating the flow from the dropping funnel.

Ketones Functional group of ketones is C-C=O C The only structural difference between aldehydes and ketones is that hydrogen atom in ketones is replaced by an alkyl group Rememeber AldHydes have the H the Hydrogen Because the carbonyl group has two alkyl groups attached it can never be at the end of the chain There are only two ketones on your course

Properties of ketones Higher boiling points than corresponding alkanes (due to presence of dipole-dipole forces) Boiling points are lower than those of corresponding alcohols due to lack of hydrogen bonding The polarity of the carbonyl group in lower members of the ketones causes them to be very soluble in water

Preparation of ethanoic acid Reflux (20 mins) 5g of sodium dichromate 5cm3 of sulphuric acid Cool flask with tap water

Preparation of ethanoic acid Mix 2 cm3 of ethanol and 10 cm3 of deionised water in the dropping funnel. 2.Add the solution from the dropping funnel dropwise down the condenser, while swirling the contents of the flask and cooling it if necessary to prevent too vigorous a reaction.

Cool the apparatus, dismantle and rearrange for distillation

Preparation of ethanoic acid Round flask used instead of pear shaped

Precautions Reflux distillation involves condensing the vapour from a boiling liquid in such a way as to return the condensed material to the reaction vessel. In this way a reaction may be carried out at quite a high temperature while preventing the loss of any of the reactants or products.

Esters

Esters are prepared in lab by the reaction between an alcohol and a carboxylic acid

The lower members of the ester family are volatile liquids with pleasant fruit smells.They give scent to fruit and flowers

Uses of organic acids Esters are used as artificial perfumes or scents as they emit a sweet smell. Esters are used in making artificial food flavours that are added in many edible items like ice creams, soft drinks, sweets, etc. Esters are used as industrial solvents for making cellulose, fats, paints and varnishes. Esters are used as solvents in pharmaceutical industries.  Esters are used as softeners in plastic industries and molding industries

3 fatty acids and glycerol

Practical set up Reflux Distillation

Saponification

Soap

Aromatic Cmpounds

Aromatic compounds are compounds that contain a benzene ring structure in their molecules Benzene is planar Benzene is non polar as there is a small electronegativity difference between hydrogen and carbon It was traditionally used as a solvent but was found to be carcinogenic so methyl benzene (toluene is now used instead) Would you predict it would be soluble in water or cyclohexane?

Organic Natural products

Many organic compounds are found in nature and are referred to as “natural products” Examples include caffeine, benzaldehyde (in almonds), nicotine, quinine and limonene 19th century mainly concerned with finding ways to isolate useful compounds such as morphine Now it is possible to work out the molecular structures and synthesize these in the laboratory

Steam distillation This is a method of extracting oils from plants It involves distillation in a current of steam It is very important to avoid too high a temperature as the oil may become damaged If the oil and water separate naturally they can be isolated using a tap funnel If an emulsion is obtained (where the oil drops are dispersed throughout the water) then an organic solvent that will dissolve the oil but not the water needs to be used

The organic solvent can be separated from the water with a tap funnel The organic solvent may then be evaporated and a pure sample of the oil remains