F UNCTIONAL G ROUPS AND P REPARATIONS

F UNCTIONAL GROUPS  The functional group of alkanes is the C-C bond, the alkenes C=C bond and so on

T ETRAHEDRAL CARBON COMPOUNDS  In addition to the alkanes the other tetrahedral compounds are the Chloroalkanes and the

Alcohols

C HLOROALAKNES

 Historically surgery was extremely painful and people only underwent surgery if it was absolutely essential  One of the early anaesthetics was Chloroform (CHCl 3 ) (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Chloroalkanes are defined as compounds in which one or more of the hydrogen atoms in an alkane molecule have been replaced by a Chlorine atom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

P ROPERTIES OF C HLOROALKANES      

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

N AMING C HLOROALKANES      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

A LCOHOLS     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)

R EMEMBER  Each carbon atom is basically tetrahedral shaped but the carbon with the OH group attached is v shaped

4cm 3 12g 10cm 3 10cm 3

P REPARATION OF ETHANAL   The first test tube should be discarded.

Add small amounts of calcium carbide as it is very reactive with water

P REPARATION 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.

K ETONES  Functional group of ketones is C-C=O The only structural difference between aldehydes and ketones is that hydrogen atom in ketones is replaced by an alkyl group C 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

P ROPERTIES 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

P REPARATION OF ETHANOIC ACID Reflux (20 mins) 5g of sodium dichromate 5cm 3 of sulphuric acid Cool flask with tap water

P REPARATION OF ETHANOIC ACID 1. 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

P REPARATION OF ETHANOIC ACID Round flask used instead of pear shaped

P RECAUTIONS   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.

E STERS

E STERS 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

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Esters are used as artificial perfumes or scents as they emit a sweet smell.

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Esters are used in making artificial food flavours that are added in many edible items like ice creams, soft drinks, sweets, etc.

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Esters are used as industrial solvents for making cellulose, fats, paints and varnishes.

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Esters are used as solvents in pharmaceutical industries.

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Esters are used as softeners in plastic industries and molding industries

3 fatty acids and glycerol

Reflux

Practical set up

Distillation

S APONIFICATION

S OAP

A ROMATIC C MPOUNDS

 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?

O RGANIC N ATURAL 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 19 th 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

S TEAM 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