Tetrahedral Carbons C3H8

C=O Planar Carbon CH3CHO

Addition Reactions Planar Tetrahedral

2 reactants making 1 product Addition as something will be added across the double bond

Double bonds are stronger than single bonds – so why do addition reactions happen so easily? Energy requird to break double bond Energy released when two single bonds formed Net release of energy meaning products more stable than reactants Need to know reaction with H2 and H2O Need to know mechanism with Br2, Cl2 and HCl

Bromine Mechanism Br – Br bond becomes polarised Heterolytic fission occurs Carbonium ion formation Br+ adds on to ethene, cyclic structure formed Attack on carbonium ion by bromide ion Final product is 1,2-dibromoethane Same mechanism for HCl and Cl2, but no ring structure, neither Cl nor H big enough to (stretch across)

Ionic Addition – Evidence for Called ionic addition as ions add across double bond and also carbonium ion formed Can be proven by adding bromine in water in presence of sodium chloride NaCl – 2 forms of evidence Chloride ion attacks carbonium ion forming 1-bromo-2-chloroethane Water molecule attacks carbonium ion forming 2-bromoethanol

Uses Must know uses for the products of the five reactions Additive Product and Use H2 Ethane - fuel HCl Chloroethane – solvent H2O Ethanol – solvent / additive for petrol Cl2 1,2 – dichloroethane – used to make vinyl chloride – PVC Br2 1,2 – dibromoethane – pesticide, insecticide Must know uses for the products of the five reactions Must be able to discuss hydrogenation of oils

Dairy products like butter and cream are mainly saturated – no double or triple bonds Margarine invented as alternative Edible oils are esters of long chain unsaturated carboxylic acids – lots of C=C Less damaging to health But oils not much use for spreading on bread But by adding H2 across some of the double bonds, oils could be changed into soft solids with low melting points – margarine Margarine is easier to spread than butter (lower melting point) It also contains less saturated fats that people worry about By controlling degree of H2 added, margarine can be made as soft or as hard as needed

Polymers Long chain molecules made by joining together (adding) many small molecules They consist of a repeating structure and can have a molecular mass of several thousand monomer + monomer +…. polymer Commonly known as plastics Examples include polythene, poly(propene), PVC, polyester, etc Draw out some structures from the book into your notes copy (pg 369/370).

Substitution Reactions Tetrahedral Tetrahedral Planar Planar

Need to know same mechanism for ethane Chlorine Mechanism Initiation UV light breaks down Cl2 into 2 Cl atoms Propagation A Cl atom attacks the CH4molecule to form HCl and a methyl free radical A methyl free radical attacks a Cl2 molecule to form ClCH3 and a Cl atom These two processes repeat continuously in a chain reaction Termination Free radicals and atoms combine with each other to stop reaction Need to know same mechanism for ethane

Free Radicals – Evidence for Called free radical substitution 2 forms of evidence Small amounts of ethane are found among the products – only can be formed when 2 methyl radicals bond If tetramethyl lead is added to reaction mixture, rate of reaction increased – Pb(CH3)4 feeds methyl radicals into system, speeding up propagation (Butane and tetraethyl lead when accounting for ethane mechanism)

Esterification Acid + Alcohol Ester + Water Ethanoic acid + Ethanol Ethyl ethanoate + water + + H2O In the presence of heat and concentrated sulphuric acid

Hydrolysis of Esters Ester + Water Acid + Alcohol Reverse of Esterification Called hydrolysis because ester REACTING WITH water Similar reaction happens with a base instead of water

Ester + Base Salt + Alcohol Called base hydrolysis of esters or saponification Soaps are long chain potassium / sodium salts of carboxylic acids -- mandatory exp + NaOH +

Elimination Reaction Tetrahedral Planar

Redox Reaction Tetrahedral Planar Planar Tetrahedral

Redox Reactions Recall from Chapter 15 that oxidation can be described by the gain of Oxygen Recall from Chapter 15 that reduction can be described by the gain of Hydrogen Therefore oxidation can also be described as the loss of hydrogen – dehydrogenation

Primary Alcohols Primary alcohols are oxidised to the corresponding aldehydes, which can be further oxidised to the corresponding carboxylic acids. Loss of H2 Gain of O K2Cr2O7 crystals turn from orange to green during process

Secondary Alcohols Secondary alcohols are oxidised to ketones, and no further Loss of H2

Reductions Carboxylic acids are reduced to the corresponding aldehydes and further to the corresponding alcohols – (opposite of oxidation) Loss of O Gain of H2

Facts Word aldehydes comes from alcohol dehydrogenation Oxidation of ethanol to ethanoic acid causes problems for wine producers – open wine can turn to dilute vinegar! Breathalyser test uses K2Cr2O7 crystals, extent to which the crystals turn green is a measure of concentration of alcohol in blood

tetrahedral planar

(a) Tetrahedral Tetrahedral Reactions as Acids (a) Tetrahedral Tetrahedral (b) Planar Planar

Acidic Nature Of Carboxylic Acids If something willingly loses a H+, than it is considered to be an acid OH group is polar enough that a H+ can be lost Alcohols have low tendency to lose H+, lower than water. Only react with very reactive metals Carboxylic Acids on the other hand are much more reactive Due to inductive effect in COOH group, the end H is very easily lost Carboxylate ion formed is very stable (electron delocalisation as with benzene) This stability is driving force behind losing of H+ Reacts as normal acid but much weaker than common lab acids

b) R e action of A c ids Magnesium Salt + H y drogen Mg A cid

Ester Ketones Alcohol Aldehyde Acid Alkenes Alkanes Polymers HCl H 2 /Ni Sodium Salt Cl U.V. light Ester Sodium Salt + A l cohol Na Acid Alcohol NaOH Al O 3 KEY Addition Reactions Substitution Reactions Redox Reactions Elimination Reactions Reactions of Acids Ketones H 2 O Alcohol Aldehyde Acid Oxidation Reduction Na Cr 7 and H + /Ni Magnesium Salt Sodium Salt Mg NaOH CO 3 Chloroalkanes Alkenes Alkanes Polymers Reduction H 2 /Ni Cl2 Br2 Bromoalkanes