- Created by: George
- Created on: 10-05-11 15:16
Structure of Benzene C6H6: There are 2 structures: the Kelkule structure and the Delocalised Pi structure.
- The Kelkule structure has 2 types of bond.
- The delocalised Pi System has 1 type of bond.
- Delta H of benzene is -208 not -360 that the Kelkule structure suggests.
- Benzene does not react with Bromine as there is insufficient electron density to polarise the Br-Br bond. A halogen carrier is needed. The Kelkule structure has 3 double bonds therefore sufficient electron density to react, without a catalyst.
F324: Electrophilic Substitution and Phenol
Mononitration: C6H6 + HNO3 >>> C6H5NO2 + H2O
Halogenation: C6H6 + Cl2 >>> C6H5Cl + HCl
Phenol: C6H5OH. As it has a benzene ring and hydroxy group its chemistry can be treated in 2 parts.
1) Reactions of the OH group: Phenol loses the proton of its OH group more easily because of the presence of the Benzene ring. It weakens the OH bond. Thus phenol acts as a proton donor.
2) Reactions of the Benzene group: Lone pairs of oxygens on the OH group can be delocalised on the benzene ring. This increases electron density on the ring making benzene more reactive. Hence it reacts more readily than benzene due to the increased electron density. No halogen carrier.
Uses: Phenol is used in plastics; resins in paints, antiseptics and disinfectants.
- Aldehydes: end in al H-C=O
- Ketones: end in one -C=
- Aldehydes: are prepared by the oxidation of primary alcohols using acidified potassium dichromate.
- CH3CH2CH2CH2OH + (O) >>> CH3CH2CH2CHO + H20
- Ketones: are prepared by the oxidation of secondary alcohols using acidified potassium dichromate.
- CH3CH2CH(OH)CH3 + (O) >>> CH3CH2COCH3 + H20
Reduction: Reagent is sodium borohydroxide - NaBH4 in water.
- Aldehydes are reduced to primary alcohols. RCHO + 2(H) >>> RCH2OH
- Ketones are reduced to secondary alcohols. RCOR' + 2(H) >>> RCH(OH)R'
F324: Distinguishing and identifying carbonyl comp
Identifying Test: Add 2,4 DNPH
- Aldehydes: Orange crystalline ppt, characteristic melting point and unique data.
- Ketones: Orange crystalline ppt, characteristic melting point and unique data.
Distinguishing Test: Ammonical Silver Nitrate (Tollens reagent).
- Aldehydes: Oxidised to a carboxylic acid. Silver mirror forms. RCHO + (O) >>> RCOOH.
- Ketones: No reaction.
Add Potassium Dichromate:
- Aldehydes: Oxidised to a carboxylic acid. Orange to Green.
- Ketones: No reaction - stays orange.
F324: Carboxylic Acids
CnH2nO2. Short-Chain carboxylic acids are soluble with water as they form hydrogen bonds with water.
- Acids: In the carboxyl group the 2 electronegative oxygens pull electrons towards them, weakening the OH bond. Therefore proton donors.
- Metals: 2CH3COOH + Mg >>> (CH3COO)2Mg + H2
- Alkalis: CH3COOH + NaOH >>> CH3COO(-)Na(+) + H20
- Carbonates: 2CH3COOH + Na2CO3 >>> 2CH3COO(-)Na(+) + CO2 + H2O
- Esterification: Carboxylic acid + Alcohol <-> Ester + Water
- Acid Anhydride: Acid Anhydride + Alcohol <-> Ester + Carboxylic Acid
CnH2nO2. However there is no absorption bond at 2500-3000 cm(-1). Esters are named according the acid and alcohol from which they are prepared. Alcohol part 1st and acid part 2nd.
Acid + Alcohol <-> Ester + Water
Fatty Acids, Fats and Oils:
Fats are esters of long-chain carboxylic acids (fatty acids) and the alcohol glycerol. These are called triglyceride's. The greater the number of the C=C chains, the lower the melting point. Unsaturated fatty acids make up triglyceride's found in animal fats.
Fatty Acids and Our Health:
Trans fatty acids are formed when manufacturers add hydrogen to vegetable oil. (Hydrogenation.). These are associated with bad cholesterol.
When fats are hydrolysed by alkalis, salts of long chain fatty acids (soaps) are formed: saponifcation.
- Acid: CH3COOC2H5 + H20 <-> CH3COOH + C2H5OH
- Alkali: CH3COOC2H5 + OH(-) <-> CH3COO(-) + C2H5OH
- Transesterification reactions between triglyceride's + alcohol <-> esters + glycerol.
F324: Nitrogen Compounds
Amines: They are derivatives of ammonia (NH3). Functional group is NH2.
Basic Nature of Primary Amines: R-NH3 is an ammonium ion in which an aryl or alkyl group has been substituted for H-atoms. They are proton acceptors therefore they are bronsted lowry bases. With water they form OH(-) ions, so they're weal alkalis. They react with acids to form salts.
Preparation of Amines:
- Straight-Chain (aliphatic) amines: Excess ammonia is refluxed with a halogenoalkane with ethanol as a solvent. RBr + NH3 >>> RNH2 + HBr. Excess ammonia then reacts with the HBr to form ammonium bromide. NH3 + HBr >>> NH4(+)Br(-).
- Aromatic Amines: C6H5NO2 + 6(H) >>> C6H5NH2 + 2H20. Catalyst = Tin and concentrated HCl.