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4.1 Systematic Nomenclature 1 Definitions Molecular formula Number of atoms in a molecule (element or compound) e.g. C2H4O2 Empirical formula Simplest whole number ratio of atoms in a compound e.g. CH2O Structural formula Shows the shape and arrangement of atoms in a compound e.g. CH3COOH 2 Definitions Structural isomers Same molecular formula but different structural formula e.g. C2H4O2 O O H H H C H C C C H Ethanoic Acid H H O O H Methyl methanoate 3 Definitions Homologous Series Conform to a general formula Have the same functional group Similar chemical properties Physical properties gradually change 4 Definitions Saturated compounds No multiple bonds between carbon atoms Unsaturated compounds At least one C=C or C≡C bond Aromatic compound Contains a benzene ring R 5 Systematic Nomenclature Organic compounds Consist of: Hydrocarbon chain or ring which is non polar and usually unreactive (when saturated) Functional group/s which are involved in chemical reactions and affect physical properties of the compound 6 Naming Organic Compounds Find the longest chain of carbons. If there is a functional group it must be attached to one of these carbons. No. of carbon atoms Prefix 1 2 3 4 5 6 7 8 Meth Eth Prop But Pent Hex Hept Oct 7 Naming Organic Compounds Identify side chains off the main carbon chain. Naming includes number and type of side chains and their position along the main chain. No. of branches of same type 2 3 4 Prefix Di Tri Tetra Name Methyl Ethyl Propyl Butyl Alkyl CH3group C3 H 7 - C4 H 9 - C2 H 5 - 8 Naming Organic Compounds Identify the Functional Group Homologous Suffix series H Alkane -ane H Alkene -ene Alkyne -yne Alcohol Aldehyde -ol -al H C C H H C C H H H C O H H O H H C H C H 9 Naming Organic Compounds O H Homologous Suffix series Ketone Carboxylic acid H C Carboxylate -oate ion ion H H C H -one -oic acid C H O H H C C H H O O H H C H – C O 10 Naming Organic Compounds Homologous Suffix Series H H Amine -amine Amide -amide O H H C H H N H H C N H H H H O H C H C N H H C H C H C H N H H H C H H 11 Name the following systematically: H H H H H H H H C H H C C C C C C C H H H H H O H H H H H C H H H H H H H C C C C C C C C Br Br H H H C C H H C H H C H H H H H H H H C H H C H H H C H H C H H H 12 4.2 Physical Properties 13 Physical Properties Melting point tm Boiling point tb Solubility in water These properties are affected by the length of the carbon chain and the functional group. 14 Carbon Chains C–C bond is non polar C–H bond is virtually non polar Tetrahedral symmetry around each carbon results in carbon chains being non polar. Polarity of a carbon compound is determined by the polarity of the functional group/s 15 Alkanes Alkane Tb oC CH4 C2H6 C3H8 C4H10 C5H12 -162 -89 -42 -0.5 36 •Non polar molecules •Secondary forces are Dispersion forces •Low tm/tb •As chain length increases (molar mass increases). Dispersion forces increase. 16 Aldehydes Aldehyde Tb oC CH2O C2H4O C3H6O C4H8O C5H10O -19 20 48 75 103 •Polar functional group R H C •Secondary forces are dipoledipole interactions O •tm/tb higher than corresponding alkane 17 Aldehydes Effect of the functional group on tb decreases as the carbon chain length increases Alkane -162 -89 -42 -0.5 Aldehyde -19 20 Difference 143 109 90 48 75 75.5 18 Alcohols Alcohol CH3OH C2H4OH C3H7OH C4H9OH C5H11OH Tb oC 65 H R C O H H 78 97 118 138 •Polar functional group •Secondary forces are Hydrogen bonds •tm/tb are higher than the corresponding alkane or aldehyde 19 Alcohols Effect of the functional group on tb decreases as the carbon chain length increases Alkane -162 -89 -42 -0.5 Alcohol 65 Difference 227 167 139 118.5 78 97 118 20 Carboxylic acids Acid CH2O2 C2H4O2 C3H6O2 C4H8O2 C5H10O2 Tb oC O 101 141 163 186 R •Very polar functional group C •Secondary forces are Hydrogen bonds O H 118 •tm/tb are higher than the corresponding alkane or aldehyde or alcohol 21 Other Polar Functional Groups H R C H •Amines: Hydrogen bonds H •Ketones and Esters: Dipole-dipole interactions N H O R R C C R O O R 22 Effect of functional group on Tb H H H C C H C H C O H C H O •Propanoic acid: 141oC C C O •Methyl ethanoate: 57oC H H H C H C O H H O H H O H •Ethyl methanoate: 55oC H H 23 Solubility “Like dissolves like” To determine the solubility of organic compounds consider: The number and types of functional groups (Identify the secondary bonding) The size/ length of the non polar carbon chain 24 Solubility in water To be soluble in water an organic compound must Hydrogen bond with the water. As the carbon chain increases the solubility decreases 25 4.3 Alcohols 26 Alcohols Ethanol production 80% from fermentation of glucose C6H12O6 which is a monosaccharide. The glucose is obtained directly from fruits (e.g. grapes) or from the hydrolysis of disaccharides or polysaccharides (starch) from vegetables and grains. 27 Hydrolysis (C6H10O5)n +½nH2O ½nC12H22O11 polysaccharide disaccharide C12H22O11 + H2O 2C6H12O6 disaccharide monosaccharide Overall (C6H10O5)n +nH2O nC6H12O6 28 Ethanol production C6H12O6 2C2H5OH +CO2 H=ve Conditions Presence of yeast Temperature of 20-30oC which is maintained so the enzymes in the yeast catalyse the reaction. Almost complete absence of oxygen. Small amount required for yeast metabolism but too much will oxidise the alcohol 29 Alcohols •Primary alcohol H R C O H H R H C H •Secondary alcohol O O H R R •Tertiary alcohol C R R 30 Oxidation of Alcohols Primary and secondary alcohols can be oxidised by an oxidising agent like acidified dichromate Cr2O72– Cr3+ orange green Tertiary alcohols are NOT oxidised by dichromate ions. This reaction and the products formed can be used to identify the type of alcohol present 31 Oxidation of Alcohols Primary alcohols Oxidised to the corresponding aldehyde and then carboxylic acid H H C H H C H O H O H H C H C H O H C C H H O H 32 Oxidation of Alcohols Secondary alcohols Oxidised to the corresponding ketone H H H H C C C H H O H H O H H C C H H C H H 33 34