Organic Chemistry Introduction PDF

11.1 Formulae, functional groups and terminology Draw and interpret the displayed formula of a molecule to show all the atoms and all the bonds The displayed formula shows all the atoms of each element and all the bonds in the molecule E.g. The molecular formula of methane is CH4...

11.1 Formulae, functional groups and terminology Draw and interpret the displayed formula of a molecule to show all the atoms and all the bonds The displayed formula shows all the atoms of each element and all the bonds in the molecule E.g. The molecular formula of methane is CH4, draw the displayed formula of methane. ○ We know that each hydrogen atom can only form 1 bond whereas a carbon atom can form 4 bonds so the displayed formula of CH4 would be: E.g. The molecular formula for ethanoic acid is CH3COOH, draw the displayed formula of ethanoic acid. ○ We know that each hydrogen atom can only form 1 bond, a carbon atom can form 4 bonds and an oxygen atom can form 2 bonds so the displayed formula of CH3COOH would be: Write and interpret general formulae of compounds in the same homologous series, limited to: The general formula is a formula followed by all the compounds in the same homologous series representing the composition of the atoms present in each molecule (a) Alkanes, CnH2n+2 The general formula for an alkane is CnH2n+2 E.g. An alkane has 5 carbon atoms, what is the molecular formula of this alkane? ○ 5 carbon atoms means n is 5 so working out no. of H atoms: 2(5) + 2 = 12 ○ The molecular formula is C5H12 (pentane) (b) Alkenes, CnH2n The general formula for an alkene is CnH2n E.g. An alkene has 4 carbon atoms, what is the molecular formula of this alkene? ○ 4 carbon atoms means n is 4 so working out no. of H atoms = 2(4) = 8 ○ The molecular formula is C4H8 (butene) (c) Alcohols, CnH2n+1OH The general formula for an alcohol is CnH2n+1OH E.g. An alcohol has 4 carbon atoms, what is the molecular formula of this alcohol? ○ 4 carbon atoms means n is 4 so working out no. of H atoms = 2(4) + 1 =9 ○ The molecular formula is C4H9OH (butanol) (d) Carboxylic acids, CnH2n+1COOH The general formula for a carboxylic acid is CnH2n+1COOH E.g. A carboxylic acid has a total of 4 carbon atoms, what is the formula of this carboxylic acid? ○ 4 carbon atoms including the functional group COOH, so n is 3 so working out no. of H atoms = 2(3) + 1 = 7 ○ The formula is C3H7COOH (butanoic acid) Identify a functional group as… The functional group is an atom or group of atoms that determine the chemical properties of a homologous series E.g. The functional group of an alcohol is the hydroxyl group (-OH) State that a homologous series is… A homologous series is a family or group of similar compounds with similar chemical properties due to the presence of the same functional group State that a saturated compound… A saturated compound has molecules in which all carbon-carbon bonds are single bonds E.g. All alkanes are saturated compounds since they only have single carbon-carbon bonds. State that an unsaturated compound… An unsaturated compound has molecules in which one or more carbon-carbon bonds are not single bonds E.g. Alkenes are unsaturated since they all have at least one double carbon-carbon bond. (Extended only) State that a structural formula is an unambiguous description of the way the atoms in a molecule are arranged, including CH2=CH2, CH3CH2OH, CH3COOCH3 The structural formula is a formula which shows the arrangement of atoms in the molecule of a compound but does not show all the bonds between them. E.g. CH2=CH2 is the structural formula for ethene (molecular formula C2H4) and shows where the double bond lies E.g. CH3CH2OH is the structural formula for ethanol (molecular formula C2H5OH) E.g. CH3COOCH3 is the structural formula for methyl ethanoate (an ester with the molecular formula C3H6O2) (Extended only) Define structural isomers as compounds with the same molecular formula, but different structural formulae, including C4H10 as CH3CH2CH2CH3 and CH3CH(CH3)CH3 and C4H8 as CH3CH2CH=CH2 and CH3CH=CHCH3 Structural isomers are compounds with the same molecular formula but different structural formula  E.g. C4H10 has 2 structural isomers: ○ The structural isomers of C4H10 differ in that 2-methylpropane has a side group (a methyl group) whereas butane is a straight chain molecule E.g. C4H8 has 2 structural isomers: ○ The structural isomers of C4H8 differ in where the double bond lies in the structure  (Extended only) Describe the general characteristics of a homologous series as… The general characteristics of a homologous series are: ○ have the same functional group ○ have the same general formula ○ differ from one member to the next by a –CH2– unit ○ display a trend in physical properties ○ share similar chemical properties 11.2 Naming organic compounds Name and draw the displayed formulae of: (a) Methane and Ethane Methane (CH4) and ethane (C2H6) are both alkanes. (b) Ethene Ethene is an alkene with 2 carbon atoms (the molecular formula C2H4) and a double bond between the carbon atoms.  (c) Ethanol Ethanol is an alcohol with molecular formula C2H5OH so has a hydroxyl group (-OH) attached to one of the carbon atoms (d) Ethanoic acid Ethanoic acid is a carboxylic acid with structural formula CH3COOH so has a carboxyl group (-COOH) in its structure (e) The products of the reactions stated in sections 11.4–11.7 See notes 11.4-11.7  State the type of compound present, given a chemical name ending in -ane, -ene, -ol, or -oic acid or from a molecular formula or displayed formula Type of Chemical name General Example Example (displayed compound ending in formula (molecular formula) formula) Alkane -ane CnH2n+2 CH4 Alkene -ene CnH2n C2H4 Alcohol -ol CnH2n+1OH C2H5OH Carboxylic -oic acid CnH2n+1COOH CH3COOH acid (Extended only) Name and draw the structural and displayed formulae of unbranched: (a) Alkanes Naming alkanes is relatively easy as all the names end in -ane To know the prefix, count the number of carbon atoms:  Number of carbons Prefix Name of alkane 1 meth- methane 2 eth- ethane 3 prop- propane 4 but- butane 5 pent- pentane 6 hex- hexane 7 hept- heptane 8 oct- octane To draw the displayed formula of alkanes, remember: ○ There are only single carbon-carbon bonds ○ Carbon atoms must have 4 bonds ○ Hydrogen atoms must have 1 bond ○ If there are side groups, e.g. a methyl group, attach it to the correct carbon as numbered in the name of the alkane (b) Alkenes, including but-1-ene and but-2-ene Naming alkenes is relatively easy as all the names end in -ene But numbers are included in the name between the prefix (number of carbon atoms) and the suffix -ene, to show which carbon atom the double carbon-carbon bond is attached to E.g. But-1-ene has the double carbon=carbon bond on carbon-1 whereas but-2-ene has the double carbon=carbon bond on carbon-2: (c) Alcohols, including propan-1-ol, propan-2-ol, butan-1-ol and butan-2-ol All the names of alcohols end in -ol But numbers are included in the name between the prefix (number of carbon atoms) and the suffix -ol, to show which carbon the hydroxyl (-OH) group is attached to E.g. Propan-1-ol has the hydroxyl group on carbon-1 whereas propan-2-ol has the hydroxyl group on carbon-2: E.g. Butan-1-ol has the hydroxyl group on carbon-1 whereas butan-2-ol has the hydroxyl group on carbon-2: (d) Carboxylic acids containing up to four carbon atoms per molecule All the names of carboxylic acids end in -oic acid The carboxyl group (-COOH) is always at the end of the carbon chain so there is no need to number where it goes (Extended only) Name and draw the displayed formulae of the unbranched esters which can be made from unbranched alcohols and carboxylic acids, each containing up to four carbon atoms Unbranched esters are formed from unbranched alcohols and carboxylic acids The functional group of esters is -COO which is known as an ester linkage/bond To name an ester: 1. Change the name of the alcohol to end in –yl 2. Change the name of the carboxylic acid to end in –oate 3. Alcohol name goes to the front, carboxylic acid name to the back E.g. Methyl ethanoate is formed from methanol and ethanoic acid:  11.3 Fuels Name the fossil fuels The fossil fuels are coal, natural gas and petroleum (crude oil). Name the main constituent of natural gas… The main constituent of natural gas is methane, CH4. State that hydrocarbons are… Hydrocarbons are compounds that only contain hydrogen and carbon. E.g. alkanes are hydrocarbons. State that petroleum is a mixture of hydrocarbons Petroleum is a mixture of hydrocarbons Crude oil is another term used interchangeably with petroleum, crude oil is the raw form of petroleum before it is refined and processed. Petroleum is a finite resource found in rocks and formed from the remains of an ancient biomass consisting mainly of plankton that was buried in mud. Describe the separation of petroleum into useful fractions by fractional distillation Petroleum can be separated into its constituent fractions by a separating process known as fractional distillation Fractional distillation separates compounds into its constituent substances based on their differences in boiling points Crude oil is heated in a furnace until it is vaporised and is added to a fractionating column, that has divisions at different levels to collect the various constituents (fractions) Fractions will separate into its constituent levels based on their properties: different boiling points, chain length, volatility and viscosity. Typical fractions collected include: ○ Refinery gases (e.g., propane, butane) at the top. ○ Gasoline (petrol) slightly lower. ○ Kerosene (jet fuel) mid-level. ○ Diesel below kerosene. ○ Heavy fuel oil near the bottom. ○ Residue (e.g., bitumen) at the very bottom. Describe how the properties of fractions obtained from petroleum change from the bottom to the top of the fractionating column, limited to: (a) Decreasing chain length Fractions with shorter carbon chains, such as propane, will be tapped from the top of the fractionating column. Fractions with longer chain lengths will collect at the bottom of the fractionating column. (b) Higher volatility Fractions with higher volatility will separate off at the top of the fractionating column Fractions with lower volatility will collect at the bottom of the fractionating column (c) Lower boiling points Fractions with lower boiling points condense at higher levels (top of the column). Fractions with higher boiling points condense at lower levels (bottom of the column). (d) Lower viscosity Viscosity refers to how thick and sticky and substance is Hydrocarbons with lower viscosity, such as refinery gases, will separate off at the top of the column Hydrocarbons with higher viscosity, such as bitumen will collect at the bottom of the fractionating column Name the uses of the fractions as: Petroleum is separated into fractions since its individual constituents have various utility functions such as: (a) Refinery gas fraction Gas used in heating and cooking (b) Gasoline /petrol fraction Fuel used in cars (c) Naphtha fraction Used as a chemical feedstock (d) Kerosene /paraffin fraction Used for jet fuel (e) Diesel oil/ gas oil fraction Fuel used in diesel engines (f) Fuel oil fraction Fuel used in ships Fuel for home heating systems (g) Lubricating oil fraction Used for lubricants, waxes and polishes (h) Bitumen fraction Used for making roads