2Hydrocarbons A molecule containing only carbon and hydrogen atoms. When we look at molecules, BLACK always means CARBON, and WHITE (and sometimes grey) means HYDROGEN.Hydrocarbons are the simplest organic molecules
3Alkanes CnH2n+2 Alkanes are a family of hydrocarbons All single bonds – carbon is bonded to four other atomsAlkanes are aliphatic – they form chains and non-aromatic rings (we’ll learn about aromatic molecules later)Alkanes, like other hydrocarbon chains, form a homologous seriesThis means that adding a single carbon to the chain increases the number of hydrogens by a definite numberIn the case of alkanes, # hydrogens = (2 x # carbons) + 2CnH2n+2
4Fractional Distillation Boiling points of alkanes increase with size, so refineries can use this property to separate crude oil into its componentsComponents:< 20oC: Small gaseous alkanes, usually further refined or liquefied20-100oC: Slightly larger, used as solvents or further refinementUp to 200oC: Straight-run gasoline – this gets refined and sold as common fuelUp to 300oC: Large alkanes, used for kerosene and jet fuelUp to 400oC: Larger alkanes, used as oil and diesel fuelRemaining unboiled liquids are used as lubricating oilsSolid residues are used for asphalt, tar, and paraffin wax.
5Uses of Alkanes Methane (natural gas) Butane lighters Automotive and industrial lubricantsVaseline (also a lubricant)Commercial Gasoline (petrol)Other Fuels (propane tanks)Tar (used in asphalt)Candle wax
6How do we name them?So, how did we come to call them methane, propane, butane, octane…?IUPAC (International Union of Pure and Applied Chemistry) devised a system to name organic moleculesIt uses a set of suffixes and prefixes to identify all organic molecules, from the simplest to the ridiculously complexIt can get quite complex for very large molecules, which is why many compounds still use common names
7The Name Think of naming a molecule as just like naming a person: First Name(1) + Middle Names(2) + Family Name(3)Molecule:Branch Prefixes(2) + Root Name (1) + Family Suffixes(3)Alkanes all have the family suffix –ane.
8IUPAC NomenclatureThere are lots of rules, but we’re going to learn them as we go.When identifying a hydrocarbon, first find the longest chain of carbons that are bonded to each other (no breaks in the chain)The longest chain ISN’T always the one going straight across!38
9Root NameThe longest carbon chain is known as the parent chain. The root name tells you how many carbons are in the parent chain.Each prefix below refers to a number of carbons:# of CarbonsPrefix1Meth-2Eth-3Prop-4But-5Pent-6Hex-7Hept-8Oct-
10MethaneEthanePropaneThe First Six AlkanesButaneHexanePentane
11Practice makes Perfect! You need to practice naming lots of molecules!Complete Alkane WorksheetIf you have any questions, make sure you ask me!Do the following questions: (for homework)P. 330 (#1, 2, 4) and p. 332 (all 4)