Naming & Drawing Alkanes AS Chemistry Organic Chemistry 1 Naming & Drawing Alkanes
Quiz Write the answers to these questions: The general formula that butane (4 carbons) fits. A molecular formula for methane (1 carbon). A structural formula for ethane (2 carbons) Draw a C-H bond coming out of the page. Draw out the displayed formula for ethene (3 carbons)
Alkanes Objective: to know about alkanes Outcomes: know the general formula for alkanes Know that alkanes and cycloalkanes are saturated hydrocarbons understand the term ‘structural isomerism’ and determine the possible structural, displayed and skeletal formulae of an organic molecule, given its molecular formula be able to name compounds relevant to this specification using the rules of International Union of Pure and Applied Chemistry (IUPAC) nomenclature You will be expected to know prefixes for compounds up to C10
Definitions Hydrocarbon A compound of hydrogen and carbon only. Saturated hydrocarbon A compound containing only single bonds Unsaturated hydrocarbon A compound containing at least one double bond.
More definitions Aliphatic hydrocarbon The carbons are joined together in straight or branched chains. Alicyclic hydrocarbons The carbons are joined together in a ring structure.
Alkanes Draw the Of methane. Now do the same for ethane Propane Butane Molecular formula Structural formula Displayed formula Skeletal formula 3D formula Of methane. Now do the same for ethane Propane Butane
Naming Alkanes The name of simple alkanes is made up of two parts The ending is –ane. The first part shows the number of carbons, e.g. meth- means one carbon Write the names of the alkanes with numbers of carbons from 1 to 10.
Methane, Ethane, Propane, Butane, Pentane, Hexane, Heptane, Octane, Nonane, Decane. Draw the displayed formula and write their molecular formula. What do you notice about their molecular formula? They have the general formula CnH2n+2
Alkanes are saturated hydrocarbons. Why? They only contain single bonds
Cyclohexanes have two fewer hydrogen atoms than straight chained alkanes. They have the general formula CnH2n
Practice Octane is an alkane whose molecules contain 8 carbon atoms. Write the molecular, empirical and structural formulae for octane Draw the displayed and skeletal formula for octane
Alkanes Objective: to know about alkanes Outcomes: know the general formula for alkanes Know that alkanes and cycloalkanes are saturated hydrocarbons understand the term ‘structural isomerism’ and determine the possible structural, displayed and skeletal formulae of an organic molecule, given its molecular formula be able to name compounds relevant to this specification using the rules of International Union of Pure and Applied Chemistry (IUPAC) nomenclature You will be expected to know prefixes for compounds up to C10
Pentane Pentane has the formula C5H12 Draw its displayed formula Can you draw this differently?
Isomerism Most organic compounds share their molecular formula with other compounds. Different compounds sharing the same molecular formula are called isomers Isomers are compounds with the same molecular formula, but different arrangements of atoms in space We saw that pentane, C5H12, can be drawn several different ways.
Definition of Structural Isomerism Structural isomers are molecules with the same molecular formula but with different structural arrangement of atoms. i.e. the same number and type of atoms but joined up in different orders.
Alkanes Objective: to know about alkanes Outcomes: know the general formula for alkanes Know that alkanes and cycloalkanes are saturated hydrocarbons understand the term ‘structural isomerism’ and determine the possible structural, displayed and skeletal formulae of an organic molecule, given its molecular formula be able to name compounds relevant to this specification using the rules of International Union of Pure and Applied Chemistry (IUPAC) nomenclature You will be expected to know prefixes for compounds up to C10
Naming Isomers When we name an organic compound, we start by finding the longest carbon chain through it. This provides the stem of the name, e.g. C H C H H C H H C H H C H butane H
Naming Isomers If the long chain has shorter chains on it, the names of these are prefixed to the name. C H C H H C H H C H H C H methylbutane H
Naming isomers Sometimes we need to add a number to show which atom in the longest chain the extra chain is joined to. We number from the end nearest the group: C H C H H C H 4 3 2 1 H C H H C H 2-methylbutane methylbutane Not necessary!! H
Other rules We include every side-chain in the name, if we have more than one identical side chain we use the prefixes di- (2), tri- (3), etc. If we need to show where the side chains are attached we use numbers e.g.: 2,3,5-trimethylhexane Numbers are separated from each other by commas, from words by hyphens.
Other rules Alkyl groups are placed in alphabetical order e.g.: 3-ethyl-2-methylpentane Compounds containing a ring of carbons are prefixed by cyclo- E.g. cyclohexane
Alkanes Objective: to know about alkanes Outcomes: know the general formula for alkanes Know that alkanes and cycloalkanes are saturated hydrocarbons understand the term ‘structural isomerism’ and determine the possible structural, displayed and skeletal formulae of an organic molecule, given its molecular formula be able to name compounds relevant to this specification using the rules of International Union of Pure and Applied Chemistry (IUPAC) nomenclature You will be expected to know prefixes for compounds up to C10
Practice Heptane is an alkane with the molecular formula C7H16 Practice Heptane is an alkane with the molecular formula C7H16. Draw as many isomers for it that you can think of and name them.
Practice OCR book page 104 - 113
Make a challenge In your group, invent 3 compounds. Draw the displayed formulae On a separate sheet, write the names of them. Another group will try to name your compounds.
Alkanes Objective: to know about alkanes Outcomes: know the general formula for alkanes Know that alkanes and cycloalkanes are saturated hydrocarbons understand the term ‘structural isomerism’ and determine the possible structural, displayed and skeletal formulae of an organic molecule, given its molecular formula be able to name compounds relevant to this specification using the rules of International Union of Pure and Applied Chemistry (IUPAC) nomenclature You will be expected to know prefixes for compounds up to C10