Starter: Structures Draw full displayed formulas and skeletal structures for: Propane Butane Pentane Hexane Heptane

Skeletal Structures

REPRESENTING MOLECULAR STRUCTURES: Summary Three different formats may be used: 1. DISPLAYED FORMULAS these show ALL atoms and ALL bonds 2. STRUCTURAL FORMULAS these ABBREVIATE displayed formulas to a single line representation 3. SKELETAL FORMULAS these ABBREVIATE displayed formulas by OMITTING H ATOMS and representing C TO C BONDS AS STRAIGHT LINES such that the points where lines meet or the ends of lines represent the C atoms H C O 1. OH 3. CH3C(CH3)(OH)CH3 2. All represent 2-methylpropan-2-ol

What do you think this compound is called? What is the structural formula for the following compound? What do you think this compound is called? Optional Extra

Functional Group Most organic compounds made up of a hydrocarbon chain that has one or more reactive groups attached to it. FUNCTIONAL GROUPS The functional group reacts the same way, whatever the length of the hydrocarbon chain. “An atom or group of atoms in an organic molecule that is responsible for the characteristic reactions of that molecule” Ask pupils if any ideas or examples of functional groups.

IUPAC The system we use for naming compounds was developed by the International Union of Pure and Applied Chemistry or IUPAC. This means that chemists throughout the world use the same conventions, rather like a universal language of chemistry. Systematic names tells us about the structures of the compounds rather than just the formula.

Nomenclature Rules The name is based around the name of the longest carbon chain (which contains the functional group).

Roots A systematic name has a root that tells us the longest unbranched hydrocarbon chain or ring. The first six roots used in naming organic compounds: Number of Carbons Root 1 Meth- 2 3 4 5 6

Roots A systematic name has a root that tells us the longest unbranched hydrocarbon chain or ring. The first six roots used in naming organic compounds: Number of Carbons Root 1 Meth- 2 Eth- 3 Prop- 4 But- 5 Pent- 6 Hex-

Nomenclature rules 2. The functional group is indicated by a prefix or suffix. Prefixes and suffixes describe the changes that have been made to the root molecule. Prefixes are added to the beginning of the root. Suffixes are added to the end of the root.

Ethane The syllable after the root tells us whether there are any double bonds. - ane means no double bonds.

- ene means there is a double bond. Ethene The syllable after the root tells us whether there are any double bonds. - ene means there is a double bond. EXTENSION: Ethyne – shown in last lesson. Don’t need to know name at AS Level.

What do you think “R” and “X” mean? Family Formula Suffix Example Alkanes   R-H -ane Ethane Alkenes R-CH=CH2 -ene Propene Haloalkanes R-X None Chloromethane Alcohols R-OH -ol Ethanol Aldehydes R-CHO -al Ethanal Ketones R-COR’ -one Propanone Carboxylic Acids R-COOH -oic acid Ethanoic Acid EXT: What do you think “R” and “X” mean? For the moment they only need to be bale to name ALKANES, ALKENES and HALOALKANES EXT: What do R and X mean?

What is the “R” for? R is often used to represent a hydrocarbon chain (of any length). Think of it as representing the rest of the molecule.

Halogens Halogenoalkanes: “halo-” prefix Fluorine - Fluoro Chlorine - Chloro Bromine - Bromo Iodine – Iodo We usually use an “X” instead of an “R” to represent a halogen in a general formula.

Homologous Series “A series of chemically similar compounds which conform to a general formula. Each member of the series differs from the next by CH2 And the members of the series show a graduation in physical properties.” Based on new knowledge of functional groups, ask pupils to figure out what an homolougous series is. Each one differs from the next by CH2: Ask pupils to prove this by looking at alkanes, alkenes, alcohols etc.

Prefixes Questions: 1. What do you think C2H5OH is called? Side chains are shown by a prefix, whose name tells us the number of carbons. Methyl = CH3- Ethyl = C2H5- Propyl = C3H7- Butyl = C4H9 - Questions: 1. What do you think C2H5OH is called? 2. What do you think the molecular formula is for “hexyl” prefix?

Prefixes: e.g, Methylbutane The longest unbranched chain is four carbons long, which gives us butane (as there are no double bonds). There is a side chain of one carbon, a methyl group. Methylbutane

Suffixes: e.g., The longest unbranched chain is one carbon long, which gives us methan- This is an alcohol as it has an -OH group so has a suffix of “ol” Methanol

Task: Name the following Bromomethane, propene and methanol

Nomenclature Rules 3. The position of the functional group is given by a number – counting from the end that gives the functional group the lowest number. NB: We only include numbers if they are needed.

E.g., Methylpentane Ask pupils to draw and hold up. Hopefully get a mixture of 2- and 3-methyl pentane. Discuss numbering the carbonatoms to show us the position and branching in a chain and the position of a functional group.

We ALWAYS use the smallest possible number E.g., 1-Bromopropane Ask pupils to draw and hold up. Highlight the fact that they are ALL 1-Bromopropane. We ALWAYS use the smallest possible number.

Nomenclature Rules 4. Where there are two or more of the same groups, di-, tri- or –tetra are used. What would you use if there were 6 of the same group? If there is more than one functional group/subsitutent, numbers are separated by commas and the groups are listed in alphabetical order (ignoring di, tri, etc.). 3-bromo-1-chlorobutane 2,2-dibromo-1-chlorobutane.

Nomenclature Rules 5. The suffix for alkenes can go in front of other suffixes. e.g. 2-chlorobut-3-enal.

Finisher Starter for 10 5.1.2 Nomenclature EXT: Create you own molecule and name it! RSC Starter for 10 5.1.2 Nomenclature