Naming Branched Alkanes Grade 11 Chemistry Shelley MacGibbon

INDEX Substituents Naming Branched Alkanes Finding the Longest Chain Numbering the Carbons Identifying the Branches Rules of Nomenclature Naming Our Molecule More Complex Example

Alkanes Alkanes have all single bonds. They can either be in a ‘straight chain’ or they can have one or more substituents. Straight Chain Molecule INDEX

Substituents Substituents are any functional group which is not part of the main chain. They look like branches. Substituent of the main chain. INDEX

Naming Branched Alkanes 1.Find the longest continuous chain of carbons in the molecule. 2.Number the carbons in the main chain ONLY! Start closest to the first branching point. 3.Identify all branches and assign each a number. 4.Name the molecule using the rules of nomenclature. INDEX

Finding the Longest Chain It must be continuous. This means that you cannot backtrack or lift your pencil from the paper. Longest chain INDEX

Numbering the Carbons Number only those carbons in the main chain. Remember to start at the carbon closest to the first branch point. YESNO INDEX

Identifying the Branches Identify all branches on the main chain, name them, and assign them a number according to what carbon they are attached to meth- group on Carbon #2 eth- group on Carbon #4 INDEX

Rules of Nomenclature All substituents’ names end in –yl Ex: methyl The number of the carbon the substituent is attached to goes in front of the substituent name and is separated with a hyphen (-) Ex: 2-methyl If there is more than one substituent, they are separated by a hyphen. Ex: 2-methyl-3-ethyl When there is more than one substituent with the same name the numbers of each of the carbons they are attached to are separated by commas(,). A prefix which tells you how many of that substituent there are must also be used. Ex: 2,4-dimethyl Cont’d

Rules of Nomenclature (cont’d) When naming the molecule, always start with the lowest number. Ex: 2-methyl-5- propyl. After all branches have been named, the very last substituent is written directly before the name of the main chain. Ex: 2-methyl-3-ethyldecane INDEX

Naming Our Molecule Methyl on carbon #2 Ethyl on carbon #4 Main chain has 6 carbons  hexane Name: 2-methyl-4-ethylhexane INDEX

More Complex Example CH Name: 3,5-dimethyl-5-propyl-7-ethyldecane INDEX