IUPAC naming and formulae
Download as DOCX, PDF1 like3,254 views
The document explains the IUPAC naming system for organic compounds, detailing the rules for naming based on functional groups, carbon chain length, and branching. It outlines key steps including identifying functional groups, determining the longest carbon chain, and naming branched groups, along with the appropriate suffixes and prefixes. Examples illustrate the application of these rules for naming hydrocarbons and alkanes.
More Related Content
Similar to IUPAC naming and formulae (20)
More from Microbiology (20)
IUPAC naming and formulae
- 1. 1 IUPAC Naming and Formulae What is IUPAC naming? In order to give compounds a name, certain rules must be followed. When naming organic compounds, the IUPAC (International Union of Pure and Applied Chemistry) nomenclature (naming scheme) is used. This is to give consistency to the names. It also enables every compound to have a unique name, which is not possible with the common names used (for example in industry). We will first look at some of the steps that need to be followed when naming a compound, and then try to apply these rules to some specific examples. A good general rule to follow is to start at the end (the suffix) and work backwards (from right to left) in the name. Molecules can contain both double or triple bonds and other functional groups (e.g. an alkene and an alcohol functional group in one molecule - propenol). However, all molecules explored in this book will contain only single carbon-carbon bonds when combined with other functional groups. 1. Recognize the functional group in the compound. This will determine the suffix of the name. Functional group suffix alkane -ane alkene -ene alkyne -yne alcohol -ol aldehyde -al ketone -one carboxylic acid -oic acid ester -oate The suffix associated with various functional groups.
- 2. 2 Find the longest continuous carbon chain that contains the functional group (it won't always be a straight chain) and count the number of carbon atoms in this chain. This number will determine the prefix (the beginning) of the compound's name Carbon atoms Prefix 1 meth- 2 eth- 3 prop- 4 but- 5 pent- 6 hex- 7 hept- 8 oct- 9 non- 10 dec- Table 4.6: The prefix of a compound's name is determined by the number of carbon atoms in the longest chain that contains the functional group. 2. Number the carbons in the longest carbon chain (Important: If the molecule is not an alkane (i.e. has a functional group) you need to start numbering so that the functional group is on the carbon with the lowest possible number). Start with the carbon at the end closest to the functional group. 3. Look for any branched groups: Name them by counting the number of carbon atoms in the branched group and these groups will all end in -yl. Note the position of the group on the main carbon chain. If there is more than one of the same type of branched group then both numbers must be listed (e.g. 2,4 -) and one of the prefixes listed in must be used. Important: If the molecule is an alkane the branched group must be on the carbon with the lowest possible number. The branched groups must be listed before the name of the main chain in alphabetical order (ignoring di/tri/tetra). If there are no branched groups this step can be ignored.
- 3. 3 Number prefix 2 di- 3 tri- 4 tetra- Prefixes for multiple substituents with the same name. These apply to multiple functional groups as well. 4. For the alkyl halides the halogen atom is treated in much the same way as branched groups: To name them take the name of the halogen atom (e.g. iodine) and replace the - ine with -o (e.g. iodo). Halogen name fluorine fluoro chlorine chloro bromine bromo iodine iodo Naming halogen atoms in organic molecules. Give the halogen atom a number to show its position on the carbon chain. If there is more than one halogen atom the numbers should be listed and a prefix should be used (e.g. 3,4-diiodo- or 1,2,2-trichloro-). The halogen atoms must be listed before the name of the main chain in alphabetical order (ignore di/tri/tetra). If there are no halogen atoms this step can be ignored. 5. Combine the elements of the name into a single word in the following order: branched groups/halogen atoms in alphabetical order (ignoring prefixes) prefix of main chain name ending according to the functional group and its position on the longest carbon chain.
- 4. 4 Naming hydrocarbons Naming alkanes The suffix for an alkane is -ane. WORKED EXAMPLE 1: NAMING THE ALKANES Give the IUPAC name for the following compound: Note: The numbers attached to the carbon atoms would not normally be shown. The carbon atoms have been numbered to help you to name the compound. Identify the functional group The compound is a hydrocarbon with single bonds between the carbon atoms. It is an alkane and will have a suffix of -ane. Find the longest carbon chain There are four carbon atoms in the longest chain. The prefix of the compound will be but-. Number the carbon atoms in the longest chain The numbering has been done for you here. Look for any branched group, name them and give their position on the carbon chain There are no branched groups in this compound.
- 5. 5 Combine the elements of the name into a single word The name of the compound is butane. WORKED EXAMPLE 2: NAMING THE ALKANES Give the IUPAC name for the following compound: Identify the functional group The compound is a hydrocarbon with single bonds between the carbon atoms. It is an alkane and will have the suffix -ane. Find the longest carbon chain There are three carbon atoms in the longest chain. The prefix for this compound is prop-. Number the carbons in the carbon chain If we start at the carbon on the left, we can number the atoms as shown in red (left). If we start at the carbon on the right, we can number the atoms as shown in blue (right).
- 6. 6 Look for any branched groups, name them and give their position on the carbon chain There is a branched group attached to the second carbon atom. In this case the methyl group is on carbon 2 regardless of which side you number the longest chain from. This group has the formula (text{CH}_{3}), which is methane without a hydrogen atom. However, because it is not part of the main chain, it is given the suffix -yl (i.e. methyl). The position of the methyl group comes just before its name (see the next step). Combine the elements of the compound's name into a single word in the order of branched group; prefix; name ending according to the functional group The compound's name is 2-methylpropane.