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CHEM 131 How to name organic hydrocarbons – A quick tutorial Prefix Root The position & type of functional groups The longest chain Ending Class of compound Always be systematic and do all the steps in order until you are comfortable with naming compounds. Skipping steps while you are learning how to name molecules can make it more confusing than it needs to be. # of C’s 1 2 3 4 5 6 7 8 9 10 As “Longest Chain” Condensed Formula Alkane Root Name CH4 methane CH3-CH3 ethane CH3-CH2-CH3 propane CH3-CH2-CH2-CH3 butane CH3-CH2-CH2-CH2-CH3 pentane CH3-(CH2)4-CH3 hexane CH3-(CH2)5-CH3 heptane CH3-(CH2)6-CH3 octane CH3-(CH2)7-CH3 novane CH3-(CH2)8-CH3 decane As “Functional Group” Condensed Formula Alkyl Name -CH4 -CH2-CH3 -CH2-CH2-CH3 -CH2-CH2-CH2-CH3 -CH2-CH2-CH2-CH2-CH3 -(CH2)5-CH3 -(CH2)6-CH3 -(CH2)7-CH3 -(CH2)8-CH3 -(CH2)9-CH3 methyl ethyl propyl butyl pentyl hexyl heptyl octyl novyl decyl Step 1: Identify the longest chain (root name) Remember the longest chain is not necessarily straight across (it can be drawn with a few bends in the chain) Cyclopentane For cycloalkanes, the longest chain is the ring For alkenes or alkynes, the double or triple bond has to be part of the chain Write down the base name. For example: nonane Step 2: Number the longest chain Find the combination that will give the lowest set of numbers for all branches or functional groups. For alkanes you are looking for the overall lowest set of numbers. For all other functional groups you want the lowest number possible for the functional group, ie the alkene and the alkyne number should be as low as possible. Maxi Boeckl 4/20/10 CHEM 131 nonane 1 5 5 6 7 8 9 4 1 2 1 2 3 3 2 Cyclopentane 6 4 5 3 4 1-hexene Step 3: Identify the location of the functional groups and identify them When naming the functional group, do not count any of the carbons that were already included in the longest chain. Write down the # (location) – with the functional group next to it. Looking at example 1: nonane o 2-methyl 7 9 8 6 5 o 4-butyl o 6-methyl 1 2 3 4 Example 2: o 1-butyl (do not count the C that is part of the ring – you already accounted for that one by including that in cyclopentane) o 2-methyl Example 3: o 1 ene (double and triple bonds are considered functional groups) o 2-methyl o 3-ethyl o Two 4-methyl groups 1' C 2' 4' 3' Cyclopentane 1 2 3 6 4 5 1-hexene At this point if you have more than one of the same groups, start grouping them together. Remember to use the prefixes di-, tri-, tetra- etc. Remember that alkenes are also functional groups and you would name multiple double bonds -diene and -triene, etc. o For example 1, this would give : 2,6-dimethyl o For example 2, this would give: 2,4,4-trimethyl Step 4: Put all the different part together Before putting the functional groups in front of the root name, alphabetize the functional groups. Remember to ignore the prefix di-, tri-, tetra- etc. The three examples are: o 4-butyl-2,6-dimethylnonane o 1-butyl-2-methylcyclopentane o 3-ethyl-2,4,4-trimethyl-1-hexene Some more examples: You will start numbering from the left (end closest to triple bond). As with alkenes, the C-C triple bond has to be part of the longest chain. There are 6 carbons with the triple bond at position 2 and a methyl at position 4. Name: 4-methyl-2-hexyne C C In this example you have a benzene ring with two branches, 2 ethyl groups at positions 1 and 3. Since this benzene ring is not one of the common base groups used with benzene rings, the name would be 1,3-diethylbenzene. Maxi Boeckl 4/20/10 CHEM 131 OH Compare this to the following, where we have phenol (shown in red) as the base name with an additional ethyl group. Thus 3-ethylphenol. Review your aromatic base names! Finally, last example: Again we have 5 carbons in the longest chain, with the double bond being at position 2. Remember, you number so that the double bond has the lowest number. This would put the methyl in position 4. The double bond is trans, so we need to include that in the name. Name: 4-methyl-trans-2-pentene Maxi Boeckl 4/20/10