23: Naming Organic Compounds

Naming Organic Compounds/IUPAC Nomenclature:

Alkyl Group: a functional group attached to another hydrocarbon that contains only carbon and hydrogen atoms. Here, we'll only deal with the first two, methyl and ethyl.

Methyl: –CH₃



The blue shading is the main chain of carbons and the pink shading is methyl group. On a skeletal structure, it looks like one extra line protruding from the main chain, to show another carbon to carbon link with the three hydrogens implied on its end. Here is an example of a main chain with the structure of hexane with a methyl group attached to it:



Ethyl: –C₂H₅



Again, the blue is the main chain and the pink is the ethyl group. On a skeletal structure, it looks like an extra line with a kink in it protruding from the main chain. Here is an example of a main chain with the structure of heptane with an ethyl group attached to it:





(Rules for naming taken off of the handout from class)

Naming Alkanes:

1. Find parent chain: longest continuous chain of carbons. It will not always be straight across. In some of the examples, what appears to be an ethyl group is actually the end of the parent chain. The parent chain is named according to how many carbons it has: butane if it has four carbons, pentane if it has five carbons, etc. This will go at the very end of the name when we're done.

2. Find and identify the alkyl groups (methyl or ethyl as far as this class goes).

3. Number the carbons on the chain starting from the side closest to an alkyl group. Each alkyl group will get a prefix of the number associated with the carbon it is bonded to, even if there is more than one of that kind of alkyl group. But instead of writing out “methyl” two times if the alkane has two methyl groups, it is numbered with the appropriate Greek prefix (in this example, it would be di- for two). The numbers associated with the positions of the carbons are written in front, with commas separating them from each other and a dash separating them from words.

4. When both of the alkyl groups we're dealing with are present, number each group and list them in alphabetical order in the name.

Examples:








Naming Cycloalkanes:

Cycloalkanes are saturated hydrocarbons with rings. Their skeletal structures are geometric shapes where the corners represent carbon atoms assumed to be bonded with hydrogens.



1. As far as this class goes, there will either be an ethyl group or a methyl group (or multiples) attached to the ring. If there is only one, there is no need to give it a prefix.

2. When there are two alkyl groups, alphabetize them. The one that comes first alphabetically is given the first spot, and the carbons are numbered in the direction that will give the smallest number for the second substituent (so number towards the shortest path to the second alkyl group).

3. If there are more than two substituents, number in a way that yields the smallest numbers possible in the finished name. If there are identical sets of numbers, use alphabetical priority.

Examples:




Naming Haloalkanes:

Also called alkylhalides/halogenated alkanes. They are alkanes with one or more halogens attached (F, Cl, Br, I).

1.
F = fluoro
Cl = chloro
Br = bromo
I = iodo

2. Halogen and alkyl substituents are considered of equal rank, go by alphabetical priority.

Examples:




Naming Alkenes and Cycloalkenes:

Alkenes and cycloalkenes have one or more carbon double bonds.

1. Replace the suffix -ane with -ene.

2. The parent chain will be the longest continuous chain of carbon atoms that contains both carbons of the double bond.

3. Number the parent chain from the end closest to the double bond.

4. Two numbers will be associated with the double bond, assign it the smaller one. This number will appear as a prefix to the parent chain name, with a dash separating numbers and words.

5. With cycloalkenes, number in the direction that gives the lowest numbers for substituents.

Examples:




Naming Alkynes:

Alkynes have carbon triple bonds. The rules are exactly the same as they are for the alkenes, except the new suffix is -yne.

Example:




Naming Alcohols:

Alcohols have hydroxyl groups: –OH

1. Name the longest parent chain that includes the hydroxyl group. The suffix for alcohols is -anol.

2. Number starting at the end closest to the hydroxyl group. The number associated with the hydroxyl group will appear as a prefix to the parent chain name, with a dash separating numbers and words.

3. Name and number the other substituents the same as before.

Examples: