#iupac

Hi guys! This is a fast summary for the ones that find the IUPAC Nomenclature difficult, I hope it is useful.

The Basic Rules You Need to Know

The Longest Chain Rule. It basically means you need to count the carbons in the chain(s). The chain with the largest amount of carbons is the "parent", which means you will name the compound based on the number of carbons present.

The Lowest Set of Locants. It means you must count the atoms in the chain and name them based on which number would be the smaller for the substituent. Basically, if counting from left to right your substituent is in 2, but in right to left is in 4, you must count from left to right as 2 is smaller than 4.

Multiple Instances of the Same Substituent. It means that if you have the same substituent more than once in the chain, you must put a suffix that says so. Ex, you have to methyls then you would put dimethyl.

The naming of different substituents. If you have more than one substituent in your compound, you'll put the names in alphabetical order. Ex, ethyl would go first than methyl.

Naming different substituents present in the same position. If you have two substituents in the same carbon, put the number of the carbon + a comma. For example, 3,3-methyl.

Naming Complex Substituents. If a substituent has a branch with another substituent, name it as an alkyl group and put it in brackets.

Roots to name the parent chain:

Substituents:

Examples from my own notes:

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Before proceeding on the steps on how to correctly name and identify alkanes, alkanes should be defined first. Alkanes are hydrocarbons which can only form a single bond unlike alkenes and alkynes which can form double and triple bonds respectively. The IUPAC Nomenclature are the guidelines that are needed to be followed in order to name the alkanes. Take note that the first ten alkanes should be memorized because most of them appear in different IUPAC names. The IUPAC system requires to have names for the unbranched chains and next will be the names for the attached simple alkyl groups. Alkyl groups are named by replacing the suffix "-ane" to "-yl".

Here are the most common alkyl groups:

                                                        source

And now, we can finally proceed to the IUPAC rules regarding alkane nomenclature. The process begins with:

1. Find the longest chain of the carbon atoms as this will give you the name of the parent chain.

Example:

In the figure below, the longest chain is six carbons therefore the parent chain is hexane.

2.  If two chains have the same number of carbons, choose the chain with the most substituents.

3. Number the carbons in the chain starting from the end nearest the first substituent.

Example:

In this structure, we will name the carbons from left to right because is it nearer to the first substituent.

4. If there are substituents that are the same number of carbons in from either end, start the numbering from the end nearest the next substituent

5. Multiplying prefixes are used when a substituent appears more than once. There are also no spaces in the final name.

Example:

There are three instances of the methyl substituent in this alkane therefore it will be called trimethyl.

6. Halogen substituents are given priority in naming