Wize University Organic Chemistry Textbook > Intro to Orgo (Functional Groups, Drawing, Naming)

IUPAC Systematic Naming

IUPAC Systematic Naming

General Naming Rules

Identify and name the longest carbon chain
If present, assign stereochemistry (R/S or E/Z)
Identify and name any substituents on the carbon chain
Give these substituents the appropriate 'address' - i.e. which carbon atom they are bonded to
Add substituent names as a prefix to the carbon chain
Change suffix of the carbon chain if necessary (for functional groups)

Important Things to Consider

The length of the longest carbon chain (you may have to look for this!)
The types of C-C bonds in that chain
The functional groups incorporated in the chain
The priority of each of those functional groups

The Carbon Chain

The root of the name will always identified as number corresponding to the longest continuous chain of carbon atoms.

\begin{array}{ll}\#\text{ carbon atoms = root}&\\ \text{1 = meth-} &\text{6 = hex-}\\ \text{2 = eth-} &\text{7 = hept-}\\ \text{3 = prop-} &\text{8 = oct-}\\ \text{4 = but-} &\text{9 = non-}\\ \text{5 = pent-} &\text{10 = dec-}\end{array}

This carbon chain must include any C-C multiple bonds present in the molecule, as this will complete the name of the carbon chain.

Image illustrating IUPAC Systematic Naming Theory

The Substituents

Additional Considerations

Lower priority functional groups (alkyl groups, alkoxy groups and halides) that are attached to the carbon chain are listed before the name of the carbon chain.

Substituents that have similar priority as the ones listed above must be listed with the lowest possible numbering system, or 'address'. For example:

Going from left to right, the Cl has an address of 2. Going from right to left, the Cl has an address of 4. Since 2 < 4, we have a 2-chloro substituent - the name is 2-chloropentane.

If there is more than one substituent, then the two numbers combined must give the lowest possible numbers. For example:

Going from left to right, the Cl is on 3 and the Br is on 4. Going from right to left, the Cl is on 3 and the Br is on 2. Since 2,3 <3,4, we have 2-bromo-3-chloro. The name is 2-bromo-3-chloropentane.

If there is more than one substituent of the same type, then we don’t list them separately, instead we combine them with a prefix. Each number is separated by a comma (,). Also notice that the prefixes used are as follows:

\begin{array}{ll}\#=\text{ prefix}&\\ \text{1 = no prefix} &\text{6 = hexa-}\\ \text{2 = di-} &\text{7 = hepta-}\\ \text{3 = tri-} &\text{8 = octa-}\\ \text{4 = tetra-} &\text{9 = nona-}\\ \text{5 = penta-} &\text{10 = deca-}\end{array}

Functional Groups

These are higher priority groups that occur along the carbon chain. These often result in a modification of the suffix of the carbon chain. These also effect the 'addressing' of the chain, as many of these groups are terminal and must start on Carbon-1.

Examples: