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Summary Sheet: Stereochemistry
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'
- Add substituent names as a prefix to the carbon chain
- Change suffix of the carbon chain if necessary (for functional groups)
Isomer Flowchart
Summary Sheet: Determining Maximum Number of Stereoisomers
There is a classic question you will likely come upon in your chemistry career. An example is shown below.
Example: What is the maximum number of stereoisomers possible for the following compound?
It is important to remember what classifies as a stereoisomer. It includes all versions of a compound with different chiral centres (e.g. R/S) and geometric isomers (e.g. cis/trans). In each of those cases, there are two options for each stereogenic centre: R or S (if a chiral carbon) and cis or trans (if geometric). So we can derive an equation for the total number of stereoisomers:
Number of possible stereoisomers = 2n, where n = number of stereogenic centres
Let's take the above example. First, we need to identify all the stereogenic centres:
In this case, n = 6. There are 4 chiral carbon atoms and 2 alkenes with cis/trans possibility. Therefore, the number of possible stereoisomers is 26 = 64. Wow.
As you might expect, there are exceptions to this rule. Be on the lookout for meso compounds! For every possible meso compound there is one less possible stereoisomer, since two enantiomers are now the same:
Example: What is the maximum number of stereoisomers possible for the following compound?
Summary Sheet: Nomenclature and Conformations of Alkanes and Cycloalkanes
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'
- Add substituent names as a prefix to the carbon chain
- Change suffix of the carbon chain if necessary (for functional groups)
