Nomenclature in organic chemistry is based on a set of rules dictated by an organization called the International Union of Pure and Applied Chemistry (IUPAC). These rules describe the ways that you name the parent chain of an organic compound and the various substituents that can be attached to the parent chain.
This is based on the use of prefixes and suffixes that describe your molecule of choice.
To name a parent Chain:
For ALKANES: (Containing only single bonds to Carbons and Hydrogens)
Find and name the longest continuous carbon chain.
Identify and name groups attached to this chain.
Number the chain consecutively, starting nearest to the end that has the first substituent group.
Designate the location of each substituent group by a number and name.
Assemble the name such that the substituents appear in alphabetical order.
To Accomplish 1: Count the longest carbon chain.
# of Carbons Prefix # of Carbons Prefix
1 Meth 6 hex
2 Eth 7 hept
3 Pro 8 oct
4 But 9 non
5 Pent 10 dodec

For Alkanes add the suffix –ANE
Ie. 6 Carbon chain would be called hexane.
To Accomplish 2. Identify and name groups attached to this chain.
Carbon groups attached to the parent chain are identified as substituents. These are named by adding the base parent chain prefix followed by the suffix –YL.
Ie. a 2 carbon chain on Carbon 2 of hexane is called 2-ethylhexane.
If there are multiple substituents, you name them in alphabetical order. If there are more than 1 of the same substituent, (di – 2, tri – 3, tetra – 4).


Longest carbon chain here is 8 carbons, so it is an OCATANE.


There is a 2 Carbon group and two 3 Carbon groups attached here. Therefore, we name:
3-ethyl-4,5-dipropyloctane
Make sure that the numbering you choose is the lowest magnitude numbers. (ie. If you named this 6-ethyl-4,5-dipropyloctane, that would be incorrect).
Halogens can sometimes be substituents in organic compounds: These are called:
Fluoro – Fluorine
Bromo – Bromine
Chloro – Chlorine
Iodo – Iodine
Naming Alkenes and Alkynes:
The Ene Suffix indicates an alkene (double bond)
The longest carbon chain must include both carbons in the double bond.
The root chain must be number from the end nearest the double bond carbon. If the double bond is in the centre of the molecule, then choose numbering based on the substituents as you would in alkane naming.
If more than one double bond is present in the compound, it is named as a diene or triene or equivalent prefix – ene (you won’t get more than 3 double bonds to name).
In cycloalkenes (Cyclyzed alkenes) – the double bond is assigned carbons 1 and 2, where Carbon 2 is the nearest substituent to the double bond.
Some substituent groups that you may encounter on the MCAT: H2C=CH- Vinyl Group,
H2C=CH-CH2- Allyl Group
Sometimes you may encounter something that is cis or trans:

Cis implies that the top priority groups (as dictated by the Cahn-Ingold-Prelog rules that we discussed in class) are on the same side.
Trans implies they are on opposite sides.
Sometimes we also use E or Z designations as well to generalize this concept in a few more complicated cases :

In this case it is tough to decide cis or trans designations. So we look at each carbon separately and decide which is the highest priority group attached to that carbon. If they are on the same side of the double bond, its called Z (MCAT Protip: Za Zame Zide) . If it is on opposite sides its called E.

Alkynes (triple bonds) are named like Alkenes but use the suffix –yne. If there is both a double bond and triple bond in the molecule, it is labeled as an –en-yne. These have the same priority.
Ie. 6 Carbon chain with a double bond at carbon 2 and a triple bond at carbon 5
Hex-2-en-5-yne