Alkanes are hydrocarbons that have only single bonds.
Before learning how to name alkanes, you need to understand different ways to draw and interpret them. There are three different ways to draw organic molecules: Lewis structure, condensed structure and bond-line structure.
Bond-line structures are used most often in organic chemistry. In a bond-line structure, carbons are not shown. Instead, ends of the lines and lines coming together represent carbons. Likewise, hydrogens that are attached to carbons are not shown but implied.
Alkane Nomenclature (How To Name Alkanes)
- Identify the parent chain
Find the longest continuous carbon chain(can be vertical, horizontal, etc). The name of the parent chain will start with a prefix signifying the number of carbons in the chain and end with “ane”
2. Number the parent chain
Locate groups attached to the parent chain. These groups are called substituents. Number the parent chain from the end closest to the first substituent. If there are multiple substituents in equivalent positions from both ends, start numbering from the end that has the substituent with lowest alphabetical order.
Left end of the parent chain is closest to the first substituent. Number from the left, substituent will get number 2. If we start numbering from the right, substituent will get number 3.
3. Name Substituents
Halogens (Group 17 elements) are named ending in “o”. Br= bromo, Cl = chloro, F = fluoro, I =iodo
Alkyl groups (hydrocarbons) are named using carbon prefixes ending in “yl”. CH3 =methyl, CH2CH3 = ethyl…
To name the substituent you must first write the number indicating the carbon it is attached to, followed by dash and the name of the substituent. For example 3-methyl means there is a methyl group attached to the third carbon on the parent chain.
4. Put the name together
First, you have to write substituents in alphabetical order followed by the name of the parent chain.
EXTRA NOTES
5. What to do if there are multiple same substituents on the parent chain?
Instead of writing every substituent out, you will need to group them together and use prefixes di(2), tri(3) and tetra(4).
For example, instead of writing 2-methyl-4-methylhexane, you will writing 2,4-dimethylhexane.
6. If there are two possible parent chains of equal length, select the one with most substituents.
7. Common names of complex substituents
8. What to do if there is a ring in the molecule?
If there is a ring attached to the molecule and the ring has less carbons than the chain, it will be considered a substituent. To name the ring, you have to write “cycle”+prefix for the number of carbons+ “yl”.
LINKS
Online Organic Chemistry Tutoring
References:
Organic Chemistry as a Second Language by David Klein
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