IUPAC Nomenclature of Alkanes: Part 1

IUPAC Nomenclature of Alkanes, Part 1

The video introduces line notation and the basic IUPAC rules for naming straight-chain and branched alkanes.

Line notation

• In organic chemistry, molecules are often drawn using line notation rather than showing every atom.
• Each endpoint and vertex represents a carbon atom.
• Hydrogens attached to carbon are omitted; the drawing implies enough hydrogens to give each carbon its usual four bonds.
• The zigzag shape reflects the tetrahedral geometry of sp³-hybridized carbons in alkanes.
• Wedge bonds indicate bonds projecting toward the viewer; dashed bonds indicate bonds projecting away from the plane.

Alkanes and their names

• A hydrocarbon contains only carbon and hydrogen.
• An alkane is a saturated hydrocarbon: its carbon atoms are connected by single bonds, with no carbon–carbon double or triple bonds.
• Alkane names use the suffix -ane. The prefix indicates the number of carbons:

Number of carbons Prefix 1 meth- 2 eth- 3 prop- 4 but- 5 pent- 6 hex- 7 hept- 8 oct- 9 non- 10 dec-

For example, a five-carbon alkane is pentane.

Naming the branched alkane shown

1. Find the longest continuous carbon chain. This is the parent chain.
2. Number the chain from one end. Choose the direction that gives a substituent the lowest possible number.
3. Identify and name each substituent. A one-carbon branch is methyl; a two-carbon branch is ethyl. Larger branches use the corresponding carbon prefix with the ending changed to -yl.
4. Give the substituent’s position, then combine it with the parent-chain name.
5. In the example, the longest chain has four carbons, so the parent is butane. Numbering from the nearer end places the one-carbon branch on carbon 2, making the molecule 2-methylbutane.

These naming rules are conventions established by IUPAC so that chemists can communicate a molecule’s structure consistently and unambiguously.

Speaker and source

• Professor Dave — the sole speaker and source in the subtitles.