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Structure of Alkanes: Straight-Chain and Branched Alkanes

SECTION 20 - Intro to Organic Chemistry

"The Chemistry of Carbon"

The carbon atom is the cornerstone of Organic Chemistry, and it's an essential element in the biological world.

Carbon has the unusual ability to bond strongly to itself (rings or chains), creating a backbone from which many millions of organic compounds are derived.

Carbon also bonds strongly to other nonmetals such as O, H, N, S, and the halogens.


Organic Chemistry  =  the study of carbon-containing compounds and their properties.

these compounds typically contain rings or chains of carbons

the simplest of the organic molecules are the alkanes...


The Structure of Alkanes

Alkanes are saturated hydrocarbons.

Hydrocarbons  =  compounds comprised (primarily) of carbon and hydrogen.

Saturated  =  describes compounds in which all of the C—C bonds are single bonds, so each carbon is bonded to four other atoms.

All of the examples we'll see here today are saturated hydrocarbons.


Straight-Chain Alkanes

The example below shows the first 4 unbranched, straight-chain alkanes (n-alkanes)...

Naming Unbranched Alkanes

Branched Alkanes

At four carbons in length, not only do we have the straight-chain (unbranched) n-butane, but we begin to see branched isomers as well.

Check out the examples below:


Isomers of C4H10


Isomers of C4H10

Pictured above is the only branched structural isomer of butane.

It's official, IUPAC name is 2-methylpropane, but it also has a common name: isobutane.

When you get to a chain having five carbons, you can have 2 branched structural isomers.

The visualization of this can be found below:


Isomers of C5H12

Structural Isomers of C5H12

For C5H12, there are 3 structural isomers.

There's the straight chain isomer, n-pentane.

And there's the two branched-chain isomers,

    ➞ 2-methylbutane (isopentane),  and

    ➞ 2,2-dimethylpropane (neopentane).

As you might expect, the longer the carbon chain, the greater the possibiities for branching.

General Formula of Alkanes


Next up in our discussion of SECTION 20 - Introduction to Organic Chemistry, we'll talk about (and learn) the:

Rules for Naming Alkanes  :-)