Organic Chemistry

Introduction to Nomenclature

Figure 41Isobutane

Figure 42Neopentane

Above you see a carbon bonded to three and four other carbons.

Note: a methane group is called amethylgroup when it is bonded to another carbon

instead of a fourth hydrogen.−CH 3

The common system has naming convention for carbon chains as they relate to branching.

n-alkanesare linear

iso-alkaneshave one branch R 2 CH—

neo-alkaneshave two branches R 3 C—

Note: ”R” in organic chemistry is a placeholder that can represent any carbon group.

18.5 Constitutional isomers.

One of the most important characteristics of carbon is its ability to formseveral relatively
strong bondsper atom. It is for this reason that many scientists believe that carbon is the
only element that could be the basis for the many complicated molecules needed to support
a living being.

One carbon atom can have attached to it not just the one or two other carbons needed to
form a single chain but can bond to up to four other carbons. It is this ability to bond
multiply that allows isomerism.

Isomers are two molecules with the same molecular formula but different physical ar-
rangements. Constitutional isomershave their atoms arranged in a different order. A
constitutional isomer of butane has a main chain that is forked at the end and one carbon
shorter in its main chain than butane.