Introduction to Chemical Formulae
Organic Chemistry | Alkanes | Alkenes | Alkynes | Alkanols
Alkanoic acids | Esters | Alkanals | Alkanones | Further information

Methyl Groups

To any organic compound, a methyl (CH₃) group can replace a hydrogen.

For example, a methyl group can replace the hydrogen on carbon-2 of propane:

To name such compounds, a prefix is added. This prefix is n-methyl, where n is the number of the carbon to which the methyl group is attached. Therefore, the compound shown above is 2-methylpropane.

Isomers

Isomers are compounds with the same molecular formula, but different structural formulae.

For example, butane and 2-methylpropane both have the molecular formula C₄H₁₀ but have quite different structural formulae. Shown below are butane and 2-methylpropane.

Cycloalkanes and Cycloalkenes

Cycloalkanes consist of a carbon ring with two hydrogens attached to each carbon atom.

For example, cyclohexane has the molecular formula C₆H₁₂ and the structural formula:

Cycloalkenes are similar to cycloalkanes, but have a double bond between two consecutive carbon atoms in the ring. One hydrogen is lost from both carbon atoms.

For example, cyclohexene has the molecular formula C₆H₁₀ and the structural formula:

Chloro, Bromo and Iodo Groups

In a similar way to methyl groups being added to a compound, chlorine, bromine or iodine atoms can replace hydrogen atoms in organic compounds. They form, respectively, chloro, bromo and iodo groups. The compounds are named in similar way to on the addition of methyl groups, with a prefix of n-chloro, n-bromo or n-iodo added to the compound's name.

For example, 1-chloropropane has the following structural formula:

Incidentally, 1-chloropropane could also have be drawn out as shown below. The two diagrams show the same compound, not two isomers.