Organic Formulation Theory: Alkanes

Saturated hydrocarbons, paraffins or Alkanes

They are called saturated hydrocarbons or alkanes all compounds made of carbon and hydrogen, which are of open-chain and have single bonds.

Straight-chain alkanes.

They correspond to the general formula C_nH_2n+2, being the number of carbon atoms n. They form a homologous series, sets of compounds with similar chemical properties and they differ in the number of carbon atoms in the chain.

Example:

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According to IUPAC rules, to name a linear alkanes are considered two cases:

• The first four compounds are named as follows:

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• The following compounds are named using as prefixes Greek numerals which indicate the number of carbon atoms in the chain, adding the ane end, which is generic and applied to all saturated hydrocarbons (hence the name alkanes).

Examples:

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The following compounds of the series are called tetradecane (14), pentadecane (15), hexadecane (16), heptadecane (17), octadecane (18), nonadecane (19), eicosane (20), eneicosane (21), docosane ( 22), tricosane (23), tetracosane (24), …, triacontane (30) …, tetracontane (40), etc.

Univalent radicals of saturated linear hydrocarbons.

Radicals are groups of atoms which are obtained by loss of a hydrogen atom from a hydrocarbon.

The radicals derived from alkanes by loss of a hydrogen atom from a terminal carbon are named replacing the termination ane by yl.

Examples:

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And so on.

To name a branched radical like this,

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It is considered that a methyl group attached to the radical chain, and to indicate the number that correspond to the carbon atom to which it is attached, the longest chain is numbered by assigning the number 1 to the carbon atom that has lost the atom of hydrogen. This number, called localized, is written before the name of the radical, separated from it by a hyphen.

Example. In the case above, the methyl group could be in the forms listed below and their names are as follows:

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Branched chain alkanes.

According to the IUPAC rules, to name branched chain alkanes we must proceed as follows:

• It is chosen the main chain containing the largest number of carbon atoms.
• It is numbered the chain chosen from one end to the other end, so that the lowest numbers to carbons are resumbered to chains which have side chains. The radicals are named before the main chain in alphabetical order.

Example:

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Note that:

• Firstly we number the main chain, starting the numbering as the indicated criterion.
• If the number of the main chain, starting from either end, the substituents are on the same numbers, the smallest of the first side chain is quoted in the name locator is assigned.
• Locators are written before the name of radical, separated it from by a hyphen.
• Only, they can accumulate locators refered to identical radicals. In this case, locators are separated by commas and the names of the radicals have the prefixes di, tri, tetra, etc.
• The radicals are named in alphabetical order, ranking last name of the backbone.

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In this case you can choose three chains with equal number of carbon atoms; when this occurs, it is chosen as the backbone having larger number of side chains. Therefore, the numbers and the name will be:

5-butyl-3,6-dimethylonane

In simple radicals it is not taken into account for the multiplicative prefixes alphabetical order. In the previous case we look at but and met, regardless of di.

The complex radicals (branched) are named in alphabetical order, given in that order multiplicative prefixes of complex radicals, they are written in parentheses.

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5-(1,2-dimethylpropyl)-4-ethyl-3-methylnonane

You can download the App BioProfe READER to practice this theory with self-corrected exercises.