# What is the IUPAC nomenclature of alkane with large numbers of C atoms (more than 200)?

What is the IUPAC nomenclature for alkanes with large numbers of $\ce{C}$ atoms (more than 200)? For example, what is the IUPAC accepted name for $\ce{C_{205}H_{412}}$?

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The definitive answer is, of course, in the rules established by the IUPAC’s “Commission on nomenclature in organic chemistry”. The reference you are looking for is:

“Extension of Rules A-1.1 and A-2.5 Concerning Numerical Terms Used in Organic Chemical Nomenclature”, Pure Appl. Chem., 1986, 58, 1693-1696

which can be found here as a PDF and here as an HTML version. In particular:

NT-1.1 - The fundamental numerical terms for use in hydrocarbon names or as multiplying prefixes for simple features are given in the following list:

\begin{array}{|c:c|c:c|c:c|c:c|}\hline 1&\rm \mathsf{mono\hyphen~or~hen\hyphen^*} &10 &\rm \mathsf{deca\hyphen}&100&\rm \mathsf{hecta\hyphen}& 1000&\rm \mathsf{kilia\hyphen} \\\hline 2&\rm \mathsf{di\hyphen~or~do\hyphen ^*}&20&\rm \mathsf{icosa\hyphen}^{**}&200&\rm \mathsf{dicta\hyphen}&2000&\rm \mathsf{dilia\hyphen}\\\hline 3&\rm \mathsf{tri\hyphen}& 30&\rm \mathsf{triaconta\hyphen}&300&\rm \mathsf{tricta\hyphen}&3000&\rm \mathsf{trilia\hyphen} \\\hline 4&\rm \mathsf{tetra\hyphen}&40&\rm \mathsf{tetraconta\hyphen}&400&\rm \mathsf{tetracta\hyphen}&4000&\rm \mathsf{tetralia\hyphen} \\\hline 5&\rm \mathsf{penta\hyphen}&50&\rm \mathsf{pentaconta\hyphen}&500&\rm \mathsf{pentacta\hyphen}&5000&\rm \mathsf{pentalia\hyphen}\\\hline 6&\rm \mathsf{hexa\hyphen}&60&\rm \mathsf{hexaconta\hyphen}&600&\rm \mathsf{hexacta\hyphen}&6000&\rm \mathsf{hexalia\hyphen}\\\hline 7&\rm \mathsf{hepta\hyphen}&70&\rm \mathsf{heptaconta\hyphen}&700&\rm \mathsf{heptacta\hyphen}&7000&\rm \mathsf{heptalia\hyphen}\\\hline 8&\rm \mathsf{octa\hyphen}&80&\rm \mathsf{octaconta\hyphen}&800&\rm \mathsf{octacta\hyphen}&8000&\rm \mathsf{octalia\hyphen}\\\hline 9&\rm \mathsf{nona\hyphen}&90&\rm \mathsf{nonaconta\hyphen}&900&\rm \mathsf{nonacta\hyphen}&9000&\rm \mathsf{nonalia\hyphen}\\\hline \end{array}

So, $\ce{C_205H_412}$ is the molecular formula of pentadictane. $\ce{C_7547H_15096}$ is heptatetracontapentactaheptaliane.

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Presuming it is linear, then it should follow the trend of the higher alkanes.

For $\ce{C10}: \ce{CH3(CH2)8CH3}$ - the name is decane (deca means ten).

For $\ce{C20}: \ce{CH3(CH2)18CH3}$ - the name is icosane (icos means twenty)

For $\ce{C25}: \ce{CH3(CH2)23CH3}$ - the name is pentacosane

After icosane, the higher alkanes follow the following:

For $\ce{C30}: \ce{CH3(CH2)28CH3}$ - the name is triacontane

For $\ce{C40}: \ce{CH3(CH2)38CH3}$ - the name is tetracontane

For $\ce{C50}: \ce{CH3(CH2)48CH3}$ - the name is pentacontane

So...

For $\ce{C100}: \ce{CH3(CH2)98CH3}$ - the name would be decacontane

For $\ce{C200}: \ce{CH3(CH2)198CH3}$ - the name would probably be icosacontane

And for $\ce{C205}: \ce{CH3(CH2)203CH3}$ - the name might be pentacosacontane

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From wikipedia, the name for $C_{100}$ is hectane. – lambda23 Nov 18 '12 at 13:12
And I have learned something. – Ben Norris Nov 19 '12 at 2:23