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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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up vote 21 down vote accepted

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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3  
From wikipedia, the name for $C_{100}$ is hectane. – lambda23 Nov 18 '12 at 13:12
2  
And I have learned something. – Ben Norris Nov 19 '12 at 2:23

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