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The IUPAC name for this is ethylcyclobutane. I know that the formula is $\ce{C6H12}$.

I have no problems drawing the skeletal structure, but I have a little difficulty drawing the condensed structure. I know this is basic, but I just started learning how to name them.

I tried it below. For $\ce{CHCH2CH3}$, am I right to write it in a straight chain?

ethylcyclobutane

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3 Answers 3

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$\ce{CH3CH2CH(CH2)3}$ is the best you can do.

If you want to draw the cycle, then you should make it pendant, drwing a bond from the ring to the ethyl group.

enter image description here

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TL; DR: In order to unambiguously denote both branching and cyclicity in a condensed structural formula, a linear formula should include a notation for connectivity, like such:

enter image description here

There is a special notation (external linker, like in mykhal's answer) for the bridging atoms with connectivities of three and higher in IUPAC's Nomenclature of Inorganic Chemistry [1, pp. 26–27]:

IR-2.3.4 Special bond indicators for line formulae

The structural symbols $\require{HTML} \style{display: inline-block; transform: rotate(90deg); font-size: 3em}{\Large ~~~[~~}$ and $\require{HTML} \style{display: inline-block; transform: rotate(-90deg); font-size: 3em}{\Large ~~[~~~~}$ may be used in line formulae to indicate bonds between non-adjacent atom symbols.

Examples:

Examples 1-2

Examples 3-4

With this in mind, I'd like to propose the following condensed formula for ethylcyclobutane:

enter image description here

I used a dirty hack by utilizing a redox macros from the $\mathrm{\LaTeX}$ package chemformula without arrows which are supposed to denote electron flow:

\documentclass{article}
\usepackage{chemmacros}
    \chemsetup{
        modules = {all},
    }

\begin{document}

\ch{\OX{a,C}H(CH2CH2\OX{b,C}\redox(a,b)H2)CH2CH3}

\end{document}

References

  1. IUPAC “Red Book” Nomenclature of Inorganic Chemistry, 1st ed.; Connelly, N. G., Damhus, T., Hartshorn, R. M., Hutton, A. T., Eds.; IUPAC Recommendations; Royal Society of Chemistry: Cambridge, UK, 2005. ISBN 978-0-85404-438-2.
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    $\begingroup$ Nice catch. Unfortunately no such bond indicators are defined in IUPAC recommendations for organic chemistry. I guess if they were, maybe the slightly confusing parentheses would be optional for such simple cases. $\endgroup$
    – mykhal
    Commented Jul 18, 2020 at 14:23
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There is no exact definition, what condensed formula means. One might be able to condense the formula up to the following

enter image description here

UPDATE

  • Note that I use nonrecommended parentheses type for repeating unit (see e.g. here),
  • and see Andselisk's answer for the graphical bond indicator recommendation (in a different branch of chemistry, though).
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  • $\begingroup$ Is it possible to condense it like $\ce{(C4H7)C2H5}$ $\endgroup$
    – Pritt says Reinstate Monica
    Commented May 5, 2017 at 8:47
  • $\begingroup$ @PrittBalagopal, (C₄H₇)C₂H₅ formula is not bad. It is not totally unambiguous, but other compounds it might mean, like "ethylbutene" would have different more appropriate condensed formula. $\endgroup$
    – mykhal
    Commented May 5, 2017 at 8:57

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