# Drawing the condensed structure of ethylcyclobutane

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?

• You don't draw condensed structures for rings. Draw the ring like a square and condensed the side chain. Commented May 4, 2017 at 15:54
• – user7951
Commented Jul 4, 2018 at 11:28

$\ce{CH3CH2CH(CH2)3}$ 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.

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:

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:

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

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.
• 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. Commented Jul 18, 2020 at 14:23

There is no exact definition, what condensed formula means. One might be able to condense the formula up to the following

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).
• Is it possible to condense it like $\ce{(C4H7)C2H5}$ Commented May 5, 2017 at 8:47
• @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. Commented May 5, 2017 at 8:57