Recently we had this challenge in our Organic Chemistry Department. I was not involved in it but I thought it might be interesting for the SE Chemistry site, so here it is.

Propose a structure for C20H18 with the longest IUPAC name. Following rules apply:

  1. Names must be generated with MarvinSketch: Structure>Generate Name…>Preferred IUPAC Name (https://www.chemaxon.com/products/marvin).
  2. No isotopic markings can be used.
  3. The structures must be possible (no cycles with too much unsaturations nor systems with impossible tension).
  4. All the characters will be counted: numbers, letters, points, colons, dashes, everything.
  5. Longest name wins.

Here is the example that was given:

enter image description here

and the name provided by MarvinSketch:


141 characters

Good luck and prosperous year 2018!


Well, what is a challenge without a prize? So, I have set a bounty worth +50 reputation for the longest name. Sorry, I can not spend much more on it. Remember that you can post more than one structure. If you have proposed one and after some days you find a structure with a longer name, you can post it too.

  • $\begingroup$ How is longest determined? By character count (e.g. using a mono-spaced font) or by the actual physical length using a proportional font. If a proportional font is used, which one? $\endgroup$
    – MaxW
    Dec 23, 2017 at 17:43
  • 2
    $\begingroup$ @mhchem You just edited a formula with HTML tags instead of using own package. Should we be worried? $\endgroup$
    – andselisk
    Dec 23, 2017 at 18:34
  • 4
    $\begingroup$ @MaxW Just the character count without spaces. Any text editor will do. $\endgroup$ Dec 23, 2017 at 18:53
  • 1
    $\begingroup$ @andselisk No. Don't worry. If its just 2 subscripts, <sub> does do its job quite well. I'd prefer the MathJax font would not look different to the text font, then I would. $\endgroup$
    – mhchem
    Dec 24, 2017 at 20:05

6 Answers 6


$\ce{C20H18}$, 246 characters

enter image description here


PIN: (1'R,1''R,1'''R,1''''R,1'''''R,1''''''R,2''''R,3''''S)-octaspiro[tetrakis(cyclopropane)-1,2':1',2'':1'',2''':1''',4''''-bicyclo[1.1.0]butane-2'''',2''''':1''''',2'''''':1'''''',2''''''':1''''''',1''''''''-tetrakis(cyclopropane)]-2,2''''''''-diene

  • 2
    $\begingroup$ This is very good. Your approach has given me some further ideas, so you're not safe yet! :< $\endgroup$ Jan 4, 2018 at 20:39

$\ce{C20H18}$, 153 characters


enter image description here

P. S. I guess someone should just start, so I simply used the slightly modified structure from the example. I'm pretty sure this one is going to be criticized a lot by experienced organic chemists, so it's more like a kick-starter.

I found it very useful to start with Avogadro first to sketch (and optimize, Ctrl+Alt+O) the initial geometry (very handy for the geometries which are distorted or resembling platonic solids), then import cml file to MarvinSketch and do the rest.

For those who would like to check the names, copy it from here, the press Ctrl+Shift+N, Ctrl+V and click Import in MarvinSketch. For the record, currently MarvinSketch 17.29.0 is being used.

  • 1
    $\begingroup$ Thanks for participating!!! We normally use ChemDraw but since MarvinSketch is free, I have set that one so that more people can participate. $\endgroup$ Dec 24, 2017 at 10:10
  • $\begingroup$ @RaoulKessels I agree that MarvinSketch might be not that advanced, but it gets the job done, free and is available virtually anywhere, so I fully support your choice:) $\endgroup$
    – andselisk
    Dec 24, 2017 at 10:12
  • $\begingroup$ Let's start nitpicking ;) Bonds directing over plane aren't placed properly, it seems. $\endgroup$
    – Mithoron
    Dec 24, 2017 at 22:40

$\ce{C18H20}$ : 145 characters

I was curious as to the isomer with the longest name that had actually been reported in the literature rather than hypothetically proposed (so we at least know it exists).

The IUPAC name, whilst not quite as long as some of the examples, is a respectable 145 characters, largely due to the representation of stereochemistry and connectivity.



The molecule was reported in a 2002 paper (J. Org. Chem. 2002, 67 4436–4440) on the rearrangements of a set of spiro[2.4]hepta-1,4,6-trienes

  • 3
    $\begingroup$ Are you certain that this PIN is correct? Also, this is $\ce{C18H20}$, not $\ce{C20H18}$ as in the OP. Still interesting, just bad luck. $\endgroup$ Dec 28, 2017 at 20:18

Here is my input with character count increasing up to down. I have added InChI codes because it seems MarvinSketch is less capable of reading names than it is in their generation.

1. $\ce{C20H18}$: 164 characters

enter image description here

  • InChI=1/C20H18/c1-11-3-4-12(2)17-16-9-15-13(11)5-6-14(15)18(17)20(16)10-19(20)7-8-19/h3-6,9,13,15H,1,7-8,10H2,2H3/b4-3-,17-12+/t13-,15+,20-/s2

  • PIN: (2'R,4''Z,7''S,11''S)‐3''‐methyl‐6''‐methylidenedispiro[bis(cyclopropane)‐1,1':2',14''‐tetracyclo[,13.07,11]tetradecane]‐1''(10''),2'',4'',8'',12''‐pentaene

2. $\ce{C20H18}$: 167 characters

enter image description here

  • InChI=1/C20H18/c1-11-3-4-12(2)17-16-9-15-13(11)5-6-14(15)18(17)20(16)10-19(20)7-8-19/h3-8,14-15,18H,2,9-10H2,1H3/b4-3-,13-11-/t14-,15+,18+,20+/s2

  • PIN: (2'S,2''R,3''S,7''R,11''R)‐3''‐methyl‐6''‐methylidenedispiro[bis(cyclopropane)‐1,1':2',14''‐tetracyclo[,13.07,11]tetradecane]‐1''(10''),2,4'',8'',12''‐pentaene

3. $\ce{C20H18}$: 169 characters

enter image description here

  • InChI=1/C20H18/c1-11-3-4-12(2)17-16-9-15-13(11)5-6-14(15)18(17)20(16)10-19(20)7-8-19/h3-6,9,14,18H,2,7-8,10H2,1H3/b4-3-,13-11-/t14-,18+,20+/s2

  • PIN: (1''S,2'S,4''Z,6''Z,10''S)‐6''‐methyl‐3''‐methylidenedispiro[bis(cyclopropane)‐1,1':2',14''‐tetracyclo[,13.07,11]tetradecane]‐2''(13''),4'',6'',8'',11''‐pentaene

4. $\ce{C20H18}$: 171 characters

enter image description here

  • InChI=1/C20H18/c1-11-3-4-12(2)17-16-9-15-13(11)5-6-14(15)18(17)20(16)10-19(20)7-8-19/h3-6,9,13,15H,1,7-8,10H2,2H3/b4-3-,17-12+/t13-,15+,20-/s2

  • PIN: (1''S,2'S,4''Z,6''Z,10''R,11''R)‐6''‐methyl‐3''‐methylidenedispiro[bis(cyclopropane)‐1,1':2',14''tetracyclo[,13.07,11]tetradecane]‐2,2''(13''),4'',6'',8''‐pentaene

5. $\ce{C20H18}$: 172 characters

enter image description here

  • InChI=1/C20H18/c1-11-3-4-12(2)17-16-9-15-13(11)5-6-14(15)18(17)20(16)10-19(20)7-8-19/h3-9,14-15,17-18H,2,10H2,1H3/b4-3-,13-11-/t14-,15+,17+,18+,20+/s2

  • PIN: (1''S,2'R,2''S,4''Z,6''Z,10''R,11''S)‐6''‐methyl‐3''‐methylidenedispiro[bis(cyclopropane)‐1,1':2',14''‐tetracyclo[,13.07,11]tetradecane]‐2,4'',6'',8'',12''‐pentaene


$\ce{C20H18}$, 290 characters

Heavily based on Daniel Bonniot de Ruisselet's idea, the two "spiraned" cyclopropane pairs next to ending cyclopropenes are fused to bicyclobutanes as well, allowing remaining methyls attachment to the ending cyclopropenes, thus also allowing more chiral centers.

enter image description here

  • PIN: (1S,1′R,1′′′S,1′′′′′R,2′′S,2′′′′S,3′S,3′′′S,3′′′′′S,4′R,4′′′R,4′′′′′R)‐2,3′′′′′′‐dimethylhexaspiro[cyclopropane‐1,2′‐bicyclo[1.1.0]butane‐4′,1′′‐cyclopropane‐2′′,2′′′‐bicyclo[1.1.0]butane‐4′′′,1′′′′‐cyclopropane‐2′′′′,2′′′′′‐bicyclo[1.1.0]butane‐4′′′′′,1′′′′′′‐cyclopropane]‐2,2′′′′′′‐diene

  • InChI=1S/C20H18/c1-7-3-15(7)9-10(15)17(9)5-19(17)13-14(19)20(13)6-18(20)11-12(18)16(11)4-8(16)2/h3-4,9-14H,5-6H2,1-2H3/t9-,10+,11-,12+,13-,14+,15+,16+,17-,18-,19+,20-

  • CXSMILES: [H][C@]12C@([C@@]11C=C1C)[C@]21C[C@]11[C@]2([H])[C@@]1([H])[C@]21C[C@@]11[C@@]2([H])[C@]1([H])[C@@]21C=C1C |c:6,32|

  • gzipped and base64 encoded molfile:


(All data according to MarvinSketch 18.23, image postprocessed in a vector image editor; name postprocessed chem.SE and other text editor - RS italicization and apostrophe to prime replacement.
Marvin obviously has some issues, importing the produced InChI string produces some unspecified centers, so I have generated ChemAxon SMILES, this when pasted produces different stereochemistry, so I have added a compressed MDL molfile as well)

Can someone beat 300 characters, by further modifications?


enter image description here **162 Characters

enter image description here

  • PIN:(1'S,2'S,6'S,7'R,12'S,14'S)‐7'‐methyldispiro[cyclopropane‐1,8'‐pentacyclo[,6.02,14.012,15]pentadecane‐ 13',1''‐cyclopropane]‐2,2'',3',9'(15'),10'‐ pentaene
  • I have used MarvinSketch 17.28.0 for generating pin.

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