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I was drawing out all the isomers of $\ce{C5H8}$ and came upon two structures of cyclopropane attached with double bonds. The group is neither a methylene nor an ethyl... what is it? What are the names of these two molecules?

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ethylidenecyclopropane Ethylidenecyclopropane

vinylcyclopropane Vinylcyclopropane (or Ethenylcyclopropane)

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  • $\begingroup$ Note that these aren't the IUPAC names, care to add those as well? Also a bit about how the two functional groups have (common) names as ethylidene and vinyl respectively. Thanks :) $\endgroup$ Aug 9 '12 at 8:16
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    $\begingroup$ Ethylidenecyclopropane is the IUPAC name for that molecule. What else could you call it? See acdlabs.com/iupac/nomenclature/93/r93_271.htm. The vinyl substituent has been recently accepted by IUPAC (in the last 10 years), but I haven't found supporting proof on the web. $\endgroup$
    – Ben Norris
    Aug 9 '12 at 10:57
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    $\begingroup$ As a side note, IUPAC names are nice and all, but completely worthless if practicing chemists do not use them: 2-propanone, methanoic acid, and 1,2-didehydrobenzene are all significantly more frequently referred to by their common names of acetone, formic acid, and benzyne. $\endgroup$
    – Ben Norris
    Aug 9 '12 at 11:04
  • $\begingroup$ @Manish, as already noted, "ethylidene" is in fact valid IUPAC nomenclature. $\endgroup$
    – user95
    Aug 17 '12 at 15:44

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