I read in my book, that substituted allenes do not have chiral carbons, but actually the molecule is chiral, so they show optical isomerism. But what is the difference between them( chiral carbon and chiral molecule)?

  • $\begingroup$ The difference? They are about as different as two things can be. Chiral carbon is an sp3 carbon with four different substituents, and chiral molecule is a molecule that can be left or right, that is, does not coincide with its mirror image. Indeed, it is possible to have chiral molecules without chiral carbon or even without any carbon whatsoever. $\endgroup$ – Ivan Neretin Apr 1 '18 at 4:45
  • $\begingroup$ It is even possible to have a molecule containing several chiral carbon atoms, but which is not chiral itself. Such a molecule is called a meso compound. $\endgroup$ – Thomas Jungers Apr 1 '18 at 13:02
  • $\begingroup$ @Masrat : the post linked by Mithoron is a must read. Please do read it carefully, it will clarify many things. Very briefly, though, remember that chirality is a property of the whole molecule. And if your book really uses the term chiral 'carbon', rather than 'stereocenter' or 'stereogenic carbon', then it's probably not a very good book. Allenes can have stereogenic 'axes', but the main concept doesn't change: the whole allene molecule is chiral if it is not superimposable to its own mirror image. BTW, optical isomerism is a possible (not always observable/ed) consequence of chirality. $\endgroup$ – user6376297 Apr 1 '18 at 15:51
  • $\begingroup$ Thanks for explaining this, I will read the Mithoron link for sure. Thanks again! @user6376297 $\endgroup$ – Masrat Apr 2 '18 at 1:33

In addition to the excellent Mithoron link, heed Lord Kelvin.

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