So for multiple bonds to be conjugated, they must be in an alternating double bond – single bond – double bond, etc arrangement. However, do they need to be continuous? In my textbook, they count the number of conjugated multiple bonds like this:

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However, for other molecules such as 9,10-Bis(phenylethynyl)anthracene :

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Would I count the number of conjugated multiple bonds as a total of 13 or as 7? In other words, do the bonds need to be continuous to be counted as conjugated pi bonds?

  • $\begingroup$ The total number of conjugated double bonds is 13: these bonds form groups of 7,3,3 conjugated bonds each in the anthracene and benzene rings respectively. $\endgroup$ – Aniruddha Deb Jan 4 at 16:50
  • $\begingroup$ The problem is in the geometry of the molecule. Are the two external phenyl groups coplanar with the anthracen central group ? $\endgroup$ – Maurice Jan 4 at 17:07
  • 2
    $\begingroup$ There's 15 conjugated pi bonds there and two perpendicular in triple bonds. What is the point of this question though? Illustration from book is for specific context - dependence of color of compounds with linear group of bonds. Other compounds behave quite differently. $\endgroup$ – Mithoron Jan 4 at 17:21

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