I don't understand why it's chiral. It's not like any of the phenyl

  • #1
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I don't understand why it's chiral. It's not like any of the phenyl rings are stuck in a single resonance structure.
 

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  • #2
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http://en.wikipedia.org/wiki/Hexaphenylbenzene

Take a look at the crystal structure. The phenyl groups are all angled the same way. If you turned them all the other way, the two structures would not be superimposable. The same concept is seen in left- and right-handed propellers (see picture).
 

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  • #3
Borek
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The phenyl groups are all angled the same way.
I think you have missed the point - phenyls can oscillate freely in some range of angles, so they are not chiral in a stable way, they can easily switch between right- and left- handed propeller shape. Questions is - what makes them "select" one of the chiral conformations.

According to the information on the wiki page hexaphenylbenzene is not chiral in the gas phase. My bet is that the propeller shaped molecule has lower volume and better contact surface and crystallizes easier - and once it starts to crystallize it just attracts other molecules in exactly the same conformation. But that's just a guess.
 
  • #4
DrDu
Science Advisor
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Classical case of spontaneous symmetry breaking. Crystallization of SiO2 melts leads also either to D or L quartz.
 

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