- #1
Harrisonized
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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.
I don't understand why it's chiral. It's not like any of the phenyl
- Thread starter Harrisonized
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- Chiral
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Discussion Overview
The discussion centers around the chirality of hexaphenylbenzene, exploring the reasons behind its chiral nature despite the phenyl rings not being fixed in a single resonance structure. Participants examine the implications of molecular conformation and crystallization on chirality.
Discussion Character
- Debate/contested
Main Points Raised
- One participant questions the chirality of hexaphenylbenzene, noting that the phenyl rings are not fixed in a single resonance structure.
- Another participant references the crystal structure of hexaphenylbenzene, suggesting that the consistent angling of the phenyl groups leads to non-superimposable structures, drawing an analogy to left- and right-handed propellers.
- A different viewpoint argues that the phenyl groups can oscillate freely, implying that they are not stably chiral and can switch between conformations. This participant speculates that the molecule may select a chiral conformation during crystallization due to lower volume and better contact surface.
- One participant introduces the concept of spontaneous symmetry breaking, relating it to the crystallization process of SiO2 and its resulting chirality.
Areas of Agreement / Disagreement
Participants express differing views on the chirality of hexaphenylbenzene, with no consensus reached on the stability of its chiral conformations or the mechanisms behind its chirality.
Contextual Notes
There are unresolved assumptions regarding the stability of phenyl group conformations and the conditions under which chirality is established during crystallization.
- #2
aroc91
- 181
- 5
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
Mentor
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aroc91 said:
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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