January 24, 2022, 05:56:15 AM
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Topic: Helical Chirality  (Read 178 times)

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Offline ConfoundedBrachiosaurus

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Helical Chirality
« on: January 12, 2022, 04:13:32 PM »
After first learning this definition of chirality, I cannot make any sense of the images or previous descriptions of how it works. Both the S and R enantiomers look the same to me.

Thank you in advance.

Offline Babcock_Hall

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Re: Helical Chirality
« Reply #1 on: January 12, 2022, 05:41:09 PM »
I am not sure what your question is yet.  Are you asking about R versus S configurations (suggested by the body of your opening post), or are you asking about the chirality of helices (suggested by your title)?  Also, do you know the definition of enantiomers?

Offline Borek

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Re: Helical Chirality
« Reply #2 on: January 12, 2022, 06:43:25 PM »
That's because helical chirality doesn't work on atom level (where RS makes sense), but on the whole molecule level - there is no atom to which the asymmetry can be assigned.

IOW: you need to take a step back :)
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Offline rjb

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Re: Helical Chirality
« Reply #3 on: January 13, 2022, 06:34:15 AM »
I have to admit that I had to look up 'helical chirality' as it's a term I hadn't heard before, but it is a familiar concept normally referred to as Axial chirality in my country, hence my consternation!

A lot of people struggle with getting their heads around 3 dimensional structures and chirality. One tool that I would recommend for all chemists (especially those who struggle to visualise 3D form) is a molecular modelling kit - this will help. By making physical models of the chiral forms, you should be able to see that the chirality exists not at a stereogenic centre but along one axis of the module, hence the term axial chirality.

If you're thinking about true helices (i'm not sure whether you are or not), then the models you might need to construct will probably take too long to put together unless you have loads of patience. In which case, have a look at a screw or a drill bit if you have one to hand. Hold it pointy side down between 2 fingers and begin twist it clockwise (when viewed from above). The screw moves downwards towards the floor right? Turn the screw pointy side up and when you turn it clockwise from above it still moves downwards towards the floor. Could you envisage a screw with a reversed (or left handed) thread; one that moves upwards rather than downwards as you twist it clockwise? How would that differ?


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