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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: critzz on April 24, 2016, 04:33:50 PM

Title: chiral?
Post by: critzz on April 24, 2016, 04:33:50 PM
Regardless whether this compound could exist or not, would it be chiral?

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Title: Re: chiral?
Post by: discodermolide on April 24, 2016, 05:57:22 PM
What are the criteria used to determine if a molecule is chiral or not?
Title: Re: chiral?
Post by: critzz on April 24, 2016, 06:41:49 PM
That it's asymmetric. However, normally you can determine it very easily if there is a chiral carbon (when it has 4 different groups attached).
In this case the nitrogen is chiral, where the 4th group is a lone pair of electrons?
Title: Re: chiral?
Post by: AWK on April 24, 2016, 07:58:10 PM
This compound has two asymmetric atoms.
Title: Re: chiral?
Post by: Burner on April 24, 2016, 09:12:13 PM
Quote from: critzz on April 24, 2016, 06:41:49 PM
That it's asymmetric. However, normally you can determine it very easily if there is a chiral carbon (when it has 4 different groups attached).

There is a chiral carbon atom in this structure.
Title: Re: chiral?
Post by: critzz on April 24, 2016, 09:22:30 PM
Ah of course also the carbon at the back side... stupid of me  :P.

Maybe this is a better example of what I mean:

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So it's still chiral because the electron pairs of the nitrogen are fixed and can't scramble?
Then, would for example N-ethyl-N-methyl-propylamine be chiral at really low temperatures?
Title: Re: chiral?
Post by: Dan on April 25, 2016, 02:48:44 AM
Quote from: critzz on April 24, 2016, 09:22:30 PM
So it's still chiral because the electron pairs of the nitrogen are fixed and can't scramble?

You need to go back to the definition. Chirality is a property of a whole molecule, not a single atom. The presence of "chiral" centres does not necessarily confer chirality to the molecule (e.g. ribitol, galactitol etc. meso compounds in general). For this reason, I prefer the term "asymmetric centre" to "chiral centre".

A molecule is chiral if it has a non-superimposable mirror image. Draw the mirror image of your compound, are they superimposable?

A short cut is to look for a plane or centre of symmetry - if either of these are present, the molecule is achiral. Can you see any planes of symmetry in your molecule?
Title: Re: chiral?
Post by: critzz on April 25, 2016, 11:48:46 AM
Ugh, you are right, it possesses simple Cs-symmetry.

Last try then.

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The nitrogen in the front would be (R)-configuration and the nitrogen in the back (S)-configuration?
Title: Re: chiral?
Post by: Dan on April 25, 2016, 01:44:43 PM
Quote from: critzz on April 25, 2016, 11:48:46 AM
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The nitrogen in the front would be (R)-configuration and the nitrogen in the back (S)-configuration?

Yes, I think so.