Polarity and Optical Activity

[justadream]

1) TBR says that all optically active molecules are polar. Are all polar molecules optically active?

2) I know meso compounds have an internal plane of symmetry. So does this make them ALWAYS nonpolar?

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[Teleologist]

1) TBR says that all optically active molecules are polar.

This is only in the context of orgo. You can have optically active, non-polar, octahedral complexes (I'm not sure about all at once though). Consider the various conformers of SBr2Cl2F2. There exists pair of enantiomers for this compound. And there are non-polar conformers.

Are all polar molecules optically active?

No. Consider HF.

2) I know meso compounds have an internal plane of symmetry. So does this make them ALWAYS nonpolar?

Bruh can we be best friends since you just touched on my favorite topic in chemistry.

Answer is no though, mate. Consider the ternary interhalogen, IBrF2 - specifically - the conformer with the axial F-I-F configuration. This has some symmetry. Is it non-polar? No.

 

[justadream]

@Teleologist

I searched for the structure of IBrF2 and I found this:

http://chemistry.stackexchange.com/...s-repulsions-and-number-of-unique-bond-angles


Not really sure how accurate that is. I'm also a bit confused on how that actually looks.

Are there more "common" examples of meso compounds that are polar? (as in, ones that the MCAT might test)?

 

[Teleologist]

@Teleologist

I searched for the structure of IBrF2 and I found this:

http://chemistry.stackexchange.com/...s-repulsions-and-number-of-unique-bond-angles

That's right, bruh 😉. I drew that shizz bruh. It's symmetrical. Think of all the forces acting on the the iodines. They're identical. So you can actually fold the axial F-I-F bond in half (fold as to put F on top of F) and you'll find that the molecule's various parts lines up perfectly.

Are there more "common" examples of meso compounds that are polar? (as in, ones that the MCAT might test)?

Polar meso? How about meso-2,3-dichlorobutane?

 

[NextStepTutor_1]

Keep in mind what optically active means. For the purposes of the MCAT, optically active compounds are those that are chiral and not meso. So, as @Teleologist mentioned, a compound such as HF, while polar, is not optically active b/c it has no chirality.