[rleung]

Hey,

I am having trouble seeing how the following structure is meso.  I have made structures and still cannot see it.  Can somebody please explain if you have time?  Thanks so much.

Ryan

[Winga]

Simply to do, draw its mirror image and see whether the image can superimpose the original one.
Turn the mirror image upside down...

This compound doesn't have plane of symmetry, but centre of symmetry.

Locating each of the atoms after moving them from x,y,z positions to -x,-y,-z positions (vice versa), if each of them is identical, then, there is a centre of symmetry.

[movies]

Recall that the definition of a meso compound is that it is an achiral member of a set of diastereomers in which some members are chiral.  This does not require the presence of a plane of symmetry, although that is the most common feature in meso compounds.  These inversion center meso compounds are tough to spot!

To reiterate on Winga's example above, drawing the mirror image and trying to superpose it will always tell you whether the molecule is chiral or not.  It's a good starting point.

[rleung]

Thanks.

Ahh, I am sorry to seem so stupid, but I still cannot see it The two structures you have are not superimposable.  I assume that the substituents that point up are facing toward me, while the substituents that point down are facing away from me.  If that assumption is correct, I cannot see how they are superimposable, because they are not..

Ryan

[Mitch]

Yes they are superimposable look harder.

[movies]

If you have a model kit, build a model of each mirror image.  It's often easier to see in 3D than on the page.

[bedlam17]

To superimpose, flip the one on the right forward to make it upside down.

[Winga]

Try this one!

[alphahydroxy]

if you're still not getting it, think about a point in the centre of the ring - this is the centre of symmetry. now, take one of the bromines and draw a line through the centre of symmetry to a point an equal distance out the other side. what's there?  it's another bromine..

try it again with the methyl group.... a stright line through the centre of symmetry takes you from one methyl to the other....

thus this is a meso compound, as there is an element of symmetry - just not a plane.

[Winga]

All atoms (including hydrogen and carbon) are needed to check.

[movies]

All atoms (including hydogen and carbon) are needed to check.

Nice picture!!

[nkaspirin]

so why not just labelling each chiral carbon atoms.
and it's meso....

[rleung]

Thanks so much for the *delete me*  I finally see it after building model after model.  I am still getting the hang of building these things since I didn't get them in the mail until last week (before that, I was relying totally on visualization).  I think I will be working with models in stereochemistry more often now, haha.  Thanks again.

Ryan