[Sntna]

Hi, why do the two different meso compounds of 2,3,4-triol give different IR spectrums. Also, a racemic mixture should give the same IR spectrum as the individual enantimers yes?

[movies]

Start with the first part: what is the relationship of the two meso compounds?  What kind of isomers would you call them?  From there, what do you know about the physical properties that such isomers exhibit?

The second question is a little more complicated.

[AC Prabakar]

Hi, why do the two different meso compounds of 2,3,4-triol give different IR spectrums

Meso compounds means are they diastereomers to each?
If so IR may not be same at solid and liquid state as the physical properties of diastereomers are different.

If they are enantiomers to each,IR may not be same at solid state and may be same  liquid state.

Also, a racemic mixture should give the same IR spectrum as the individual enantimers yes?

I hope the above is partial answer for your second part.
The reason is the difference in the enantiomeric systems.

Basically there are three types of enantiomeric systems
1.Cogloromate system(Racemic mixture) 2.racemic compound 3.Pseudo racemate

For 1 and 3 IR at solid state will be same where as for 2 it Will vary at finger print region (u may not get corelation 0.99)
But in liquid state all will be same.
The same is applicable for PXRD also.

I hope that u may did IR at solid state.
Try it in liquid state!!!

[movies]

Meso compounds means are they diastereomers to each?
If so IR may not be same at solid and liquid state as the physical properties of diastereomers are different.

Yes, they are diastereomers and that means that they may have different physical properties.

If they are enantiomers to each,IR may not be same at solid state and may be same  liquid state.

This is not exactly correct.  The two pure enantiomers must exhibit the same physical properties and IR spectra unless they are interacting with something else that is chiral, such as plane-polarized light.

Also, a racemic mixture should give the same IR spectrum as the individual enantimers yes?

I hope the above is partial answer for your second part.
The reason is the difference in the enantiomeric systems.

This isn't quite right either.  In principle, racemates can exhibit different physical properties than either pure enantiomer.  You have it partially correct in that the origin of this difference comes from intermolecular interactions between the molecules.  The consequence of these interactions is to form diastereomeric complexes.  Imagine you have a racemic mixture of a compound; if the molecules tend to interact in some way (e.g., intermolecular hydrogen bonding) then you could end up with complexes of R–R, S–S and the mixed R–S interactions (assuming a 1:1 stoichiometry).  The R–R and S–S forms are enantiomeric, and therefore must exhibit the same properties.  If this is the prevailing form of intermolecular interaction, then the racemate and enantiopure compounds should exhibit the same IR spectra.  Now consider the R–S complex: it is a diastereomer of the R–R and S–S complexes and therefore may be different.  If the racemate favors a R–S complex, then the IR spectrum could be significantly different from that of the enantiopure compounds.  You really can't state with any certainty what will be different, nor how much it will differ.

AC has correctly identified that these intermolecular interactions are much more likely in a condensed state of matter (solid, neat liquid), but they can even exist in solution if the interactions are strong enough.  It is not a guarantee that a solution-phase IR of racemic and enantiopure compounds will be the same!

[AC Prabakar]

First i would like to say thanks for your valuable inputs.

If they are enantiomers to each,IR may not be same at solid state and may be same  liquid state.

This is not exactly correct.  The two pure enantiomers must exhibit the same physical properties and IR spectra unless they are interacting with something else that is chiral, such as plane-polarized light.

I too thought in the same way before reading the book "Enantiomers racemates and resolution by Jacques, J., Collet, A., Wilen, S.H.,1981, Wiley and Sons, New York" about two years ago (2008).

After studied this book only i came to know all above said things...

Pls go through the book if possible...
U can find more surprises like mathematical calcultions to identify the enantiomeric systems!!!(I too surprised at my first sight!)
In the same way only i fought with my boss to prove all the above said things about enantiomers....

Once again thank u for your inputs.

[movies]

I am a little confused about what you are implying now.  In principle, any compounds (even an achiral one) can have different IR spectra in the solid and solution phase.

I looked for that book, but we don't have it at our university library.  I may be able to get it at another library in town, but it is checked out right now.  I am curious to read what it has to say!

[AC Prabakar]

I am a little confused about what you are implying now.  In principle, any compounds (even an achiral one) can have different IR spectra in the solid and solution phase.

Yes your correct in the following conditions like
(1)the polymorphism,(2)impurities/level of other elements present in the particular compound etc.
But as long as above are same the IR will be same.
I am sure u will not have any change even in finger print region of IR and because of this property many industries using IR as a part of regular test(including pharmaceutical sector).

[movies]

Well, by definition of solid phase vs. solution phase, your second criterion is different!  Basically it comes down to different intermolecular interactions – either between analyte and another molecule of analyte (condensed phase), or the analyte interacting with solvent molecules (solution phase).