[boodyx1]

how can i differentiate betn the following by IR and UV :
-ortho & para substituted in benzene ring
-axial & equatorial  substituted in cyclohexane
plz help me

[bromidewind]

Both ortho and para substituted benzene will be in the same IR region as just plain benzene, but the absorbance will be different. Try to deduce which will absorb more or less IR light. Axial and equatorial substitution in cyclohexane will appear the same.

As for UV, which is looking more at the actual number of functional groups than their conformations, neither of them will show up in your average UV spec. Both of them are <200 nm, which is the minimum threshold for most. If you have the equipment, cyclohexane will show up around 155 nm and benzene will show up around 178 nm. If you have additional groups, they may show up in the normal UV spectrum. As per your question though, neither of them will show any difference based on their conformations.

[boodyx1]

how can i differentiate betn the following by IR and UV :
-ortho & para substituted in benzene ring
-axial & equatorial  substituted in cyclohexanone
plz help me

[Train]

In UV, benzene and substituted benzenes have a weak absorption band around 255 nm.  This band can be affected by substitution and the effect of ortho and para substitution will be different.

In IR, you can sometimes tell the substitution pattern of substituted benzene based on the
band(s) around 900-675 cm^-1.

[bromidewind]

Insert Quote
In UV, benzene and substituted benzenes have a weak absorption band around 255 nm.  This band can be affected by substitution and the effect of ortho and para substitution will be different.

In IR, you can sometimes tell the substitution pattern of substituted benzene based on the
band(s) around 900-675 cm-1.

Thanks for that tidbit of info about UV. I didn't know that, and assuming its correct, I'll store it away in the random bits of information useful at one point in time area of my brain.

As for IR, most common spectrometers don't accurately measure below 1000 cm^-1. At least the FT-IR unit we use doesn't.

And I would say that the most accurate method overall of determining ortho/para/meta substitution on a benzene derivative is through H-NMR.

[PolymerKnowHow]

Perhaps this link will help:

http://www.chem.ucla.edu/~webspectra/ircomp.html

[Train]

Perhaps this link will help:

Cool link.  You can see the features I was refering to by comparing the spectra of ortho-, meta-, and para xylene.  o-xylene has a sharp, strong peak at about 740 cm-1, p-xylene has a sharp strong peak at about 800 cm-1, and m-xylene has two peaks in the same region.

My reference for the statements on both IR and UV is Silverstein et al, Spectrometric Identification of Organic Compounds.  However, you have to find 5th edition or earlier to get the chapter on UV.