[Mocook]

By any chance does anyone know where to obtain the UV spectrum of
alpha-Bromo-p-xylene
 or you have it would be great if you can post it.

For some reason i cannot find it

regards

[Arkcon]

Finding the UV spectrum of every obscure organic compound is going to be difficult.  People don't use UV-Vis spectra to identify every organic molecule, and it would somewhat of a waste of resources, to publish every spectrum in a set of books, or store all the images online.  Look at it this way:  you need 'α-bromo-p-xylene' on a page, someone else needs 'p-xylene', someone else needs 'β-chloro-ortho-xylene' ... are these molecules so strikingly different from the UV-Vis absorbance of benzene that we need a page for each one and every other possible permutation?  Yes, there are books of IR spectra, but sometimes we just list the major IR absorption ranges of functional groups to save space.  If you need this specific data, you will probably need to get a pure sample, and scan it yourself.

[Mocook]

I agree, okay now that you put it that way. would an addition of a bromine yield a red shift in the Uv spectrum of compounds, or is that not a general trend ?

[Corribus]

If the bromine is attached direct to the aromatic ring, then yes there will be a shift.  E.g., compare lowest energy maximum of orthobromotoluene @ ~274 nm (Chemical Physics 287 (2003) 285–294) to the lowest energy maximum of toluene  @ 266-268 nm (http://webbook.nist.gov/cgi/cbook.cgi?ID=C108883&Units=SI&Mask=400#UV-Vis-Spec).

If attached to a subtituent (e.g., the methyl group of toluene), I imagine that probably very little shift will be observed unless the experiment is done in the gas phase.  Effect on fluorescence (particularly the quantum yield) due to bromine substitution will be much greater than shift in UV-Vis absorbance, but again the effect will probably be much more pronounced when the bromine is substituted directly on the aromatic ring.

[Mocook]

that was the exact answer i was looking for, i got a shift on a substituent that was pretty minor, seems pretty accurate to my reaction.

Thank you!

[Babcock_Hall]

If your library has a a paper copy of the Sadtler standard spectra, which is compendium of UV/VIS spectra, you may be in luck.  It has thousands of compounds.