[mmman]

So I'm pretty sure I got 5-iodovanillin. The melting point in the literature is 183-185 C and I got 182.7-183.5 C. But my NMR spectrum isn't showing the alcohol peak. It barely shows up on the SDBS spectrum also (http://sdbs.db.aist.go.jp/sdbs/cgi-bin/direct_frame_top.cgi). Does anybody know why this is?

[kriggy]

its because the OH protons are acidic and then can be substitued by deuterium from your solvent thus then being invisible

[mmman]

So the more acidic a proton is the less likely it will show up in your NMR spectrum?

[kriggy]

Something like that. I looked into the NMR database and it seems that your OH proton is hidden in that crazy-supper-almost invisible blob at about 10,1 ppm.
BTW any idea what causes those multiple peaks under 4ppm?

[Babcock_Hall]

When a peak is broad and low, the reason may be chemical exchange.  I sometimes see -OH peaks when the NMR solvent is CDCl₃, but not always.

[mmman]

Something like that. I looked into the NMR database and it seems that your OH proton is hidden in that crazy-supper-almost invisible blob at about 10,1 ppm.
BTW any idea what causes those multiple peaks under 4ppm?

Yea here's 10.1 ppm zoomed in and integrated. btw I used d-acetone so it makes since that the acetone would steal that hydrogen. I assumed the peaks under 4 ppm were left over vanillin, ethanol, ethyl acetate or water.