| Author | Message | ||
     Lois Weyer (Lois_weyer) New member Username: Lois_weyer Post Number: 16 Registered: 7-2002 |
The spectrum of acetic anhydride is included in the Wiley/VCH collection and the Voegele and Buback VCH book, FT-NIR Atlas, from which the collection was derived. Perhaps you can find it in a library. It has a large series of peaks in the first combination region, 3983, 4033, 4117, 4157, 4210, 4356, and 4442, a smaller series in what might be the carbonyl second overtones, near 4660, 4760, 4850, and 5005, some in the CH first overtone region, near 5660, 5820, 5950, and 6010, and two more series observed with a longer pathlength, at 6881, 7296, 7416, and 8580 cm-1. The last peak is probably a CH second overtone and the others may be a second combination series. I haven't looked at the interpretation closely and am just giving you a rough idea. Hope this helps. | ||
| Rizwana (Unregistered Guest) Unregistered guest |
Can anyone tell me the charecteristic absorption bands of acetic anhydride.I am student doing a project | ||
| Paul Gemperline |
We have been developing tools for modeling NIR reaction spectra as a funciton of time and have observed an unusual absorbption band in mixtures of butanol and acetic anhydride at 1426 nm. This band does not appear in the any of the reactants nor in the reaction product, butyl acetate or acetic acid. Does anyone know what. I have sample spectra I can email to anyone who interested. | ||
| hlmark |
Paul - does the band form and then is constant, or does it follow an increase-decrease pattern, such as you'd expect from a reaction intermediate? If it's constant, then it might be due to the second harmonic of the -OH in the butanol, changed from it's usual frequency by hydrogen bonding to the AA. If it's a reaction intermediate, then you'd have to try to guess the structure, I think. I've been looking at the spectra in "The Handbook of Organic Compounds" and there are some compounds that have an absorbance band at or near that wavelength, although since I haven't seen the spectrum yet, I don't know if they look the same. But 2-ethylbutyric acid has a small band at 1425.8 nm, hexanoic acid at 1427.1, 2-ethyl hexanoic acid at 1427.7, formic acid at 1424.8, Butyric anhydride at 1425.7, 2-methyl-3-butyn-2ol at 1428.1, ethylene glycol monobutyl ether at 1426.1, 1-methoxy-2-propanol at 1429.1 (is that too far away?) Those were all in the first 50 pages of NIR spectra in that Handbook, but there are too many to go through them all. The handbook was designed to make it easy to find the spectrum of something where you know the structure (or name), but not the other way around. Nevertheless, there doesn't seem to be a shortage of molecules that absorb around that wavelength. If you send me the spectrum, I'll take another look, but I still don't think I'll be able to do do anything very much more thorough. Howard \o/ /_\ | ||
| Lois Weyer (Lois_Weyer) |
Paul, Howard has, as usual, been very thorough in his reply and I'm not sure I can add anything. Could you please send me the spectra anyway, so I can take a look? Lois ([email protected]) | ||
| Bruce H. Campbell (Campclan) |
Paul, Is there only one new band? There may be other new ones, hidden under others that usually show up. So, do any of the other bands show an unexpected increase? Alternatively, is there any decrease in the expected or usual bands? Bruce | ||
| Tony Davies (Td) |
Paul, If you want to (and it would be interesting) you could post the spectrum. Instructions are given in "formatting" (in left column of this page). Ian Michael showed an example in the discussion about water bands begun by Bob Forbes 27 Feb 03. An easy way to find it is to use the keyword search using "images". Best wishes, Tony | ||
| David W. Hopkins (Dhopkins) |
Paul, This is very exciting. I agree with Howard that you may have a signature of the forming of an intermediate, and I would like to see the time course of the 1426 nm feature, and the spectra of each of the pure reactants and products. How many of the intermediate scans do you have? Can you send the scans in Jcamp or spc format so we can really examine them? I think your program with your students is really interesting. Best regards, Dave [email protected] | ||
| hlmark |
Paul - I don't think that free -OH is likely to be generated, there's too much oxygen around that the various hydrogens can bond to for any to be left free. What seems more likely to me is that the hydrogens are bonding with a different amount of energy to a different species, i.e., from being bound to an oxygen in an -OH of a different BuOH, to being bound to an oxygen (either the =O or the -O- in the anhydride) that is different. In this case, we can expect the hydrogen to be attracted with different strengths and have different energy, and therefore vibrate differently. Especially the =O is likely to be very electronegative and therefore have a large attraction to a hydrogen atom. Howard \o/ /_\ | ||
| Lois Weyer (Lois_Weyer) |
Paul, A free butanol OH would be a doublet with the maximum at 1409 nm. I show the peak in Figure 8 of my chapter, which I'll send to you. The 1670 peak Bruce asked about is probably one of the methyl CH stretches of the anhydride. I've seen the same shift in nitrocellulose. Your spectrum of pure butanol appears to have stray light affecting it. The combination region is too low. Perhaps there was a bubble in your cell. The butanol spectrum is much stronger than the anhydride and therefore overwhelms the mixture spectrum. That's why the 2250-2300 nm peak appears to shift. I've seen water absorb at 1426 under some circumstances, although I can't imagine how water can be present with the anhydride there. Maybe there was some water in the butanol and it hasn't reacted yet? In general, I think I would agree with Howard, the 1426 nm peak is there because a hydroxyl (either the alcohol or water) is bonded to something other than itself. I've enjoyed the discussion and am glad that you posted the question. Lois | ||
| Gabi Levin |
Hi Everyone, Just see how everybody's ears are up when we are confronted with some exciting news. Still, after reading all comments I would say none before knowing the basic answer - was the peak time dependent or not. So, I will be glad to see the spectra, and to know more Gabi Levin Gabi Levin |