[HailoMan]

Hi all,

I am trying to assign peaks on IR spectra done on Gamma-Valerolactone (GVL) containing carbon nanotubes (CNTs).
I've dropped coated a KBr card with GVL-CNTs mix and obtained the FTIR with Bruker Vertex 70.
I found a number of papers reporting downshift of carbonyl in amides when mixed in solvents with high acceptor number). I suspect the peak at 1740 cm-1 is a result of such interaction.

However, I can't see much evidence of an upshift in carbonyl peak (1767 cm-1) to a higher wavenumber.
A few possibilities that I thought of:
- Perester formation (peaks often reported around upper 1700 cm-1 region). I tested the CNTs - GVL mix with a peroxide strip and could not detect any perester (lowest detection limit of the strip is 0.5 mg/L).
- GVL hydrolyses to gamma-hydroxyvaleric acid. However, looking at FTIR data of Gamma-butyrolactone vs. Gamma-hydroxybutyric acid, the ring opening seems to result in downshift of the carbonyl peak.
- Ink from the KBr card that I used?!?! I haven't tested whether this may be the case.

Anyone has any idea what the peak at 1819 cm-1 may be?
Any pointers would be much appreciated.

[Arkcon]

You question is a little to advanced for me, but maybe you'll have more responses in this sub-forum

[HailoMan]

Thanks Arkcon.

I've done a bit more reading into it and I think the peak may be coming out of alpha-angelica lactone.
To my understanding, a lot of commercial GVL is synthesized by catalytic hydrogenation of levulinic acid. Incomplete hydrogenation (or high synthesis temperature) will result in alpha-angelica lactone residue being present.

While this is the most likely possibility, the peak positions do not seem to match.
Carbonyl peak for alpha-angelica lactone had been reported at 1809 cm-1 (Jones, 1959) though the Spectral Database of Organic Compound (sdbs.db.aist.go.jp) reported peak at 1798 cm-1. The peak I observed in my run is somewhat higher at 1820 cm-1.

Jones, R.N., et al., Canadian Journal of Chemistry, The carbonyl stretching bands in the infrared spectra of unsaturated lactones, 37, pp. 2007-2022.