This is the IR spectrum of the adduct of Maleic Anhydride + alpha-terpinene (Diels-Alder reaction of the Diene from eucalyptus oil). I need to interpret this data for my results report. What are the important points (so I can make a table with it) and give a short interpretation of it? This is my first organic experiment, so I’m having a hard time interpreting the data. Thank you in advance!
The Correct Answer and Explanation is:
You’re very welcome! Here’s a guide to help you interpret the IR spectrum of the Diels–Alder adduct of maleic anhydride and α-terpinene, and present it clearly in a results report.
📊 Key IR Absorption Peaks Table
| Wavenumber (cm⁻¹) | Functional Group / Vibration | Interpretation / Significance |
|---|---|---|
| ~3050 | C–H stretch (alkene) | Indicative of alkene C–H bonds (if present) |
| ~2950 – 2850 | C–H stretch (sp³ alkane) | Shows saturated alkyl C–H stretching |
| ~1770 & ~1850 | C=O stretch (anhydride) | Strong double peak characteristic of anhydrides |
| ~1600 | C=C stretch (aromatic or alkene) | Present in diene before reaction; reduced after |
| ~1200 – 1300 | C–O stretch (anhydride) | Confirms presence of cyclic anhydride group |
| ~1000 – 1100 | C–O stretch (ether or alcohol, if present) | Could support ring closure or oxygen function |
🔍 Short Interpretation for Results Section
The IR spectrum of the adduct formed by reacting maleic anhydride with α-terpinene via the Diels–Alder reaction provides key structural evidence confirming the formation of a cyclohexene derivative bearing a succinic anhydride group. One of the most significant features is the presence of two strong carbonyl absorption bands around 1770 and 1850 cm⁻¹, which is typical of a cyclic anhydride. These peaks confirm that the anhydride moiety from maleic anhydride is retained in the product and has not hydrolyzed.
A broad set of peaks between 2950 and 2850 cm⁻¹ correspond to sp³ hybridized C–H stretching vibrations, indicating the saturated nature of much of the carbon framework in the product. This supports the expected cycloaddition that converts the diene and dienophile into a saturated ring.
The peak around 1600 cm⁻¹, which would represent an alkene (C=C) stretch in the starting materials, is significantly diminished or absent in the adduct. This supports the loss of the diene’s double bond system during the Diels–Alder reaction.
Additional peaks around 1200 to 1300 cm⁻¹ correspond to C–O stretching, which, along with the strong anhydride carbonyl bands, further supports the presence of a cyclic anhydride functional group.
Overall, the spectrum confirms that a Diels–Alder cycloaddition has occurred and that the anhydride group is intact in the final product.
