Answer Key Summer 2002
Spectrum 1: Citral (3,7-dimethyl-2,6-octadienal)
| Frequency | Assignment |
| 3020 | n(CH, sp2, aromatic) |
| 2952 | n(CH, sp3, alkane) |
| 2750, 2850 | n(CH, aldehyde) |
| 1690 | n (C=O, conjugated) |
| 1640 | n (C=C, alkene) |
| 1450 | d(CH2, CH3, bend) |
| Frequency | Assignment |
| 3500-2500 | n(OH, carboxylic acid) |
| 1680 | n (C=O, conjugated) |
| 1600, 1500 | n(C=C, aromatic) |
| 750 | n (CCl, stretch) |
Note: The presence of certain CH-groups is difficult to prove if teh area is dominated by a broad OH peak.
Spectrum 3: 2-Cyanoacetamide
| Frequency | Assignment |
| 3200-3400 (2 peaks) | n(NH2, primary amine) |
| 2250 | n(C=N, nitrile) |
| 1700 | n(C=O, ketone) |
| Frequency | Assignment |
| 3020 | n(CH, sp2, aromatic) |
| 2850-2950 | n(CH, sp3, alkane) |
| 1700 | n(C=O, ketone) |
| 1600, 1500 | n(C=C, aromatic) |
| 800 | oop bending, para substitution |
| Frequency | Assignment |
| 2850-2980 | n(CH, sp3, alkane) |
| 1460 | d(CH2, CH3, bend) |
| Frequency | Assignment |
| 3200 (2 peaks) | n(NH2, primary amine) |
| 2850-2950 | n(CH, sp3, alkane) |
| 1600, br | d(NH2, bend) |
| 1450 | d(CH2, CH3, bend) |
| 1360 | n(C(CH3)2, doublet ) |
| 1020 | n(NC) |
| Frequency | Assignment |
| 3400, br | n(OH, alcohol/phenol) |
| 3020 | n(CH, sp2, aromatic) |
| 2850-2950 | n(CH, sp3, alkane) |
| 1600 | d(OH, bend; C=C, aromatic) |
| 1500 | n(C=C, aromatic) |
| Frequency | Assignment |
| 3050 | n(=CH, sp2, alkene) |
| 1760-1800 (2 peaks) | n(C=O, anhydride) |
| 1640 | n(C=C, alkene) |
| Frequency | Assignment |
| 3200 (1 peak) | n(NH, secondary amine) |
| 2850-2980 | n(CH, sp3, alkane) |
| 1455, 1363 | d(CH2,CH3, bend) |
| Frequency | Assignment |
| 3020 | n(=CH, sp2, alkene) |
| 2850-2980 | n(CH, sp3, alkane) |
| 1640 | n(C=C, alkene) |
| 1450, 1465 | d(CH2,CH3, bend) |
| 900 | oop bending (monosubst. alkene) |
General comments:
1. The average grade for the assignemnt is 35 points (out of 40). If you scored significantly less than 30 points, I would advise you to see your TA or the instructor to seek some help and get a better insight on IR spectroscopy.
2. One of the most common mistakes was not to analyze the v(C-H) region correctly to determine what type of compound (alkane, alkene, aromatic, or mixed) is present.
3. The v(OH) peaks for acids and alcohols look very different and can be easily identified by looking at them.
4. Carbonyl peaks can be shifted to lower wavenumbers when the carbonyl function is conjugated to a p-system e.g. double bond or aromatic ring.