Spectrum 1: trans 2-Butanal (R3, C2)

Frequency Assignment
3362 C=O overtone
3003-3031 n(CH, sp2)
2918-2976 n(CH, sp3)
2733, 2814

n(CHO, aldehyde)
1691

n(C=O, conj. aldehyde)
1642 n(C=C, alkene)
1376, 1444 d(CH3, bend)
970 oop, trans alkene

Spectrum 2: 3-Phenyl butyric acid (R4, C1)

Frequency Assignment
2500-3500 n(OH, carboxylic acid)
1707 n(C=O, carboxylic acid, sat.)
1495, 1603 n(C=C, aromatic)
1367, 1454 d(CH3, bend)
1281 n(C-O, acid)
700, 758 oop, mono subst.

Spectrum 3: sec. Butylamine (R2, C3)

Frequency Assignment
3286, 3362 n(NH2, prim. amine)
2878-2962 n(CH, sp3)
1603 d(NH2, scissoring)
1377, 1454 d(CH2, CH3, bend)

Spectrum 4: 3-Hexanone (R5, C2)

Frequency Assignment
3414 C=O-overtone
2878-2965 n(CH, sp3)
1715 n(C=O, ketone)
1377, 1460 d(CH2, CH3, bend)

Spectrum 5: 3-Chloropropyne (R5, C1)

Frequency Assignment
3299 n(CH, sp, alkyne)
2958, 2997 n(CH, sp3)
2132 n(C=C, alkyne)
1431 d(CH2, bend)
710 n(CCl)

Spectrum 6: Limonene (R1, C2)

Frequency Assignment
3012-3084 n(CH, sp2)
2836-2966 n(CH, sp3)
1645

n(C=C, alkene)
1377, 1453

d(CH2, CH3, bend)
888 oop, mono subst. alkene
797 oop, tri subst. alkene

Spectrum 7: Angelic acid isobutyl ester (R1, C1)

Frequency Assignment
3010 n(CH, sp2)
2880-2963 n(CH, sp3)
1718 n(C=O, ester, conj.)
1651 n(C=C, alkene)
1383, 1471 d(CH3, bend)
1084, 1233 n(C-O-C, ester)

Spectrum 8: Diphenylamine (R4, C4)

Frequency Assignment
3434 n(NH, sec. amine)
3020-3092 n(CH, sp2)
1509, 1594 n(C=C, aromatic)
690 oop, mono subst.

Spectrum 9: Nitrocyclopentane (R3, C3)

Frequency Assignment
2878-2966 n(CH, sp3)
1373, 1548 n(NO2)
1453 d(CH2, bend)

Spectrum 10: Docecamide (R5, C3)

Frequency Assignment
3196, 3360 n(NH2, prim. amide)
2850-2955 n(CH, sp3)
1660 n(C=O, amide)
1633 d(NH2, scissoring)
1379, 1457

d(CH2, CH3, bend)

Note: The designation behind the name is the row and column number the molecule is located in the table.


General comments:

1. The average grade for the assignment is 36 points (out of 40). If you scored around or less than 30 points, I would advise you to see your TA or the instructor to seek some help.

2. One of the most common mistakes was not to analyze the n(C-H) region correctly to determine what type of compound (alkane, alkene, aromatic, or mixed) is present. Just writing "sp3" or "C-H" is not sufficient here.

3. The n(OH) peaks for acids and alcohols look very different and can be easily identified by looking at them (see reader). However, in some cases intramolecular hydrogen bonding broadens and shifts (to lower wavenumbers) the peak of an alcohol.

4. Carbonyl peaks can be shifted to lower wavenumbers when the carbonyl function is conjugated to another p-system e.g. double bond or aromatic ring.

5. Nitro groups show two intense peaks in the IR spectrum: one between 1300-1400 cm-1 for the symmetric stretching mode, the other one between 1500-1600 cm-1 for the asymmetric stretching mode.

6. The presence of two peaks in the carbonyl range (1630-1850 cm-1) indicates either the presence of an "anhydride type" of function or two different carbonyl functions.

7. Peaks due to amine, alkyne or alcohol functions are very different in appearance. Alkyne peaks (CH stretch) are very sharp and fairly intense due to an "isolated" motion. Amine peaks are usually a little broader and less intense. The presence of two peaks suggests a primary amine (NH2) while secondary amines show only one peak in this range. Alcohols (OH-stretch) usually show a rounded peak in this area.

8. If the spectrum shows a lot of peaks (independent from their size), the molecule has to have a lot of atoms and also cannot be very symmetric.