Spectrum 1: Butyric anhydride (R2, C3)

Frequency Assignment
2880-2970 n(CH, sp3)
1750, 1819 n(C=O, anhydride)
1461, 1383 d (CH2, CH3, bend)
1031, 1039 n(C-O, anhydride)

Spectrum 2: p-Toluic acid (R3, C2)

Frequency Assignment
2500-3500 n(OH, acid)
1680 n(C=O, conjugated)
1492, 1603 n(C=C, aromatic)
1420 d(CH3, bend)
1287 n(C-O, acid)
767 oop, parasubst. arene

Spectrum 3: 3,4-Xylidine (R2, C1)

Frequency Assignment
3471, 3389 n(NH2, prim. amine)
3011 n(CH, sp2)
2862-2970 n(CH, sp3)
1628 d (NH2, scissoring)
1510, 1628 n(C=C, aromatic)
1375, 1453 d (CH3, bend)

Spectrum 4: p-Diethynylbenzene (R5, C4)

Frequency Assignment
3263 n(CH, sp)
2854-2956 n(CH, sp3, nujol)
2106 n(C=C)
1509, 1620 n(C=C, aromatic)
836 oop, para-disubst. arene

Spectrum 5: 3-Nitroxylene (R5, C3)

Frequency Assignment
3031 n(CH, sp2)
2873-2979 n(CH, sp3)
1530, 1612 n(C=C, aromatic)
1354, 1530 n(NO2)
1388, 1456 d (CH3, bend)

Spectrum 6: 4-Chromanol (R4, C4)

Frequency Assignment
3360 n(OH, alcohol)
3041, 3074 n(CH, sp2)
2896-2958 n(CH, sp3)
1488, 1585 n(C=C, aromatic)
1376, 1456 d (CH2, bend)
1063, 1223 n(C-O, ether)
755 oop, ortho-disubst. arene

Spectrum 7: Ethylbenzoate (R4, C3)

Frequency Assignment
3035, 3091 n(CH, sp2)
2874, 2983 n(CH, sp3)
1718 n(C=O, ester)
1492, 1603 n(C=C, aromatic)
1368, 1452 d(CH2, CH3, bend)
1108, 1276 n(C-O, ester)
688, 711 oop, mono-subst. arene

Spectrum 8: N-Methylbenzylamine (R2, C4)

Frequency Assignment
3308 n(NH, secondary amine)
3003-3107 n(CH, sp2)
2844-2969 n(CH, sp3)
1496, 1605 n(C=C, aromatic)
1356, 1454 d(CH2, CH3, bend)
698, 736 oop, mono-subst. arene

Spectrum 9: Tetralin (R3, C1)

Frequency Assignment
3019-3102 n(CH, sp2)
2841-2951 n(CH, sp3)
1496, 1602 n(C=C, aromatic)
1354, 1459 d(CH3, CH2, bend)

Spectrum 10: o-Ethoxybenzaldehyde (R3, C3)

Frequency Assignment
3042-3077 n(CH, sp2)
2938 n(CH, sp3)
2760, 2861 n(CHO)
1690

n(C=O, conj. aldehyde)
1488, 1600 n(C=C, aromatic)
1368, 1460 d(CH3, CH2, bend)
1042, 1243 n(C-O, ether)
759 oop, ortho-subst. arene

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 33 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.