Spectrum 1: p-Diacetylbenzene (R1, C4)

Frequency Assignment
3366

n(OH, broad, water contamination)
3003-3094

n(CH, sp2)
2920-2990

n(CH, sp3)
1676

n(C=O, conj. ketone)
1504

n(C=C, aromatic)
1382, 1427

d(CH3, bend)
837

oop, parasubst. arene

Spectrum 2: a-Methylcinnamic acid (R2, C3)

Frequency Assignment
2400-3400

n(OH, carboxylic acid)
1670

n(C=O, conj. carboxylic acid)
1618

n(C=C, alkene)
1493, 1575

n(C=C, aromatic)
1366, 1449

d(CH3, bend)
1288

n(C-O, carboxylic acid)

Spectrum 3: Carvacrol (R3, C4)

Frequency Assignment
3100-3700

n(OH, phenol)
3023

n(CH, sp2)
2871-2961

n(CH, sp3)
1502, 1621

n(C=C, aromatic)
1383, 1450

d(CH3, bend)
1253

n(C-OH, phenol)

Spectrum 4: p-Nitrophenyl acetate (R3, C2)

Frequency Assignment
3086-3115

n(CH, sp2)
2890

n(CH, sp3)
1761

n(C=O, ester)
1488, 1592

n(C=C, aromatic)
1360, 1520

n(NO2)
1367, 1429

d(CH3, bend)
1042, 1193

n(COC, ester)
853

oop, parasubst. arene

Spectrum 5: p-Isobutylbenzaldehyde (R4, C3)

Frequency Assignment
3029-3087

n(CH, sp2)
2860-2968

n(CH, sp3)
2732, 2824

n(CHO, aldehyde)
1700

n(C=O, conj. aldehyde)
1488, 1606

n(C=C, aromatic)
1385, 1466

d(CH2, CH3, bend)
846

oop, parasubst. arene

Spectrum 6: N-Methyl-p-toluenesulfonamide (R2, C1)

Frequency Assignment
3273

n(NH, sec. amide)
3045-3065

n(CH, sp2)
2811-2979

n(CH, sp3)
1495, 1597

n(C=C, aromatic)
1380, 1454

d(CH3, bend)
1158, 1318

n(SO2)
823

oop, parasubst. arene

Spectrum 7: Valeronitrile (R5, C4)

Frequency Assignment
2877-2964

n(CH, sp3)
2247

n(C≡N)
1383, 1468

d(CH2, CH3, bend)

Spectrum 8: 2,5-Xylidine (R4, C1)

Frequency Assignment
3373, 3461

n(NH2, prim.amine)
3010, 3063

n(CH, sp2)
2868-2972

n(CH, sp3)
1627

d(NH2, bend)
1517, 1580

n(C=C, aromatic)
1379, 1453

d(CH3, bend)
798, 861

oop, 1,2,4-subst. arene

Spectrum 9: 3-Methyl-1,4-pentadiene (R1, C3)

Frequency Assignment
3001-3195

n(CH, sp2)
2870-2971

n(CH, sp3)
1636

n(C=C, alkene)
1370, 1456

d(CH3, bend)
914, 994

oop, monosubst. alkene

Spectrum 10: Dichloroacetamide (R5, C2)

Frequency Assignment
3162, 3332

n(NH2, prim.amide)
3002

n(CH, sp3)
1685

n(C=O, amide)
658, 801

n(CCl)


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. There is still some time to practice and do better in the final exam.

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) is present. Just writing "sp3" or "C-H" is not sufficient here.

3. The n(OH) peaks for carboxylic 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 i.e., double bond or aromatic ring.

5. 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. These peaks can vary grealy in terms of their relative intensities.

6. 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. There is also a difference between amine and amides in terms of width and intensity of the peaks.

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.

9. Amide and amine are not the same functionality! Many students mislabeled the peaks in these peaks.

10. Finally, a significant number of assignments were rather sloppy done: poor labeling, structures that are not a choice, benzene rings without the double bonds, five-bonded carbon or nitrogen atoms, etc.