Spectrum 1: trans,trans-2,4-hexadienoic acid (R4, C2)

Frequency Assignment
2500-3500 n(OH, carboxylic acid)
1694

n(C=O, acid)
1613, 1638

n(C=C, alkene)
1377

d(CH3, bend)
1266

n(COH, acid)
998

oop, trans alkene

Spectrum 2: 1,4-Cyclohexadiene (R2, C4)

Frequency Assignment
3028, 3094 n(CH, sp2)
2824-2993

n(CH, sp3)
1640

n(C=C, alkene)
1430

d(CH2, bend)

Note: This compound is NOT aromatic!!

Spectrum 3: Glutaronitrile (R2, C1)

Frequency Assignment
2866-2966 n(CH, sp3)
2252

n(C≡N)

Spectrum 4: 2-Isopropyl-6-methylaniline (R3, C3)

Frequency Assignment
3395, 3478 n(NH2, prim. amine)
3037-3078

n(CH, sp2)
2870-2963

n(CH, sp3)
1482, 1624

n(C=C, aromatic)+ d(NH2, bend)
1468

d(CH3, bend)
1364, 1383 "iso-propyl doublet"

Spectrum 5: Ethyl 2-oxo-1-cyclopentanecarboxylate (R1, C3)

Frequency Assignment
3466 C=O overtone
2886-2980

n(CH, sp3)
1755

n(C=O, ketone)
1725

n(C=O, ester)
1455

d(CH2, bend)
1006, 1192

n(COC, ester)

Spectrum 6: p-Nitroanisole (R2, C2)

Frequency Assignment
3083, 3119 n(CH, sp2)
2843-2977

n(CH, sp3)
1504, 1592

n(C=C, aromatic)
1338, 1504

n(NO2)
1112, 1267

n(COC, ether)
1440 d(CH2, CH3, bend)

Spectrum 7: Pyrocatechol (R5, C2)

Frequency Assignment
3326, 3461 n(OH, diol)
3053 n(CH, sp2)
1514, 1603

n(C=C, aromatic)
1256

n(COH, phenol)

Spectrum 8: N-Cyclohexylacetamide (R1, C2)

Frequency Assignment
3065 n(NH, amide)
2852-2933 n(CH, sp3)
1641

n(C=O, amide)
1551

amide II
1374, 1445

d(CH2, CH3, bend)

Spectrum 9: o-Bromobenzaldehyde (R3, C4)

Frequency Assignment
3021-3086 n(CH, sp2)
2760, 2847 n(CHO, aldehyde)
1699

n(C=O, conj. aldehyde)
1588

n(C=C, aromatic)
758

oop, ortho-subst. arene
632 n(C-Br, sp2)

Spectrum 10: 1-Hexyne (R1, C1)

Frequency Assignment
3311 n(CH, sp)
2876-2962 n(CH, sp3)
2120

n(C≡C, alkyne)
1380, 1457

d(CH2, CH3, bend)
630 d(C≡C-H)


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 ~32 points (out of 40). About 10% of the class did not turn in the assignment on time. :-( 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 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 e.g. 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. However, this pattern is not observed in example 5 due to the limited ability of movement of the CHPh in the center.

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.