đáp án bài tập phổ hữu cơ IR NMR

Problem 1
C5H10O
MW 86
The band at 1716 indicates a carbonyl, probably a ketone. The bands at 3000-2850 indicate C-H alkane stretches.

Problem 1, NMR intrepreted


Problem2
C7H14O
MW 114
The band at 1718 indicates a carbonyl, probably a ketone. The bands at 3000-2850 indicate C-H alkane stretches.

Prob 2 NMR, interpreted


Problem 3
C4H10O
MW 74
The broad band at 3339 indicates O-H stretch, probably an alcohol. The bands at 3000-2850 indicate C-H alkane
stretches. The band at 1041 is C-O stretch, consistent with an alcohol.

Prob 3 NMR, interpreted


Problem 4
C6H14O
MW 102
The broad band at 3350 indicates O-H stretch, probably an alcohol. The bands at 3000-2850 indicate C-H alkane
stretches. The bands from 1320-1000 indicate C-O stretch, consistent with an alcohol.

Prob 4 NMR, interpreted

Note that the structure has a chiral center and the mixture is racemic. Methylene protons adjacent to a chiral center
may not be identical.


Problem 5
C4H8O2
MW 88
Prob 5, IR answer
The band at 1743 indicates a carbonyl, probably a saturated aliphatic ester. The bands at 3000-2850 indicate C-H
alkane stretches. The bands in the region 1320-1000 could be due to C-O stretch, consistent with an ester.

Prob 5 NMR, interpreted


Problem 6
C5H10O2
MW 102
Prob 6, IR answer
The band at 1740 indicates a carbonyl, probably a saturated aliphatic ester. The bands at 3000-2850 indicate C-H
alkane stretches. The bands in the region 1320-1000 could be due to C-O stretch, consistent with an ester.

Prob 6 NMR, interpreted


Problem 7
C5H10O
MW 86
Prob 7, IR answer

The band at 1728 indicates a carbonyl, probably an aldehyde; an aldehyde is also suggested by the band at 2719
which is likely the C-H stretch of the H-C=O group. The bands at 3000-2850 indicate C-H alkane stretches.

Prob 7 NMR, interpreted


Problem 8
C8H8O
MW 120
Prob 8, IR answer
The band at 1703 indicates a carbonyl; that the carbonyl is an aldehyde is suggested by the bands at 2828 and
2733 (C-H stretch of the H-C=O group). The bands at 3000-2850 indicate C-H alkane stretches. The band
(unmarked on the graph below) just to the left of 3000 indicates aromatic C-H stretch. Aromatics also show bands
in the regions 1600-1585 and 1500-1400 (C-C in-ring stretch), and 900-675 (C-H out-of-plane).

Prob 8 NMR, interpreted

Note: There are 4 aromatic protons (B, 7-8 ppm), indicating a disubstituted aromatic ring. You are not expected to
assign the individual peaks in the aromatic region to specific hydrogens on the aromatic ring. The aromatic
protons show a pattern characteristic of para substitution.


Problem 9
C9H10O2
MW 150
Prob 9, IR answer
The band at 1697 indicates an alpha, beta-unsaturated carbonyl; that the carbonyl is an aldehyde is suggested by
the bands at 2828 and 2739 (C-H stretch of the H-C=O group). The bands at 3000-2850 indicate C-H alkane
stretches. The band (unmarked on the graph below) just to the left of 3000 indicates aromatic C-H stretch.
Aromatics also show bands in the regions 1600-1585 and 1500-1400 (C-C in-ring stretch), and 900-675 (C-H outof-plane).

Prob 9 NMR, interpreted


Problem 10
C3H6O2
MW 74
Prob 10, IR answer
The band at 1716 indicates a carbonyl. The wide band from 3300-2500 is characteristic of the O-H stretch of
carboxylic acids. The bands at 3000-2850 indicate C-H alkane stretches. The bands in the region 1320-1000
indicate the C-O stretch of carboxylic acids.

Prob 10 NMR, interpreted


Problem 11
C11H14O2
MW 178
Prob 11, IR answer
The band at 1684 indicates a carbonyl. The wide band from 3300-2500 is characteristic of the O-H stretch of
carboxylic acids. The bands at 3000-2850 indicate C-H alkane stretches. The bands in the region 1320-1000
indicate the C-O stretch of carboxylic acids. The band (unmarked on the graph below) just to the left of 3000
indicates aromatic C-H stretch. Aromatics also show bands in the regions 1600-1585 and 1500-1400 (C-C in-ring
stretch), and 900-675 (C-H out-of-plane).

Prob 11 NMR, interpreted


Problem 12
C8H8O2

MW 136
Prob 12, IR answer
The band at 1684 indicates a carbonyl. The wide band from 3300-2500 is characteristic of the O-H stretch of
carboxylic acids. The bands at 3000-2850 indicate C-H alkane stretches. The bands in the region 1320-1000
indicate the C-O stretch of carboxylic acids. The band just to the left of 3000 (3065) indicates aromatic C-H
stretch. Aromatics also show bands in the regions 1600-1585 and 1500-1400 (C-C in-ring stretch), and 900-675
(C-H out-of-plane).

Prob 12 NMR, interpreted


Problem 13
C7H9N
MW 114
Prob 13, IR answer
The two bands at 3433 and 3354 indicate a secondary amine. The bands at 3000-2850 indicate C-H alkane
stretches. The band at 3034 indicates aromatic C-H stretch; aromatics also show bands in the regions 1600-1585
and 1500-1400 (C-C in-ring stretch), and 900-675 (C-H out-of-plane). C-N stretch of aromatic amines would
show up at 1335-1250 (there is a band in that region).

Prob 13 NMR, interpreted


Problem 14
C5H13N
MW 87
Prob 14, IR answer
The two bands at 3388 and 3292 indicate a secondary amine. The bands at 3000-2850 indicate C-H alkane
stretches.

Prob 14 NMR, interpreted


Problem 15
C8H14O
MW 126
Prob 15, IR answer
The band at 1718 indicates a carbonyl, probably a ketone. The bands at 3000-2850 indicate C-H alkane stretches.
Since the compound is an alkene, one would expect to see C=C stretch at 1680-1640; these weak bands are not
seen in this IR (according to Silverstein, "the C=C stretching mode of unconjugated alkenes usually shows
moderate to weka absorption at 1667-1640"). Since the compound is an alkene, C-H stretch should appear above
3000 (not seen: the absorption for this single hydrogen must be too weak).

Prob 15 NMR, interpreted


Problem 16
C4H9Br
MW 137
Prob 16, IR answer
The bands at 3000-2850 indicate C-H alkane stretches. The bands in the region 1300-1150 could indicate C-H
wag (-CH2Br) of an alkyl halide.

Prob 16 NMR, interpreted


Problem 17
C10H14O
MW 150
Prob 17, IR answer

The bands at 3000-2850 indicate C-H alkane stretches; the small (unmarked) band just to the left of 3000
indicates aromatic C-H stretch. Aromatics also show bands in the regions 1600-1585 and 1500-1400 (C-C in-ring
stretch), and 900-675 (C-H out-of-plane). The wide band in the region 3500-3200 indicates the O-H stretch of an
alcohol or phenol.

Prob 17 NMR, interpreted


Problem 18
C13H10O3
MW 214
Prob 18, IR answer
The band at 1682 indicates a carbonyl, probably an ester. The band at 3192 indicates C-H aromatic stretch;
aromatics also show bands in the regions 1600-1585 and 1500-1400 (C-C in-ring stretch), and 900-675 (C-H outof-plane). The wide band just to the left of the 3192 band indicates O-H stretch (alcohols and phenols).

Prob 18 NMR, interpreted

Note: the correct placement of the -OH on the ring and the arrangement of the ester may be beyond the scope of
your spectroscopy course. See this explanation.


Problem 18, structure


Problem 19
C8H14
MW 110
Prob 19, IR answer
The bands at 3000-2850 indicate C-H alkane stretches. There really aren't many other bands in the spectrum to
indicate functional groups. The compound is an alkyne; we would expect to see a carbon-carbon triple bond

stretch at 2260-2100, however, this is a weak band at best and often does not show up on IR.

Prob 19 NMR, interpreted

Note: The integral values for A, B, and C need to be multiplied by 2 to get a total of 14 protons in the molecule.
By convention, integral values on an nmr are reported as the lowest common multiple.


Problem 20
C9H13N
MW 135
Prob 20, IR answer
The bands at 3000-2850 indicate C-H alkane stretches. The band at 3028 indicates C-H aromatic stretch;
aromatics also show bands in the regions 1600-1585 and 1500-1400 (C-C in-ring stretch), and 900-675 (C-H outof-plane). The bands in the region 1250-1020 could be due to C-N stretch. The weak, broad banc at about 3500
could be amine N-H stretch or it could be a slight contamination of an impurity (water) in the sample.

Prob 20 NMR, interpreted


Problem 21
C9H10
MW 118
Prob 21, IR answer
The bands at 3000-2850 indicate C-H alkane stretches. The band at 3060 indicates C-H aromatic stretch;
aromatics also show bands in the regions 1600-1585 and 1500-1400 (C-C in-ring stretch), and 900-675 (C-H outof-plane).

Prob 21 NMR, interpreted