Using Figure 21.14 as a guide, identify regions of the IR spectrum in which you would expect to see characteristic functional group absorptions for each of the following compounds: (a) cyclopentanone, (b) methyl acetate, (c) methoxybenzene, (d) acetamide, (e) 1-aminohexane.
Using Figure 21.14 as a guide, identify regions of the IR spectrum in which you would expect to see characteristic functional group absorptions for each of the following compounds: (a) cyclopentanone, (b) methyl acetate, (c) methoxybenzene, (d) acetamide, (e) 1-aminohexane.
Using Figure 21.14 as a guide, identify regions of the IR spectrum in which you would expect to see characteristic functional group absorptions for each of the following compounds: (a) cyclopentanone, (b) methyl acetate, (c) methoxybenzene, (d) acetamide, (e) 1-aminohexane.
I need help to List the positions of ir absorption peaks of the various functional groups
Transcribed Image Text:FOLLOW-UP ASSIGNMENT
Using Figure 21.14 as a guide, identify regions of the IR spectrum in which
you would expect to see characteristic functional group absorptions for each
of the following compounds: (a) cyclopentanone, (b) methyl acetate,
(c) methoxybenzene, (d) acetamide, (e) 1-aminohexane.
Where to Begin
An efficient approach to interpreting an IR spectrum usually starts
with a survey of the 4000-1500 cm-1 functional group region and the
creation of an inventory of bond types present in the molecule. This
inventory allows you to get a good idea of which functional groups
are in the compound and which are not.
The functional group region can be subdivided into narrower
frequency regions that are characteristic of specific bond types.
Table 21.2 lists the positions of characteristic IR absorption peaks
of various functional groups. It is fairly accurate for strong (s) and
broad (br) peaks. However, because the intensities of IR absorptions
can vary a good deal, the use of Table 21.2 has limitations, particu-
larly for peaks listed as medium (m) and weak (w) intensity. Useful
IR corroborating peaks of the C-H out-of-plane bending vibrations
TABLE 21. 2
Characteristic infrared absorption peaks of functional groups
Vibration
Position (cm-)
Intensity“
Alkanes
C-H stretch
C-H bend
2990-2850
m to s
1480-1430 (CH,), 1395–1340 (CH,)
m to w
Alkenes
3100-3000
1680–1620 (nonconj.)», 1650–1600 (conj.)b
1000-665 (see Table 21.3 for detail)
=C-H stretch
C=C stretch
w to m
=C-H bend
Alkynes
=C-H stretch
C=C stretch
3310-3200
2250-2100
s to w
(Continued)
328
Part 5 • Spectrometric Methods
TABLE 21.2
(Continued)
Vibration
Position (cm-)
Intensity
Aromatic Compounds
C-H stretch
3100-3000
m to w
C=C stretch
1620-1440
m to w
Transcribed Image Text:328
Part 5 • Spectrometric Methods
TABLE 21.2
(Continued)
Vibration
Position (cm-)
Intensity
Aromatic Compounds
C-H stretch
C=C stretch
C-H bend
3100–3000
m to w
1620-1440
m to w
880–680 (see Table 21.3 for detail)
Alcohols
O-H stretch
C-O stretch
3650-3550 (non H-bonded), 3550–3200 (H-bonded)
1300-1000
s to m, br
Ethers
C-O stretch
1300-1000
Amines
N-H stretch
C-N stretch
3550-3250 (1° two peaks), (2° one peak)
1250–1025 (alkyl), 1350–1250 (aromatic)
br, m
Nitriles
C=N stretch
2280–2200
Isocyanates
N=C=O stretch
2275-2230
Aldehydes
=C-H stretch
C=O stretch
2900-2800 and 2800–2700, Fermi doublet
1740–1720 (non-conj.), 1715–1680 (conj.)
Ketones
C=O stretch
1725–1705 (non-conj.), 1700–1650 (conj.)
Esters
C=O stretch
1765–1735 (non-conj.), 1730–1715 (conj.)
1260–1230 (acetates), 1210–1160 (all others)
C(=O)-O stretch
Carboxylic Acids
O-H stretch
3200-2500
br, m to w
C=O stretch
C-O stretch
1725–1700 (non-conj.), 1715–1680 (conj.)
1300–1000
Amides
N-H stretch
C=O stretch
3500–3150 (1° two peaks), (2° one peak)
1700-1630
N-H bend
1570–1515 (primary), 1640–1550 (secondary)
Anhydrides
C=O stretch
1850–1800 and 1790–1740
C-O stretch
1300–1000
Acid Chlorides
C=O stretch
1815-1770
Imines
R,C=N-R stretch
1690-1630
m to s
Nitro Compounds
NO, stretch
1570-1490 and 1390-1300
Sulfoxides
S=O stretch
1070–1030
Sulfonates
S=O stretch
1375–1335 and 1195–1165
Phosphine Oxides
P=O stretch
1200-1130
Alkyl Halides
C-F stretch
C-CI stretch
1400-1000
785-540
a. s = strong; m = medium; w = weak; br = broad. b. non-conj. = non-conjugated; conj. = conjugated.
E n n
Definition Definition Group of atoms that shape the chemical characteristics of a molecule. The behavior of a functional group is uniform in undergoing comparable chemical reactions, regardless of the other constituents of the molecule. Functional groups aid in the classification and anticipation of reactivity of organic molecules.
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