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Concepts and reason

IR spectrum is an analysis of the interaction of molecule with infrared radiation. IR spectra help to identify the different functional groups present in a compound.

Fundamentals

Infrared spectroscopy:

Infrared bands appear at the certain absorption frequencies.

wave number (or)absorbance is v
v=IK
2πο γμ
where
u=reduced mass
c=speed of light
k=spring constnt of the bond

Reduced mass and spring constant of a bond changes according to the function group. Stronger bonds with lighter atoms are having higher frequency range. Different functional group gives absorption band at different range and intensity in IR. By knowing the absorption range, predict the functional group present in the given molecule. The table shown below gives the IR absorption of the common functional groups.

These groups absorb the IR radiation since their bonds are polar, which makes the bonds to vibrate at a particular wavenumber, and by using the wave numbers, different functional groups can be identified in the IR spectra.

Functional group

Range of absorption (cm)

Alkane(C-H)

2800-2900

Alcohol(O-H)

3400-3600

Alkene(C=C)

(C=C-H)

1640-1680

3020-3100

Alkyne(C=C)

(C=C-H)

2100-2250

3300

Nitrile(C=N)

2200-2250

Aromatics

1650-2000

Amines (N-H)

3300-335

Carbonyls(C=0)

Aldehyde(CHO)

Ketone (RCOR)

Ester (RCOOR)

Acid (RCOOH)

1720-1690

1750-1680

1750-1735

1780-1710

The given IR spectrum contains two bands.

Peak at 2900-2800cm
indicates the Alkyl bond and peak at 1500-1480cm
indicates the alkyl bond.

ОН
1-hexene-3-ol

Peaks at 3400cm-(0-H)
and another is at 1600cm*(C=C)
.

1-methyl cyclopentene

This compound shows peaks at3000cm*(C=C-H),
1650 cm* (C=C), 1425 cm-, and 1000 cm

ОН
3-hexanol

Peak near at 3600-3400 cm (O-H).

1,5-hexadiene

This compound contains three peaks. Peaks are given below: 3100cm, 3000 cm(C=C-H), and 1640 cm, 1000(C=C) and 900 cm (C-H bending).

cyclohexane

Three peaks are present in the cyclohexane at 2900-2800cm (C-H)and 1500-1480cm (C-C).

trans-4-octene

Trans -4-octene has two functional groups that is alkene(C=C)
at 1600cm
and (C=C-H)
at 3000cm

dipropyl ether

This compound shows peaks at 2850-2975 cm (Alkane), and 1100 cm (C-O-H).

Wrong options are 3- hexanol, 1-hexen-3-ol, dipropyl, 1-methylcylcopente, 1,5-hexadiene,and trans-4-octene.

2.6 2.8 3
4 4.5
wavelength, micrometers
5 5.5 6 7 8 9 10
11 12 13 14 1516
3.5
m
percent transmittance
alkane(C-C) 1500cm
| al

Cyclohexane is correct option.

In given IR spectrum contains two bands.

Peak at 2900-2800cm-1 indicates the Alkyl bond and peak at 1100 cm-1 indicates the C-O-C
bond.

Three peaks are present in the cyclohexane at

This compound shows peaks at

.

Peaks at and another peak is at .

This compound contains three peaks. Peaks are given below:

Peak near at

Trans -4-octene has two functional groups that is alkeneat and at

This compound shows peaks at

Wrong options are cyclohexane, 1-hexen-3-ol, 1,5-hexadiene, 3- hexanol, trans-4-octene, and 1-methylcylcopente.

2.6 2.8 3
3.5
4 4.5
wavelength, micrometers
5 5.5 6 7 8 9 10
11 12 13 141516
mm
alkane(C-O) 1100cm
alkane(C-H) 2900cm-1
3800

Dipropyl ether is the correct option.

The given IR spectrum contains broad peak at which indicates the group 3080cm
indicates the stretch of , and indicates the stretch.

This compound shows peaks at

Three peaks are present in the cyclohexane at

This compound contains three peaks. Peaks are given below:

Trans -4-octene has two functional groups that is alkeneat and at

Peak near at

Peaks at and another peak is at .

This compound shows peaks at

Wrong options are dipropyl ether, cyclohexane, 1,5-hexadiene, trans-4-octene, 3- hexanol, 1-hexen-3-ol, and 1-methylcylcopente.

1-hexan-3-ol is the correct option.

Ans:

1-hexen-3-ol
1-methylcyclopentene
3-hexanol
1,5-hexadiene
cyclohexane
trans-4-octene
dipropyl ether

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Which compound matches the IR spectrum? 1-hexen-3-ol 1-methylcyclopentene 3-hexanol 1.5-hoxadiene cylohexane trans-4-octene dipropyl ether Which compound...
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