296
The Chemistry and Technology of Petroleum
Indeed, studies of the infrared spectra of a variety of compounds have demonstrated systematic correlation with structure. Thus it is not surprising that attempts have been made to estimate the structural
entities present in petroleum and other carbonaceous materials by means of infrared spectroscopy.
When properly prepared and scanned with suitable instruments, the infrared spectra of petroleum
fractions show a number of well-defined bands (Table 11.2; Rao, 1961). For the purposes of structural
group analysis, however, the bands at 1380, 1465, 2880, and 2920 cm −1 are usually employed. This
allows an estimation of the number of methyl and methylene groups present in the samples.
Thus, initially, the absorptivity, in grams per liter per centimeter, is calculated as
a b = A b /cl
where
a b is the absorptivity (g/L cm −1 ) at the wavelength b
A b is the absorbance of the solution at wavelength b
c is the concentration of the solution (g/L)
l is the cell thickness in centimeters
TABLE 11.2
Infrared Absorption Frequencies
Bond
Compound Type
Frequency Range, cm −1 (Wave Number)
O–H
Monomeric alcohols and phenols
3640–3160 (s, br) stretch
O–H
Hydrogen-bonded alcohols and phenols
3600–3200 (b) stretch
N–H
Amines, amides
3560–3320 (m) stretch; nonhydrogen bonded
N–H
Amines
3400–3100 (m) stretch; hydrogen bonded
C–H
Alkynes
3333–3267 (s) stretch
C–H
Aromatic rings
3100–3000 (m) stretch
C–H
Alkenes
3080–3020 (m) stretch
O–H
Carboxylic acids
3000–2500 (b) stretch
C–H
Alkanes
2960–2850 (s) stretch
C≡N
Nitriles
2260–2220 (v) stretch
C≡C
Alkynes
2260–2100 (w, sh) stretch
C–H
Phenyl ring substitution
2000–1600 (w)
C=O
Aldehydes, ketones, carboxylic acids, esters
1760–1670 (s) stretch
C=C
Alkenes
1680–1640 (m, w) stretch
NO 2
Nitro-compounds
1660–1500 (s) asymmetrical stretch
N–H
Amines
1650–1580 (m) bend
C=C
Aromatic rings
1600, 1500 (w) stretch
C–H
Alkanes
1470–1350 (v) scissoring and bending
NO 2
Nitro-compounds
1390–1260 (s) symmetrical stretch
C–H
CH 3 deformation
1380 (m or w, can be a doublet) -isopropyl, t-butyl
C–N
Amines
1340–1020 (m) stretch
C–O
Alcohols, ethers, carboxylic acids, esters
1260–1000 (s) stretch
C–H
Alkenes
1000–675 (s) bend
C–H
Phenyl ring substitution
870–675 (s) bend
C–H
Alkynes
700–610 (b) bend
C–Cl
Chloro-compounds
600–800 (m, w)
C–Br
Bromo-compounds
500–600 (m, w)
C–I
Iodo-compounds
500 (n, w)
v, variable; m, medium; s, strong; br, broad; w, weak; wave number = 1/wavelength.
The Chemistry and Technology of Petroleum
Indeed, studies of the infrared spectra of a variety of compounds have demonstrated systematic correlation with structure. Thus it is not surprising that attempts have been made to estimate the structural
entities present in petroleum and other carbonaceous materials by means of infrared spectroscopy.
When properly prepared and scanned with suitable instruments, the infrared spectra of petroleum
fractions show a number of well-defined bands (Table 11.2; Rao, 1961). For the purposes of structural
group analysis, however, the bands at 1380, 1465, 2880, and 2920 cm −1 are usually employed. This
allows an estimation of the number of methyl and methylene groups present in the samples.
Thus, initially, the absorptivity, in grams per liter per centimeter, is calculated as
a b = A b /cl
where
a b is the absorptivity (g/L cm −1 ) at the wavelength b
A b is the absorbance of the solution at wavelength b
c is the concentration of the solution (g/L)
l is the cell thickness in centimeters
TABLE 11.2
Infrared Absorption Frequencies
Bond
Compound Type
Frequency Range, cm −1 (Wave Number)
O–H
Monomeric alcohols and phenols
3640–3160 (s, br) stretch
O–H
Hydrogen-bonded alcohols and phenols
3600–3200 (b) stretch
N–H
Amines, amides
3560–3320 (m) stretch; nonhydrogen bonded
N–H
Amines
3400–3100 (m) stretch; hydrogen bonded
C–H
Alkynes
3333–3267 (s) stretch
C–H
Aromatic rings
3100–3000 (m) stretch
C–H
Alkenes
3080–3020 (m) stretch
O–H
Carboxylic acids
3000–2500 (b) stretch
C–H
Alkanes
2960–2850 (s) stretch
C≡N
Nitriles
2260–2220 (v) stretch
C≡C
Alkynes
2260–2100 (w, sh) stretch
C–H
Phenyl ring substitution
2000–1600 (w)
C=O
Aldehydes, ketones, carboxylic acids, esters
1760–1670 (s) stretch
C=C
Alkenes
1680–1640 (m, w) stretch
NO 2
Nitro-compounds
1660–1500 (s) asymmetrical stretch
N–H
Amines
1650–1580 (m) bend
C=C
Aromatic rings
1600, 1500 (w) stretch
C–H
Alkanes
1470–1350 (v) scissoring and bending
NO 2
Nitro-compounds
1390–1260 (s) symmetrical stretch
C–H
CH 3 deformation
1380 (m or w, can be a doublet) -isopropyl, t-butyl
C–N
Amines
1340–1020 (m) stretch
C–O
Alcohols, ethers, carboxylic acids, esters
1260–1000 (s) stretch
C–H
Alkenes
1000–675 (s) bend
C–H
Phenyl ring substitution
870–675 (s) bend
C–H
Alkynes
700–610 (b) bend
C–Cl
Chloro-compounds
600–800 (m, w)
C–Br
Bromo-compounds
500–600 (m, w)
C–I
Iodo-compounds
500 (n, w)
v, variable; m, medium; s, strong; br, broad; w, weak; wave number = 1/wavelength.