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Structural Group Analysis
Following this, the absorptivity per gram carbon in the standard group absorbing is derived in
the following manner:
a c = Ma b /12.01n
where
a c is the absorptivity (g/L cm −1 ) per gram carbon of the type absorbing
M is the gram molecular weight
n is the number of carbon atoms of the type absorbing per molecule
12.01 is the gram atomic weight of carbon
a b is the absorptivity derived earlier
By use of the a c term for specific types of carbon (1.50 at 1465 cm −1 for methyl; 3.60–4.00 at
2880 cm −1 for methylene), the number of carbon atoms of that type present in the sample may be
calculated.
Another infrared spectroscopic procedure that has been employed to gain insight into the carbon
distribution in petroleum residua and related materials involves determination of the molecular
extinction coefficient E for the band under investigation.
E = (l/cl) log (I o /I)
where
c is the molarity of the solution
l is the path length in centimeters
I o /I is determined directly from the infrared spectrum and is actually the ratio of the intensity of
the incident light I o to the intensity of the transmitted light I
The fraction of hydrogen atoms h a attached to aromatic carbons can be derived in the following
manner:
h a = H A /(H A + H S )
where
H A is the number of aromatic hydrogen atoms
H S is the number of saturated hydrogen atoms
h a = [E 3030 /(E 3030 + E 2920 )] k
E 3030 and E 2920 are the extinction coefficients of the 3030 and 2920 cm −1 absorption bands, respectively. Studies with standard alkylaromatic compounds and polymers indicated that there was good
agreement between the theoretical and observed hydrogen distribution when k was unity.
The proportion of carbon atoms in methyl groups to the total number of carbon atoms can be
determined in a similar manner. Thus,
C Me /C T = H/C × E 1380 / E 3030 + E 2920
where
C Me is methyl carbon
C T is the total carbon
H/C is the atomic hydrogen–carbon ratio determined from elemental analysis
E 1380 is the extinction coefficient of the band at 1380 cm −1
E 3030 and E 2920 are the extinction coefficients of the bands at 3030 and 2920 cm −1 , respectively
Structural Group Analysis
Following this, the absorptivity per gram carbon in the standard group absorbing is derived in
the following manner:
a c = Ma b /12.01n
where
a c is the absorptivity (g/L cm −1 ) per gram carbon of the type absorbing
M is the gram molecular weight
n is the number of carbon atoms of the type absorbing per molecule
12.01 is the gram atomic weight of carbon
a b is the absorptivity derived earlier
By use of the a c term for specific types of carbon (1.50 at 1465 cm −1 for methyl; 3.60–4.00 at
2880 cm −1 for methylene), the number of carbon atoms of that type present in the sample may be
calculated.
Another infrared spectroscopic procedure that has been employed to gain insight into the carbon
distribution in petroleum residua and related materials involves determination of the molecular
extinction coefficient E for the band under investigation.
E = (l/cl) log (I o /I)
where
c is the molarity of the solution
l is the path length in centimeters
I o /I is determined directly from the infrared spectrum and is actually the ratio of the intensity of
the incident light I o to the intensity of the transmitted light I
The fraction of hydrogen atoms h a attached to aromatic carbons can be derived in the following
manner:
h a = H A /(H A + H S )
where
H A is the number of aromatic hydrogen atoms
H S is the number of saturated hydrogen atoms
h a = [E 3030 /(E 3030 + E 2920 )] k
E 3030 and E 2920 are the extinction coefficients of the 3030 and 2920 cm −1 absorption bands, respectively. Studies with standard alkylaromatic compounds and polymers indicated that there was good
agreement between the theoretical and observed hydrogen distribution when k was unity.
The proportion of carbon atoms in methyl groups to the total number of carbon atoms can be
determined in a similar manner. Thus,
C Me /C T = H/C × E 1380 / E 3030 + E 2920
where
C Me is methyl carbon
C T is the total carbon
H/C is the atomic hydrogen–carbon ratio determined from elemental analysis
E 1380 is the extinction coefficient of the band at 1380 cm −1
E 3030 and E 2920 are the extinction coefficients of the bands at 3030 and 2920 cm −1 , respectively