Understanding IR Spectrum: The Role of Transmittance and Absorption

[Samurai33]

http://x5.freeshare.us/view/?121fs535045.jpg
In the above diagram, what does the % of transmittance means?
I know the % of transmittance is the reverse of % absorption, but there are more C-H bond per molecule than C=O, why the intensity for C=O is higher(higher absorption)? I really have no clues!

 

[Samurai33]

can anyone explain??

 

[Blueshift5]

I can provide some insights into the concept of transmittance and absorption in the context of IR spectroscopy. IR spectroscopy is a powerful analytical technique used to identify and characterize chemical compounds based on their unique absorption patterns in the infrared region of the electromagnetic spectrum.

In the diagram provided, the % transmittance refers to the percentage of infrared radiation that passes through the sample without being absorbed. On the other hand, the % absorption refers to the percentage of infrared radiation that is absorbed by the sample. These two values are inversely related, meaning that as one increases, the other decreases.

The intensity of absorption for a particular bond or functional group in a molecule is dependent on several factors, including the type of bond, its strength, and the number of bonds present in the molecule. In the case of C-H bonds, they are typically weaker and less polar than C=O bonds. This means that they absorb less energy and have a lower intensity in the IR spectrum. On the other hand, C=O bonds are stronger and more polar, making them more likely to absorb energy and have a higher intensity in the IR spectrum.

It is also important to note that the intensity of absorption is not solely dependent on the number of bonds present in a molecule. Other factors such as the molecular structure and the orientation of the bonds can also affect the absorption intensity. Therefore, it is not surprising to see that the intensity of C=O absorption is higher than C-H absorption, even though there are more C-H bonds in a molecule.

In summary, the % transmittance and % absorption values in the IR spectrum provide valuable information about the chemical composition and structure of a sample. The intensity of absorption for a particular bond or functional group is influenced by various factors, and it is essential to consider all of these factors when analyzing IR spectra.