how could you use infrared spectroscopy to detect the presence of ethanol in an oxygenated fuel?
I think it is either a C-O stretch or
-OH stretch, not sure which one? And I know there is more, but I don't know what to say. Please Help.
Infrared spectroscopy is termed a “chemical fingerprint.” It allows one to determine the presence of certain compounds in a sample by determining possible peak assignments through comparison of experimental and literature frequencies. Ethanol would result in an H-bonded
–OH stretch (3600-3100 cm-1) and a C-O stretch (1300-1000 cm-1).
Correct?
Oxygenated fuel is fuel that has an added material to increase the oxygen as the fuel (gasoline) burns. In the U. S., that was MTBE until it was outlawed and ethanol has taken the place of MTBE. So if you define oxygenated fuel as a hydrocarbon to which ethanol has been added, then the OH stretching around 3400 cm^-1 would be the one to use. If the fuel is dry (no water), then ethanol is the only absorption in that range (the C-H is close but usually doesn't interfere). You might want to look at the OH bending also.
Here is a table that may be useful. I talk about oxygenated fuel in terms of additives to gasoline but your question states oxygenated FUELS which could be anything for a fuel. If the fuel contains something besides hydrocarbons, the problem is more complicated.
http://www.chem.ucla.edu/~webspectra/irtable.html
By the way, aromatic hydrocarbons and alkenyl C-H frequencies are in the same range as the OH (which is broad).
Thanks
To use infrared spectroscopy to detect the presence of ethanol in an oxygenated fuel, you would need to look for specific absorption bands in the infrared spectrum that are characteristic of ethanol. Infrared spectroscopy relies on the selective absorption of infrared light by different chemical bonds, providing information about the types of functional groups present in a compound.
In the case of ethanol, you are correct that both the C-O and O-H functional groups will contribute to the infrared spectrum. The C-O stretch, which corresponds to the stretching vibration of the carbon-oxygen bond, typically occurs in the range of 1000-1300 cm^-1. The O-H stretch, which corresponds to the stretching vibration of the hydroxyl group, typically occurs in the range of 3200-3600 cm^-1.
In addition to these main absorption bands, there are usually other characteristic peaks that can aid in the identification of ethanol. For example, the C-H stretching vibrations of the methyl (CH3) and methylene (CH2) groups can be observed around 2800-3000 cm^-1.
To detect the presence of ethanol in an oxygenated fuel using infrared spectroscopy, you would need to obtain the infrared spectrum of the fuel sample and analyze it for the presence of these specific absorption bands. Comparing the obtained spectrum with reference spectra of known compounds can help confirm the identity of ethanol in the sample.
It's important to note that the specific absorption bands mentioned here are general ranges and can vary slightly depending on factors such as sample preparation, instrument calibration, and the presence of other functional groups in the fuel. Therefore, it is always advisable to consult a reference database and consider supplementary analytical techniques to validate the identification of ethanol in an oxygenated fuel.