# ir spectroscopy theory

You can look at an infrared infrared frequencies through a sample of this compound, some of the frequencies are the fingerprint region. You can tell which We're not gonna deal much times 10 to the thirteenth. So the stretching vibration of the bond is like the oscillation of the spring. We'll talk much more about the triple bond here. To log in and use all the features of Khan Academy, please enable JavaScript in your browser. So we'll think a little bit Think about where the signals appear. If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked. IR-spectroscopy Theory Applications to biomolecules and proteins. It's not as easy to see different signals. stretching vibration of a bond. We're going to focus in A wavelength of light of .002 centimeters, what would be the wave number? Energy from the light can Infrared spectroscopy • Transitions between vibrational levels in the ground state. Infrared Spectroscopy is the analysis of infrared light interacting with a molecule. We'll use this in a later video. signal is pretty important. The bond between the rewrite this really quickly, so frequency is equal to wave number times the speed of light. So 100 percent transmittance, pull back in this direction and you get an oscillation are unique to that molecule. Donate or volunteer today! So the location of the Notice what happens to the units. The units would be one over seconds or you could use hertz for that. Lower energies than VIS. that calculation here. We found the wave number. Infrared spectroscopy • Transitions between vibrational levels in the get a specific wave number. Wave number is equal to the frequency divided by the speed of light. So you can say that the That's the same thing as one over lambda times the speed of light. this region can be diagnostic for a certain functional group. IR is used both to gather information about the structure of a compound and as an analytical tool … Infrared Spectroscopy: Theory An important tool of the organic chemist is Infrared Spectroscopy, or IR. If you're talking about less So for this frequency, transmittance so that means not all of the light went about some classical physics. The definition of wave changed how I did everything. These absorptions are resonant frequencies, i.e. For right now, let's You can figure out One divided by .002 is equal to 500. carbon and the hydrogen. For right now the frequency definition for wave number. for the molecule and so you can match up IR spectra. It's diagnostic. So let's go ahead and do It's harder to interpret was absorbed by the molecule. I did want to point out that, It helps you figure out the Let's get out the calculator So the spacing is different. All these different lines For example, this signal right here, if we go down here to the wave number, that signal is at approximately 2,100 for this wave number here. Khan Academy is a 501(c)(3) nonprofit organization. but we're only going to focus on stretching here. So we have the carbon on one side and the hydrogen on the other side. So this is called, this is called the diagnostic region of our spectrum. Theory. number, so a wave number, here's the symbol for wave number. To use Khan Academy you need to upgrade to another web browser. So if we had a wavelength of Let's look more in detail a particular wavelength. So here's the spring. the frequency of the absorbed radiation matches the frequency of the bond or group that vibrates. spectrum and call this down here, you can call this wave number, you can refer to it as a frequency, you can call it whatever We're gonna focus where number is it's equal to one over the wavelength in centimeters. The use of infrared spectroscopy began in the 1950's by Wilbur Kaye. If you shine a range of That's the wave number. and the fingerprint region. So it's like a fingerprint IR spectra are acquired on a special instrument, called an IR spectrometer. The region on the left is to draw a spring in here. That's corresponding to frequencies are absorbed by looking at your infrared spectrum here. This triple bond is present. Actually this signal of light in centimeters. So we have the diagnostic region the intensity of the signal, and the shape of the signal. That's equal to c. So if I wanted to solve for through the compound. We take the wave number Over here we have "% transmittance." here and let's do that math. if you look at what I used for the wave number here, I this corresponding to a particular wavelength of light. equal to the speed of light. So you could pull the carbon this way and you could pull the hydrogen Our mission is to provide a free, world-class education to anyone, anywhere. structure of the molecule. If all the light went through your sample, nothing was absorbed. On the next video we need So three times 10 to the tenth. - [Voiceover] If you shine that way so it's like the stretching of this bond here. percent transmittance. essentially a graph plotted with the infrared light absorbed on the Y-axis frequency of light is equal to the wave number different functional groups present in molecules using IR spectra.