16.3- INFRARED SPECTROSCOPY Flashcards
What is infrared spectroscopy often used by organic chemists to do?
to help them identify compounds
What is a pair of atoms joined by a chemical bond always doing?
always vibrating
How do stronger bonds vibrate?
faster (at higher frequency)
How do heavier atoms make the bond vibrate?
more slowly (at lower frequency)
What is the frequency of each bond like?
every bond has its own unique natural frequency that’s in IR region of EM radiation
What happens when you shine a beam of IR radiation (heat energy) through sample?
bonds in sample can absorb energy from radiation + vibrate more
What radiation can any particular bond only absorb?
any particular bonds can only absorb radiation that has same frequency as natural frequency of bond
As any particular bonds can only absorb radiation that has same frequency as natural frequency of bond, what is the radiation emitted by sample like? (infrared spectroscopy)
radiation that emerges from sample will be missing frequencies that correspond to bonds in sample
What happens in an infrared spectrometer: beam of IR radiation #1
beam of IR radiation containing spread of frequencies passed through sample
What happens in an infrared spectrometer: radiation that emerges #2
radiation that emerges is missing frequencies that correspond to types of bonds found in sample
What happens in an infrared spectrometer: instruments plot graph #3
instruments plot graph of intensity of radiation emerging from sample, called transmittance, against frequency of radiation
What happens in an infrared spectrometer: what is frequency expressed as #4
as wavenumber, measured in cm-1
What are the dips in the IR spectrum called?
peaks
What do the peaks on the IR spectrum represent?
particular bonds
What does a broad peak at about between 3230 + 3550cm-1 represent?
O-H bond in alcohols
