Hello,

I was doing some AAMC practice problems and came across a couple questions where they talked about the disappearance or appearance of a stretch ? (Chem question pack - question 31) I was just wondering what they are referring to when they are speaking of a stretch? Would it be the bond itself (such as a single or double bond?) Thanks !

Hi,

Usually when you are looking at Infrared (IR) spectra, a stretch refers to the molecular motion of a bond, which can be anything from triple to double to single bonds.

For the MCAT, just recall that a stretch refers to the cm-1 value of a specific type of bond (most often carbonyl as it's pretty diagnostic).

Because IR is looking at molecular motion of certain bonds, you'll often hear terms like stetch and bend as it is describing the motion of the bonds that IR is observing.

This is a bit more complicated than the MCAT tests for.

In short for the purposes of the MCAT: Stretch/Bend refers to what cm-1 in an IR spectrum you would expect.