Pages

IR of alkanes


C-H stretch: For saturated carbons, this always occurs under 3000, with the rare exception of cyclopropane due to its ring strain. It can go higher than 3000 in unsaturated carbons.

As a general rule, ring strain and s character increases the frequency of a vibration, moving the peak to the left.

CH2 bending: Occurs around 1465

CH3 bending; Occurs around 1375 

Long-chain bending: This is a rocking motion which occurs with four or more CH2 in an open chain. It is around 720

C-C stretch: This has many weak peaks, so it is not considered useful.

Below is the spectra of cyclohexane, notice how the CH3 bend and the long-chain bend disappear:


No comments:

Post a Comment