Question

Consider the IR spectrum for cyclododecanol (below). There is a broad absorption at about 3250 cm^-1. What functional group is responsible for this absorption, and why is the absorption broad? Consider the IR spectrum for cyclododecanone (below). In the functional group region of the IR spectrum, specify the absorption associated with the carbon-oxygen double bond.

Answer 1

5. The peak present at 3250 cm-1 is belongs to O-H Stretching . The O-H-stretching modes from alcohols are mostly broad and very strong (3200-3650 cm^-1). O-H molecules more likely it is to form hydrogen bonds in more concentrated the solution. Since it is easier to stretch hydrogen bonds (because the oxygen pullsaway the electrons from hydrogen), minimum energy required to the peaks appear broad.

6. From previous alcohol was converted into corresponding ketone. Hence the peak appeared at 3250 cm-1 was dissappeared and new peak at ~ 1700cm-1 was found. This strong peak is belongs to C=O stretching . If any peak with very strong peak between 1660 and 1850 cm^-1, there is most likely a carbonyl function in the molecule. The exact peak position will reveal further what type of carbonyl function is present. The change in dipolemoment is significant making this as intense bond.