Question

Determine the molecular formula (not the structure!) for a compound with the following spectral data:

a. The IR spectrum shows peaks around 2900 and 1700 cm^-1(only 1 functional group)

b. The mass spectrum has a M⁺ at 58 m/z and a major fragment at 43 m/z (you may or may not find the fragment ion useful).

Answer 1

M+ is given at 58 m/z. By considering rule of 13 (C+H = 12+1 = 13), hydrocarbon formulla will be C₄H₁₀.

From IR data it is clear that there is only one functional group.

IR peak at 1700 cm-1 suggests a carbonyl stretch, means an O-atom.

No other data for other functional group is given.

At 2900 cm-1 peak corresponds to (sp³) C-H stretch.

So, now formula would be, after introducing an O - atom = C₃H₆O.

(Additional info: IR data and mass fragmentation suggests that it should be 2-propanone.)