An unknown compound gives the NMR, IR, and mass spectra shown next. Propose a structure, and show how it is consistent with the observed absorptions. Show fragmentations that account for the prominent ion at m/z69 and the smaller peak at m/z99.

Mass spectrometry is a technique that helps in the identification of the structure of a compound. This technique is highly favored over other techniques as it does not lead to interference with the sample. It takes into account the mass by charge ratio of the various fragments produced from the molecular ion fragmentation to identify the compound's correct structure.

In the IR spectrum, A strong carbonyl peak at 1720 cm^-1 in conjunction with the C-O peak at 1200 cm^-1 , suggests the presence of an ester. An alkene peak appears at 1660 cm^-1 .

In the HNMR spectrum, the typical ethyl pattern stands out. The 3 H triplet is seen at, and a 2 H quartet is observed at δ =1.25. The chemical shift of CH2 indicates that it is connected to the oxygen atom. The other groups are a 3 H doublet at δ =1.8 which is a CH3 situated next to one hydrogen. A 1 H doublet is seen at δ =5.8, vinyl hydrogen with one neighboring hydrogen and 1 hydrogen multiplet is seen at δ =6.9. Another vinyl hydrogen with several neighbors is also seen. The far downfield chemical shift indicates that it is beta to the carbonyl. The large coupling constant in the doublet at δ =5.8 indicates that two vinyl hydrogens are trans.

Possible functional groups in the compound

The possible way to assemble this piece can be given as:

Possible structure of the compound

In the CNMR spectrum, a C=O of the ester is seen at δ =166, two vinyl carbons at δ =144 (beta to C=O) and δ =123 (alpha to C=O); the CH2-O of the ester at δ =60. The two methyls are seen at δ =18 and δ =14.

In the mass spectrum, this structure has a mass of 114, which is consistent with the molecular ion.

Fragmentation of the structure