(A true story.) The chemistry department custodian was cleaning the organic lab when an unmarked bottle fell off a shelf and smashed on the floor, leaving a puddle of volatile liquid. The custodian began to wipe up the puddle, but he was overcome with burning in his eyes and a feeling of having an electric drill thrust up his nose. He left the room and called the fire department, who used breathing equipment to go in and clean up the chemical. Three students were asked to identify the chemical quickly so the custodian could be treated and the chemical could be handled properly. The students took IR and NMR spectra, which follow. The UV spectrum showed at 220 nm ( = 16,000) . The mass spectrometer was down, so no molecular weight was available. Determine the structure of this nasty compound, and show how your structure fits the spectra.
UV spectrum: The simplest conjugated carbonyl system is propenal. The transition of propenal occurs at of 210 nm (= 11,000). Alkyl substitution increases the value of by about 10 bnm per alkyl group. From this data, required compound is but-2-enal occurs at of 220 nm ().
IR spectrum: The strong peak at 1690 cm-1 must be a C=O group. The weak peak at 3000 cm-1 must be vinyl hydrogens
HNMR spectrum: The chemical shift value 9.5 shows an aldehyde group. The chemical value 6.0 shows vinyl proton is adjacent carbonyl group. The chemical value 6.0 shows vinyl proton is adjacent methyl group. The chemical shift value 2.0 shows a methyl group is adjacent to C=C
From the above data, the required compound is given below.