The mass spectrum of unknown compound A shows a molecular ion at m/z 116 and prominent peaks at m/z 87 and m/z 101. Its UV spectrum shows no maximum above 200 nm. The IR and NMR spectra of A follow. When A is washed with dilute aqueous acid, extracted into dichloromethane. and the solvent evaporated, it gives a product B. B shows a strong carbonyl signal at 1715 cm-1 in the IR spectrum and a weak maximum at 274 nm (ε = 16) in the UV spectrum. The mass spectrum of B shows a molecular ion of m/z 72. Determine the structures of A and B, and show the fragmentation to account for the peaks at m/z 87 and 101.

Transcribed Image Text:

wavelength (um) 5 2.5 100 7-8-9-10一一11-12-13 4 4.5 5-6 14 15 16 80 60 N Compound A 20 3500 3000 2000 1800 1600 1400 1200 000 800 wavenumber (cm 200 180 160 140 120 100 80 60 40 0 Compound A 10 6 0 δ (ppm)