3. The IR and mass spectra below were measured on a compound (A) containing 5 carbons. Assign the indicated bands in the IR (identify the bonds responsible by writing "sp³ C-H," "C-N," etc).
i) (2 points) The 2979 cm⁻¹ band is a ______ stretch.
ii) (2 points) The 1716 cm⁻¹ band is a ______ stretch.
b) (3 points) Propose a molecular formula for compound A, taking care that it is consistent with the
information above (incl. the IR spectrum) and with the mass spectrum shown here.
c) (3 points) Propose a structure for the base peak ion at m/e 57.
m/e intensity
27.0 12.4
29.0 59.4
57.0 100.0
86.0 21.2