Solution
= Solution
The $1621\,\mathrm{cm^{-1}}$ absorption is predominantly the <carbon–carbon double-bond stretching vibration> of the electron-rich <vinyl ether>. <resonance donation> from an <oxygen> <lone pair> changes both its frequency and its <electric dipole moment> variation during stretching. There is no <carbonyl> in the assigned structure, consistent with the absence of a <carbon-13 NMR> signal in the usual <ketone> or <acyl chloride> region.