$"12.$ Determine the structures of the isomeric compounds A and $B,$ each of which has the formula $C_8{H}_7$BrO. The infrared spectrum for compound A has a strong absorption band at $1698c{m}^{-1},$ while compound $B$ has a strong band at $1688c{m}^{-1}.$ The ${?}^{1}H$ NMR spectrum for compound $A$ is shown, along with expansions for the region from $7\mathrm{.}7$ to $7\mathrm{.}2ppm.$ The ${?}^{1}H$ NMR spectrum of compound $B$ is also shown.

A$.$

$\frac{560}{745}$