A compound $\text{'}\mathrm{A}\text{'}$ of molecular formula ${\mathrm{C}}_4{\mathrm{H}}_{10}\mathrm{O}$ on treatment with Lucas' reagent at room temperature gives a compound $\text{'}\mathrm{B}\text{'}$. When the compound $\text{'}\mathrm{B}\text{'}$ is heated with alcoholic $\mathrm{KOH}$, it gives isobutene. The compound $\text{'}\mathrm{A}\text{'}$ and $\text{'}\mathrm{B}\text{'}$ respectively are