Question

Bromination of 3 -methyl-2-butanone yielded two compounds, each having the molecular formula $\mathrm{C}_{5} \mathrm{H}_{9} \mathrm{BrO}$ in a $95: 5$ ratio. The ${ }^{1} \mathrm{H}$ NMR spectrum of the major isomer $\mathrm{A}$ was characterized by a doublet at $\delta 1.2$ (six protons), a septet at $\delta 3.0$ (one proton), and a singlet at $\delta 4.1$ (two protons). The ${ }^{1} \mathrm{H}$ NMR spectrum of the minor isomer $\mathrm{B}$ exhibited two singlets, one at $\delta 1.9$ and the other at $82.5$. The lower field singlet had half the area of the higher field one. Suggest reasonable structures for $\mathrm{A}$ and $\mathrm{B}$.

          Bromination of 3 -methyl-2-butanone yielded two compounds, each having the molecular formula $\mathrm{C}_{5} \mathrm{H}_{9} \mathrm{BrO}$ in a $95: 5$ ratio. The ${ }^{1} \mathrm{H}$ NMR spectrum of the major isomer $\mathrm{A}$ was characterized by a doublet at $\delta 1.2$ (six protons), a septet at $\delta 3.0$ (one proton), and a singlet at $\delta 4.1$ (two protons). The ${ }^{1} \mathrm{H}$ NMR spectrum of the minor isomer $\mathrm{B}$ exhibited two singlets, one at $\delta 1.9$ and the other at $82.5$. The lower field singlet had half the area of the higher field one. Suggest reasonable structures for $\mathrm{A}$ and $\mathrm{B}$.

Added by Kevin S.

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