Question

In the given reaction,

\[\ce{2-Bromo-3, 3-dimethyl butane ->[C2H5OH][\underset{(Major product)}{'A'}]}\] Product A is ______.

Options

• 2-Hydroxy-3, 3-dimethyl butane

• 2-Ethoxy-2, 3-dimethyl butane

• 2-Ethoxy-3, 3-dimethyl butane

• 1-Ethoxy-3, 3-dimethyl butane

Answer 1

In the given reaction, 

\[\ce{2-Bromo-3, 3-dimethyl butane ->[C2H5OH][\underset{(Major product)}{'A'}]}\] Product A is 2-Ethoxy-2, 3-dimethyl butane.

Explanation:

After being treated with the first molecule of ethanol, 2-bromo-3, 3-dimethyl butane releases the bromide ion and creates a secondary carbocation. In order to transform the secondary carbocation into the more stable tertiary carbocation, the secondary carbocation goes through a 1, 2-methyl shift.
When the second ethanol molecule comes into contact with the tertiary carbocation, ethanol is added to the C atom of the tertiary carbocation. The resultant compound undergoes a rearrangement that primarily yields 2-Ethoxy-2, 3-dimethyl butane.

\[\begin{array}{cc}
\phantom{.......}\ce{CH3}\phantom{}\ce{BR}\phantom{.......................}\ce{CH3}\phantom{................}\\
\phantom{....}|\phantom{....}|\phantom{..........................}|\phantom{................}\\
\ce{CH3 - C - CH - CH3 ->[C2H5OH][- Br^⊖] CH3 - C - \overset{⊕}{C}H - CH - CH3}\\
|\phantom{..............................}|\phantom{............}\\
\phantom{...}\ce{\underset{2-Bromo-3, 3-dimethyl butane}{CH3}}\phantom{.............}
\ce{\underset{1, 2,-methyl shift}{CH3}}\phantom{................}\\
\phantom{...................}\downarrow\\
\ce{H}\phantom{............................................}\\
|\phantom{............................................}\\
\ce{^⊕ O - CH2 - CH3 <-[C2H5OH] CH3 - \overset{⊕}{C} - CH - CH3}\\
\phantom{..}|\phantom{...............................}|\phantom{.....}|\phantom{.........}\\
\phantom{...}\ce{CH3 - C - CH - CH3}\phantom{...........}\ce{CH3}\phantom{.}\ce{CH3}\phantom{........}\\
|\phantom{....}|\phantom{...........................}\\
\ce{CH3}\phantom{.}\ce{CH3}\phantom{.........................}\\
⇅\phantom{...............................}\\
\ce{O - CH2 - CH3}\phantom{..................}\\
|\phantom{................................}\\
\ce{^1CH3 - ^2C - ^3CH - ^4CH3}\phantom{..........................}\\
|\phantom{.....}|\phantom{...........................}\\
\ce{\underset{2 Ethoxy-2, 3-dimethyl butane}{\phantom{..}CH3 \phantom{.}CH3\phantom{.}}}\phantom{.........................}
\end{array}\]

Therefore, compound A is 2-Ethoxy-2, 3-dimethyl butane.