The isomer of diethyl ether is

The major product in the following reaction sequence is:

$1^o, 2^o, 3^o$ alcohols are distinguished by

The solubility of anhydrous $AlCl_3$ and hydrous $AlCl_3$ in diethyl ether are $S_1$ and $S_2$ respectively. Then:

Esterification of the acid $P$ with the alcohol $Q$ will give:

$p-$Cresol reacts with chloroform in an alkaline medium to give compound $A$,which reacts with hydrogen cyanide to form compound $Y$. Hydrolysis of $Y$ gives a chiral carboxylic acid. Identify the structure of the carboxylic acid.