$\underset{(1)}{\mathop{C{{H}_{3}}C{{H}_{2}}CHO}}\,$
$\underset{(2)}{\mathop{\begin{matrix} O \\ || \\ C{{H}_{3}}-C-C{{H}_{3}} \\ \end{matrix}}}\,$
$\underset{(3)}{\mathop{C{{H}_{3}}-CH=CH-OH}}\,$