draw the starting materials needed to make of the following acetal.

Explanation:

Step1: Identify the acetal carbon

The acetal carbon is the carbon atom bonded to two oxygen atoms within the ring.

Step2: Determine the carbonyl precursor

Cleave the two $C-O$ bonds at the acetal carbon; the carbon becomes a carbonyl ($C=O$). $$ (CH_{3}){2}C(OR){2} \rightarrow CH_{3}COCH_{3} $$

Step3: Determine the diol precursor

The remaining fragment containing the two oxygen atoms becomes a diol by adding hydrogens. $$ HO-CH_{2}-CH_{2}-CH_{2}-OH $$

Answer:

The starting materials are acetone ($CH_{3}COCH_{3}$) and 1,3-propanediol ($HOCH_{2}CH_{2}CH_{2}OH$).