Propose mechanisms for the following reactions.
(a)

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Step 1: Identify the starting material and the product. The starting material is benzaldehyde (Ph-CHO), and the product is an acetal (Ph-CH(OCH3)2). This reaction involves the conversion of an aldehyde into an acetal in the presence of methanol (CH3OH) and an acid catalyst (H+).

Step 2: Protonation of the carbonyl oxygen. The acid catalyst (H+) protonates the oxygen atom of the aldehyde group, increasing the electrophilicity of the carbonyl carbon and making it more susceptible to nucleophilic attack.

Step 3: Nucleophilic attack by methanol. Methanol (CH3OH) acts as a nucleophile and attacks the carbonyl carbon, forming a tetrahedral intermediate. This intermediate has a hydroxyl group (-OH) and a methoxy group (-OCH3) attached to the carbon.

Step 4: Formation of the hemiacetal. The intermediate undergoes deprotonation at the hydroxyl group, resulting in the formation of a hemiacetal (Ph-CH(OH)(OCH3)).

Step 5: Conversion to acetal. The hydroxyl group of the hemiacetal is protonated again by the acid catalyst, making it a good leaving group. A second molecule of methanol attacks the carbon, replacing the hydroxyl group with another methoxy group (-OCH3), and the acetal (Ph-CH(OCH3)2) is formed after deprotonation.

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