Final answer:
In molecule A, the electrophilic site is the double bond between the two carbon atoms. In molecule B, the electrophilic site is the carbon atom connected to the carbonyl group. In molecule C, the electrophilic site is the carbon atom in the triple bond. In molecule D, the electrophilic site is the carbonyl carbon atom in the formyl group.
Step-by-step explanation:
In molecule A (CH3-CH=CH2), the electrophilic site is the double bond between the two carbon atoms. This is because the double bond has a positive charge on one of the carbon atoms, making it more attractive to electron-rich species, which are nucleophiles.
In molecule B (C6H5-CHO), the electrophilic site is the carbon atom connected to the carbonyl group (-CHO). The carbonyl group is a stronger electrophile due to the polarity of the C=O bond, with the more electronegative oxygen atom pulling electron density away from the carbon atom.
In molecule C (CH3-C≡N), the electrophilic site is the carbon atom in the triple bond. The triple bond consists of a sigma bond and two pi bonds, and the carbon atom in the triple bond has a partial positive charge in comparison to the more electronegative nitrogen atom.
In molecule D (HCOOH), the electrophilic site is the carbonyl carbon atom in the formyl group (-COOH). The electronegative oxygen atoms in the carboxyl group pull electron density away from the carbon atom, giving it a partial positive charge.