The attack of the nucleophile always occurs at carbon rather than oxygen in a carbonyl compound; this is true when the reaction is kinetically controlled, and it is also true when the reaction is thermodynamically controlled. Explain.

A carbonyl compound consists of a carbon atom double-bonded to an oxygen atom (C=O). The carbon atom is electrophilic due to the difference in electronegativity between carbon and oxygen. Carbon, being less electronegative than oxygen, carries a partial positive charge (δ+), which makes it electron-deficient and attracts nucleophiles.

Kinetically controlled reactions are those in which the rate of the reaction is the determining factor. In these reactions, the product that forms the fastest is the major product. The partial positive charge on the carbonyl carbon atom is more accessible to the nucleophile compared to the oxygen atom because of its greater surface area and less sterically hindered. As a result, the nucleophilic attack on the carbon occurs faster than on the oxygen, making the product obtained from the attack on the carbon the major product under kinetic control.

Thermodynamically controlled reactions are those in which the stability of the products is the determining factor. The carbonyl compound can undergo two possible reactions: nucleophilic attack on the carbon atom, and nucleophilic attack on the oxygen atom. Since the carbonyl carbon is electrophilic (electron-deficient) and the nucleophile is electron-rich, the reaction between them leads to a more stable product compared to the reaction between the nucleophile and the oxygen atom. Oxygen, being more electronegative, has less affinity for forming additional bonds with the nucleophile. Hence, the product obtained from nucleophilic attack on the carbon is more stable and is the major product under thermodynamic control.

In summary, regardless of whether a reaction involving a carbonyl compound is kinetically or thermodynamically controlled, a nucleophile always attacks the carbon atom rather than the oxygen atom. The main reason for this is due to the electrophilic nature of the carbonyl carbon atom, its accessibility to the nucleophile, and the formation of a more stable product when the nucleophile attacks the carbon atom rather than the oxygen atom.