When treated with base, the following compound undergoes an intramolecular aldol reaction to give a product containing a ring (yield \(78 \%\) ).

Aldol condensation is a fundamental organic chemistry reaction, where two carbonyl compounds (often an aldehyde or ketone) combine to form a larger molecule that contains a beta-hydroxy carbonyl structure. The process begins with the formation of an enolate ion from one of the carbonyl reactants. This ion then attacks another carbonyl molecule in a nucleophilic attack, forming a new carbon-carbon bond.

Upon the creation of the beta-hydroxy carbonyl product, a subsequent dehydration step often occurs, especially under heating or under acidic conditions. This loss of water results in the formation of an alpha, beta-unsaturated carbonyl compound, which displays conjugation between the double bonds increasing the molecule's stability. The essential appeal of aldol condensation lies in its ability to efficiently build complex structures, including rings, and to introduce double bonds adjacent to carbonyl groups which are valuable features in synthetic chemistry.

The enolate ion is a negatively charged intermediate crucial in organic reactions such as aldol condensation. It forms when a base deprotonates an alpha hydrogen of a carbonyl compound. Carbonyl compounds typically are ketones or aldehydes with at least one hydrogen atom on their alpha-carbon, the carbon adjacent to the carbonyl carbon.

An important characteristic of enolate ions is their resonance stability. The negative charge can delocalize between the alpha-carbon and the oxygen of the carbonyl group, giving rise to resonance forms. This delocalization is not merely a theoretical concept; it has practical implications for the reactivity of enolate ions, making them good nucleophiles and capable of attacking electrophilic centers, such as another carbonyl carbon, leading to the formation of new carbon-carbon bonds. The stability, reactivity, and formation of enolate ions are foundational to understanding much of carbonyl chemistry.

In the context of organic chemistry, nucleophilic attack refers to the process where a nucleophile, an electron-rich species, donates an electron pair to an electrophile, an electron-deficient center. This forms a new chemical bond, typically resulting in the nucleophile becoming covalently attached to the electrophile.

Intramolecular aldol reactions exemplify nucleophilic attacks where the enolate ion formed from a carbonyl compound attacks the electrophilic carbon of another carbonyl group within the same molecule. The intramolecular nature of the attack can lead to the formation of five- or six-membered rings, which are generally favored due to their thermodynamic stability. A successful nucleophilic attack is a critical step in building more complex molecules, and understanding the factors that influence it, such as steric hindrance and electronic effects, is vital for mastering organic synthesis.

Carbonyl group chemistry is paramount in organic synthesis, encompassing reactions involving compounds that contain a carbon-oxygen double bond, like aldehydes and ketones along with more complex systems like carboxylic acids, esters, and amides. The carbonyl carbon atom is electrophilic due to its partial positive charge, a consequence of the oxygen's higher electronegativity.

One important aspect of carbonyl chemistry is the alpha-carbon reactivity. The alpha hydrogens on a carbonyl compound can be acidic and, as such, can be deprotonated to form enolate ions, which serve as nucleophiles in various reactions, including aldol condensation. The versatility of the carbonyl group also manifests in reactions such as nucleophilic substitutions, oxidations, reductions, and the formation of various other functional groups. Understanding the principles of carbonyl group reactivity unveils a vast array of synthetic possibilities that are critical for the production of many important molecules in pharmaceuticals, materials, and natural products.