Question

Choose the incorrect statement(s): (A) Carbonyl carbon is an electrophilic or Lewis acid centre (B) Carbonyl compounds have substantial dipole moments and are less polar than ether (C) Carbonyl oxygen is an nucleophilic or Lewis base centre (D) Carbonyl carbon and three atoms attached to it lie in the same plane and \(p\)-electron cloud is \(20^{60^{4}}\) and below the plane

Short answer

The incorrect statements are (B), (C), and (D). Statement (B) is incorrect because carbonyl compounds are generally more polar than ethers. Statement (C) is incorrect because carbonyl oxygen is considered an electrophilic or Lewis acid center, not a nucleophilic or Lewis base center. Statement (D) is incorrect due to the angle notation; it should be written as 120° instead of \(20^{60^{4}}\).

Step-by-step solution

(A) Carbonyl carbon is an electrophilic or Lewis acid centre

The carbonyl carbon has a double bond with the oxygen atom, which is more electronegative. This results in the carbonyl carbon having a partial positive charge, making it an electrophilic (electron-seeking) or Lewis acid center. This statement is correct.

(B) Carbonyl compounds have substantial dipole moments and are less polar than ether

The carbonyl group in carbonyl compounds indeed has a significant dipole moment due to the difference in electronegativity between the oxygen atom and the carbon atom. Generally, carbonyl compounds are more polar than ether compounds, which have a more evenly distributed electron density. This statement is incorrect.

(C) Carbonyl oxygen is a nucleophilic or Lewis base centre

The oxygen atom in a carbonyl group is more electronegative than the carbon atom, resulting in a high electron density. However, the carbonyl oxygen is considered to be an electrophilic or Lewis acid center instead of a nucleophilic or Lewis base center due to the electron cloud attracting electrophiles. So, this statement is incorrect.

(D) Carbonyl carbon and three atoms attached to it lie in the same plane and \(p\)-electron cloud is \(20^{60^{4}}\) and below the plane

The carbonyl carbon, the carbonyl oxygen, and the two other atoms directly connected to the carbonyl carbon lie in the same plane, obeying the principle of sp² hybridization. Additionally, the \(p\)-electron cloud is above and below the plane, with each part having a (rough) angle of 60 degrees, making a total of 120 degrees. The unusual notation presented in the exercise is incorrect; the angle should be written as 120°. While the overall idea is correct, the angle notation is incorrect in this statement. The incorrect statements are (B), (C), and (D).

Key concepts

Electrophilicity of Carbonyl Carbon

Understanding the electrophilicity of the carbonyl carbon is critical when studying carbonyl compounds. This carbon atom, found in the center of the carbonyl group, possesses a unique reactivity due to the polar bond it shares with an oxygen atom. Since oxygen is more electronegative, it pulls the shared pair of electrons towards itself, resulting in the carbon having a partial positive charge. This makes the carbonyl carbon an electrophile, or an electron-pair acceptor, often serving as a reactive site for nucleophilic attack in chemical reactions.

This propensity to attract nucleophiles makes carbonyl compounds involved in a wide range of organic reactions, such as the addition-elimination reactions commonly seen in organic synthesis. It is the nature of the electrophilic carbon that allows it to form bonds with various nucleophiles, expanding the versatility of carbonyl compounds in chemical synthesis.

Polarity of Carbonyl Compounds

The polarity of carbonyl compounds stems from the difference in electronegativity between the carbon and the oxygen atom of the carbonyl group. As oxygen is highly electronegative, it draws electrons towards itself, leading to a significantly polarized double bond. This polarization gives rise to a dipole moment, which is a measure of the separation of positive and negative charges within the molecule.

Comparatively, carbonyl compounds are more polar than ethers, which is contrary to what some may believe. The polarity in ethers is less pronounced due to the more evenly distributed electron density around the oxygen atom. In contrast, the pronounced polarity of carbonyl compounds imparts them with higher intermolecular forces and, consequently, higher boiling points. This is an essential concept as the polarity influences the solubility, reactivity, and intermolecular interactions of carbonyl-containing molecules.

Steric Arrangement of Carbonyl Groups

The steric arrangement, or the 3D spatial configuration, of carbonyl groups, is another crucial point in understanding their chemistry. In carbonyl compounds, the carbon and oxygen of the carbonyl group, along with two other substituents, lie in the same plane. This planarity is due to the sp² hybridization of the carbonyl carbon, which ensures a trigonal planar geometry.

The p-orbitals of both the carbon and oxygen atoms overlap to form the pi (π) bond in the carbonyl group, which lies perpendicular to the plane of the atoms. This planarity is significant because it affects the reactivity of the carbonyl group, especially when it comes to sterically hindered reactions. Moreover, the planar nature allows for the possibility of conjugation with other pi systems, which can influence the chemical properties and reactivity patterns of carbonyl compounds.