Question

Which of the following carbon atoms is most electronegative? \(\mathrm{III} \quad \mathrm{n}\) \(\mathrm{CH}-\mathrm{CH}-\mathrm{C} \equiv \mathrm{CH}\) (a) III (b) II (c) I (d) All are equally electronegative

Short answer

The carbon atom III is the most electronegative.

Step-by-step solution

Understanding Electronegativity

Electronegativity is the tendency of an atom to attract a bonding pair of electrons. In general, the electronegativity of an atom is influenced by its hybridization state. Sp hybridized carbons are more electronegative than sp², and sp² is more electronegative than sp³.

Identifying Hybridization States of Carbons

In the molecular structure \[\text{CH}_1 - \text{CH}_2 - \text{C}_3 \equiv \text{CH}\], 1. Carbon I (\(\text{CH}_1\)) is bonded to two other atoms by sigma bonds, indicating an \( ext{sp}^3\) hybridization.2. Carbon II (\(\text{CH}_2\)) is bonded to three other atoms (two single bonds and one pi bond) indicating an \( ext{sp}^2\) hybridization.3. Carbon III (\(\text{C}_3\equiv \text{CH}\)) is involved in a triple bond, indicating an \( ext{sp}\) hybridization.

Comparing Electronegativity Based on Hybridization

The electronegativity order based on hybridization is \( ext{sp} > ext{sp}^2 > ext{sp}^3\). Therefore, the carbon with \( ext{sp}\) hybridization, which is Carbon III, is the most electronegative.

Selecting the Correct Option

Since Carbon III is the most electronegative due to its \( ext{sp}\) hybridization state, the correct answer is (a) III.

Key concepts

Hybridization and Electronegativity

Hybridization and electronegativity are closely linked concepts that help us understand how different hybridization states of carbon atoms influence their ability to attract electrons. Electronegativity is essentially how strongly an atom can pull electrons towards itself. This property is significant in determining the behavior of atoms in chemical reactions.
The hybridization of an atom influences its electronegativity primarily because of the s-character involved. An sp hybridized carbon atom has 50% s-character, making it more electronegative. It means these atoms are more tightly holding onto their electrons. In contrast, sp² hybridized carbons have 33% s-character, and sp³ hybridized have only 25% s-character, which makes them progressively less electronegative as the s-character decreases.
Understanding this concept is essential for predicting outcomes in organic chemistry, such as the reactivity of different carbon atoms in reactions.

Sp, Sp2, Sp3 Hybridization

Hybridization in chemistry refers to the mixing of atomic orbitals to form new hybrid orbitals suitable for pairing electrons to form chemical bonds. In organic molecules, carbon can form three primary hybridizations: sp, sp², and sp³.

• **Sp Hybridization**: Involves a linear shape using one s and one p orbital to form two identical sp orbitals. This type is seen in triple-bonded carbons, such as alkynes. Due to its high s-character (50%), it has strong electron-holding capacity.
• **Sp² Hybridization**: This hybridization involves mixing one s orbital with two p orbitals, forming three planar sp² hybrid orbitals. It is characteristic of double-bonded structures, like alkenes.
• **Sp³ Hybridization**: Occurs when one s and three p orbitals mix to create four tetrahedral sp³ orbitals. Seen in single-bonded structures such as alkanes, these carbons are more spread out, making them less electronegative.

Grasping these variations helps students predict how molecules will behave and interact with each other in reactions.

Electronegativity of Carbon Atoms in Organic Molecules

Understanding electronegativity in carbon atoms specifically within organic molecules is an area of great interest for chemists. It offers insights into how molecules might interact with each other in numerous biological and chemical processes.
In organic molecules, carbon atoms often take on sp, sp², or sp³ hybridization. Due to the varying degrees of electron-pulling power, electronegativity can influence the physical properties, such as boiling and melting points, and chemical properties, like acidity and reactivity.
Carbons with sp hybridization, as in alkynes, are more electronegative due to higher s-character. This makes them more capable of attracting electrons. Sp² hybridized carbons, found in alkenes, show moderate electronegativity. Finally, sp³ carbons, present in alkanes, are the least electronegative. Thus, electronegativity is vital in predicting how a molecule will stabilize its electrons and how it will behave in reactions.
Understanding these subtle differences helps explain why certain structures are more reactive or less stable under certain conditions.