Question

Which of the following is singlet carbene? (a) \(\left(\mathrm{CH}_{3}\right)_{3} \mathrm{C}\) (b) \(\mathrm{C}_{2} \mathrm{H}_{5} \ddot{\mathrm{C}}-\mathrm{H}\) (c) \(\mathrm{CH}_{3}-\dot{\mathrm{C}} \mathrm{HCH}_{3}\) (d) \(\mathrm{CH}_{2}=\mathrm{CH}-\mathrm{C} \mathrm{H}_{2}\)

Short answer

Option (b) \(\mathrm{C}_{2} \mathrm{H}_{5} \ddot{\mathrm{C}}-\mathrm{H}\) is the singlet carbene.

Step-by-step solution

Identify Singlet Carbene

A singlet carbene has two paired electrons in its valence shell on the carbon atom. To determine which compound is a singlet carbene, we need to identify the structure with no unpaired electrons.

Analyze Each Option

Review each molecule:- (a) \((\mathrm{CH}_{3})_{3} \mathrm{C}\) - This is a tert-butyl radical and not a carbene.- (b) \(\mathrm{C}_{2} \mathrm{H}_{5} \ddot{\mathrm{C}}-\mathrm{H}\) - This structure has a divalent carbon atom with two lone electrons, making it a carbene.- (c) \(\mathrm{CH}_{3}-\dot{\mathrm{C}}\mathrm{HCH}_{3}\) - This is an isopropyl radical.- (d) \(\mathrm{CH}_{2}=\mathrm{CH}-\mathrm{C} \mathrm{H}_{2}\) - This is an alkene, not a carbene.

Define the Correct Option

Option (b) \(\mathrm{C}_{2} \mathrm{H}_{5} \ddot{\mathrm{C}}-\mathrm{H}\) has a carbon with two lone pairs and shows no unpaired electrons, indicating it is a singlet carbene with paired electrons.

Key concepts

Carbene Reactivity

Carbenes are unique molecules known for their high reactivity. These compounds contain a divalent carbon atom with two available valence electrons. Understanding the behavior of carbenes is crucial as they often form during chemical reactions and can lead to the creation of new bonds.

• Carbenes can exist in two electronic states: singlet and triplet. Singlet carbenes have paired electrons, whereas triplet carbenes have unpaired electrons.
• Singlet carbenes are usually more reactive than triplet carbenes because their electrons can easily pair with electrons from other molecules.
• The reactivity of carbenes allows them to participate in addition reactions with double or triple bonds and insertion reactions.

To fully grasp carbene reactivity, it's essential to consider the nature of the electron pairs in the carbene, determining whether they are singlet or triplet.

Chemical Structure Analysis

Analyzing the chemical structure of a compound is fundamental in chemistry. It helps determine the properties and reactivity of the molecule. For carbene identification, examining the arrangement of atoms and electrons is critical.

• Each molecule has a particular structure that defines its behavior. In the context of identifying carbenes, look for carbon atoms that are divalent, meaning they are connected to other atoms with two bonds.
• By observing the Lewis structures of molecules, we can detect the presence of lone electron pairs, indicating if the molecule is likely a carbene.
• It's important to evaluate the symmetry and arrangement of atoms which can suggest the electronic state of the molecule, such as whether it's a singlet or triplet carbene.

Through careful chemical structure analysis, chemists can predict and explain the reactivity of molecules, improving their understanding and efficiency in chemical synthesis.

Valence Electrons

The concept of valence electrons is foundational to understanding chemical reactions and molecular structures. Valence electrons are the outermost electrons of an atom and play a significant role in forming bonds.

• For a carbene, the focus is on the presence and arrangement of valence electrons. Specifically, a singlet carbene is characterized by two paired valence electrons.
• These electron pairs determine the electronic configuration and influence the molecule's stability and reactivity.
• The presence of unpaired electrons often suggests higher reactivity, as seen in the comparison between singlet and triplet carbenes.

Understanding valence electrons aids in predicting how molecules will interact in chemical reactions, and for carbenes, it greatly affects their role and reactivity in various chemical processes.