Question

Divalent carbon species called carbenes are capable of fleeting existence. For example, methylene, \(: \mathrm{CH}_{2}\), is the simplest carbene. The two unshared electrons in methylene can be either spin-paired in a single orbital or unpaired in different orbitals. Predict the type of hybridization you expect carbon to adopt in singlet (spin-paired) methylene and triplet (spinunpaired) methylene. Draw a picture of each, and identify the valence orbitals on carbon.

Short answer

Singlet methylene has \(sp^2\) hybridization; triplet methylene has \(sp\) hybridization.

Step-by-step solution

Understand Methylene

Methylene, \(: CH_2\), is a divalent carbon species known as a carbene. It contains a carbon atom with two hydrogen atoms and two unshared electrons, which can either be spin-paired or spin-unpaired.

Identify Hybridization in Singlet Methylene

In singlet methylene, the two unshared electrons are spin-paired in a single orbital. Carbon does not need hybrid orbitals to accommodate the two hydrogens and can remain in an \(sp^2\) hybridized state, as the remaining p-orbital accommodates the lone pair of electrons which are paired.

Visualize Singlet Methylene

Draw a diagram of the singlet methylene with the carbon atom in the center, bonded to two hydrogens. Depict one \(sp^2\) orbital containing the lone pair and two \(sp^2\) orbitals forming the carbon-hydrogen bonds. The unhybridized p-orbital remains empty.

Identify Hybridization in Triplet Methylene

In triplet methylene, the two unshared electrons are spin-unpaired, each occupying different orbitals. The carbon is \(sp\) hybridized, with the two unpaired electrons residing in the two remaining unhybridized p-orbitals.

Visualize Triplet Methylene

Draw a diagram of the triplet methylene with the carbon atom in the center, bonded to two hydrogens. Show the carbon with \(sp\) hybrid orbitals for bonds, and two perpendicular unhybridized p-orbitals each containing one unpaired electron.

Conclusion on Valence Orbitals

In singlet methylene, carbon has two \(sp^2\) hybrid orbitals for bonding and another \(sp^2\) orbital that contains a lone pair. In triplet methylene, carbon uses \(sp\) hybrid orbitals for bonding with two hydrogens and two separate p-orbitals for unpaired electrons.

Key concepts

Hybridization

In the fascinating world of chemistry, hybridization is a concept that helps explain how atomic orbitals mix to facilitate bonding in molecules.
Let's explore how this applies to methylene, a type of carbene.

• Singlet Methylene: In this form, the carbon atom is in an \(sp^2\) hybridized state. This means one s orbital mixes with two p orbitals, resulting in three equivalent \(sp^2\) orbitals.
• Triplet Methylene: Here, carbon adopts an \(sp\) hybridization, which is a combination of one s orbital with one p orbital, leaving two unhybridized p orbitals. This configuration is essential for hosting unpaired electrons.

Hybridization in methylene is crucial as it dictates how the electrons are arranged and how bonds are formed.

Methylene

Methylene \((: \mathrm{CH}_2)\) is the simplest example of a carbene, possessing unique properties due to its divalent carbon and two unshared electrons.
Let's delve into its characteristics:

• Spin-Paired (Singlet): In singlet methylene, the two unshared electrons are paired in a single orbital. This creates a more stable form with less reactivity as the electrons are not free to participate in further bonding or reactions.
• Spin-Unpaired (Triplet): Conversely, triplet methylene has electrons in separate orbitals, which makes it highly reactive.

The behavior of methylene in these forms significantly influences its reactivity and the roles it plays in various chemical reactions.

Valence Orbitals

Valence orbitals are the orbitals that hold the electrons used in bonding. In methylene, understanding valence orbitals is key to predicting its reactivity and bonding behavior.

• In Singlet Methylene: The carbon atom employs two \(sp^2\) orbitals for bonding with hydrogen atoms, while the third \(sp^2\) orbital holds the lone pair, and an unhybridized p orbital remains empty.
• In Triplet Methylene: The carbon uses \(sp\) hybrid orbitals for bonding, with two p orbitals containing unpaired electrons, making it a diradical species.

The spatial arrangement and occupation of these valence orbitals determine the chemical properties and potential interactions of methylene with other molecules.