Draw the molecular orbital picture of trans-but-2-ene.

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Start by identifying the molecular structure of trans-but-2-ene. It is a four-carbon alkene with a double bond between carbons 2 and 3, and the two substituents on the double-bonded carbons are on opposite sides (trans configuration).

Determine the type of orbitals involved in the bonding. The double bond consists of one sigma (σ) bond formed by the overlap of sp² hybrid orbitals and one pi (π) bond formed by the side-by-side overlap of unhybridized p orbitals.

Draw the sigma framework first. Each carbon atom in the molecule is sp² hybridized, so three sp² orbitals on each carbon form sigma bonds: one with a hydrogen atom, one with another carbon atom, and one with the adjacent carbon in the double bond.

Next, represent the pi bond. The unhybridized p orbitals on carbons 2 and 3 overlap laterally to form the π bond. Ensure that the p orbitals are shown perpendicular to the plane of the molecule, as this is a key feature of π bonding.

Finally, label the molecular orbitals. The bonding molecular orbital (π) is formed by the in-phase overlap of the p orbitals, while the antibonding molecular orbital (π*) is formed by the out-of-phase overlap. Indicate the relative energy levels of these orbitals, with π being lower in energy than π*.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Molecular Orbitals

Molecular orbitals (MOs) are formed by the combination of atomic orbitals when atoms bond together. In the case of trans-but-2-ene, the MOs help describe the distribution of electrons in the molecule, which influences its stability and reactivity. Understanding how these orbitals overlap is crucial for visualizing the bonding and electronic structure of the compound.

Trans Configuration

Trans configuration refers to the arrangement of substituents across a double bond in a molecule. For trans-but-2-ene, the two methyl groups are positioned on opposite sides of the double bond, which affects the molecule's physical properties, such as boiling point and polarity. Recognizing this configuration is essential for accurately drawing its molecular orbital picture.

Hybridization

Hybridization is the concept of mixing atomic orbitals to form new hybrid orbitals that can accommodate bonding. In trans-but-2-ene, the carbon atoms undergo sp² hybridization, resulting in three sp² hybrid orbitals for sigma bonding and one unhybridized p orbital for pi bonding. This understanding is vital for constructing the molecular orbital diagram and predicting the molecule's geometry.

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Textbook Question

Suggest an alkene to undergo hydroboration–oxidation (1. BH₃ 2. NaOH, H₂O₂) to give exclusively the alcohols shown. Pay close attention to the relative (but not absolute) stereochemical outcome.

(b)

838

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Textbook Question

What is the index of hydrogen deficiency for each of the following molecular formulas?

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Textbook Question

Provide the IUPAC names for the following alkenes.

(a)

1405

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