Question

For 1,3-butadiene, there are ____ molecular orbitals for п electrons

• A. 2
• B. 4
• C. 6
• D. 8

Answer 1

The Correct Option is B

To determine the number of molecular orbitals for the π electrons in 1,3-butadiene, we can follow these steps:

1. 1,3-Butadiene is a conjugated diene with the molecular formula \(C_4H_6\). It has a chain of four carbon atoms, two of which are connected in succession by double bonds. 
2. In conjugated systems, the number of molecular orbitals formed is equal to the number of atomic orbitals involved, which in this case refers to the p orbitals that participate in π-bonding.
3. Each carbon atom in the double bond contributes a p orbital for the formation of π molecular orbitals. Therefore, for 1,3-butadiene, there are four carbon atoms, each providing one p orbital for π bonding.
4. These four p orbitals combine to form four π molecular orbitals: two bonding and two anti-bonding. These are designated as \(π_1, π_2, π_3^*,\) and \(π_4^*\), where \(π_1\) is the lowest energy (most stable) bonding orbital, \(π_2\) is another bonding orbital, and \(π_3^*\) and \(π_4^*\) are antibonding orbitals.

Therefore, the correct answer is 4:

• Option 2: 4 - This is the correct number of molecular orbitals formed by the p orbitals involved in the π-bonding of 1,3-butadiene.
• Options 1, 3, and 4 (2, 6, 8 respectively) are incorrect because they do not match the number of available p orbitals in 1,3-butadiene.

Hence, for 1,3-butadiene, there are four molecular orbitals formed for π electrons.