Chapter 13, Problem 37P

Interpretation Introduction

Interpretation:

The molecular orbital diagram for ground state of cyclopentadiene is to be completed; appropriate lobes are to be shaded to indicate the phase signs. HOMO and LUMO orbitals are to be labeled. Appropriate number of electrons, using straight single-barbed arrows in each level, is to be represented.

Concept introduction:

舧 Molecular orbital diagrams are used to explain the linear combination of atomic orbitals.

舧 HOMO and LUMO are types of molecular orbitals and are abbreviations for highest occupied molecular orbital and lowest unoccupied molecular orbital, respectively.

舧 Each lobe is a representation of p-orbital and each lobe has two poles, that is, shaded and non-shaded regions.

舧 The orbitals are aligned in such a way that each double bond in cyclopentadiene has the same orbitals.

舧 The lowest energy position is where all orbitals are shaded on top and clear on bottom.

舧 The second energy level has one orbital overlap.

舧 Third energy level has no orbital overlap but the two orbitals in the same alignment create similar signs through-space conjugation.

舧 Fourth energy level has no orbital overlaps or no sign changes and hence, it is the most unstable.

舧 There are two pi-bonds in cyclopentadiene, meaning 4 pi-electrons present in the system.

舧 The pi-electrons fill the lowest energy level.