Azulene, an isomer of naphthalene, has a remarkably large dipole moment for a hydrocarbon (μ=1.0

step 1 Solving problem 17 of chapter 15 so we need to explain why the molecule called azuline as a larg

Azulene, an isomer of naphthalene, has a remarkably large...

Key Concepts

Resonance Structures

Resonance structures are alternate Lewis structures for a molecule which depict different possible distributions of electrons. They do not represent different molecules but rather contribute to the resonance hybrid, which is the actual, more stable structure. In molecules with conjugated systems, such as some aromatic compounds, these forms help explain how electrons are delocalized, leading to stabilization and influences on molecular properties.

Molecular Dipole Moment

The molecular dipole moment is a measure of the separation of positive and negative charges within a molecule. Even in hydrocarbons, if the electron distribution is uneven due to structural or electronic factors, a significant dipole moment can arise. It is essentially the vector sum of individual bond dipoles and any overall asymmetry in the charge distribution, which can be rationalized by the presence of resonance structures that feature partial charge separation.

Aromaticity

Aromaticity refers to a property of cyclic molecules with a conjugated pi-electron system that leads to enhanced stability relative to non-aromatic compounds. In particular, aromatic systems display electron delocalization over a ring, which can sometimes result in electronic asymmetries. In certain isomers of aromatic compounds, variations in electron delocalization can lead to distinct regions of electron density, contributing to observable physical properties like a dipole moment.

Charge Separation in Resonance

Charge separation in resonance involves the depiction of structures where positive and negative charges are distributed unevenly across the molecule. These resonance forms suggest that, even in a neutral molecule, there can be regions of partial positive and negative character. This internal separation of charge, when averaged over all contributing structures, explains why some molecules, despite having an overall balanced formula, exhibit a measurable dipole moment.

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