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Ch.9 - Molecular Geometry and Bonding Theories
Chapter 9, Problem 44

Dihydroxybenzene, C6H6O2, exists in three forms (isomers) called ortho, meta, and para:
Structures of ortho, meta, and para isomers of dihydroxybenzene, showing dipole moments.
Which of these has a nonzero dipole moment?

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Identify the three isomers of dihydroxybenzene: ortho, meta, and para.
Understand that a molecule has a nonzero dipole moment if the individual bond dipoles do not cancel each other out.
Analyze the structure of ortho-dihydroxybenzene: the hydroxyl groups are adjacent, leading to a nonzero dipole moment due to the asymmetrical arrangement.
Analyze the structure of meta-dihydroxybenzene: the hydroxyl groups are separated by one carbon, leading to a nonzero dipole moment due to the asymmetrical arrangement.
Analyze the structure of para-dihydroxybenzene: the hydroxyl groups are opposite each other, leading to a zero dipole moment as the bond dipoles cancel each other out.

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Key Concepts

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

Isomerism

Isomerism refers to the phenomenon where compounds have the same molecular formula but different structural arrangements. In the case of dihydroxybenzene, the ortho, meta, and para isomers differ in the positions of the hydroxyl (-OH) groups on the benzene ring, leading to distinct physical and chemical properties, including dipole moments.
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Dipole Moment

A dipole moment is a measure of the separation of positive and negative charges in a molecule, indicating its polarity. Molecules with a nonzero dipole moment have an uneven distribution of electron density, resulting in a positive and a negative end. The orientation and arrangement of functional groups in isomers can significantly affect their dipole moments.
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Molecular Geometry

Molecular geometry describes the three-dimensional arrangement of atoms within a molecule. The spatial arrangement of atoms in ortho, meta, and para isomers of dihydroxybenzene influences their dipole moments. For instance, the ortho and meta isomers can exhibit nonzero dipole moments due to their asymmetrical structures, while the para isomer is symmetrical and typically has a zero dipole moment.
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