Chapter 11 - Arenes and Aromaticity Chapter 11 Aromatic...

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Arenes and Aromaticity Chapter 11 Aromatic Compounds i.e ., Arenes Arenes are cyclic conjugated compounds Benzene is the most common example – (Commonly drawn as a 6-membered triene) – …but, this is not the true structure! Aromatic compounds are much more stable than their analogous linear, conjugated structures is much more stable than
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Aromatic Compounds Common Examples • Benzene and toluene , are the simplest aromatic hydrocarbons Obtained from petroleum refining Useful starting materials for synthetic polymers. • Compounds with two or more benzene rings sharing carbon—carbon bonds are called polycyclic aromatic hydrocarbons . Anthracene Aromatic Compounds Higher Stability than Alkenes -85.8 kcal/mol - (-49.8 kcal/mol) = -36 kcal/mol Resonance energy
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• Whereas unsaturated hydrocarbons such as alkenes, alkynes and dienes readily undergo addition reactions, benzene does not. Aromatic Compounds Higher Stability than Alkenes Aromatic compounds are highly stable as compared to alkenes. Aromatic Compounds Structure of Benzene
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Aromatic Compounds Structure of Benzene Kekulé structures Aromatic Compounds Structure of Benzene 6 π electrons equally delocalized over 6 p orbitals High electron density above and below the plane of the ring
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Molecular orbital theory dictates that: – Bonding molecular orbitals are lower in energy than the component atomic orbitals – Antibonding orbitals are higher in energy than the component atomic orbitals Aromatic Compounds Molecular Orbital Theory – Therefore: • Increased number of bonding interactions decreases energy Increased stability • Increased number of antibonding interactions increases energy Decreases stability f To increase stability, maximize # of bonding interactions and minimize # of antibonding interactions Aromatic Compounds Molecular Orbital Theory All antibonding orbitals No decreased stability All bonding orbitals completely filled Increased stability completely empty
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• For benzene rings with one substituent, name the substituent and add the word “benzene.” Nomenclature of Benzene Derivatives Monosubstituted • Many monosubstituted benzenes have common names. • Three different ways that two groups can be attached to a benzene ring. • Prefixes - ortho , meta , or para - are used to designate the relative position of the two substituents. Nomenclature of Benzene Derivatives Disubstituted ortho -dibromobenzene or o -dibromobenzene or 1,2-dibromobenzene meta -dibromobenzene or m -dibromobenzene or 1,3-dibromobenzene para -dibromobenzene or p -dibromobenzene or 1,4-dibromobenzene
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• If the two groups are different, alphabetize the names of the substituents. • If one substituent is part of a common root, name the molecule as a
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This note was uploaded on 12/22/2011 for the course CHEM 3371 taught by Professor Anderson,k during the Fall '08 term at Southern Methodist.

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Chapter 11 - Arenes and Aromaticity Chapter 11 Aromatic...

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