Orbitals in Organic Chemistry

Orbitals in Organic Chemistry - Orbitals in Organic...

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Orbitals in Organic Chemistry This guide to the lecture material and content of Orbitals in Organic Chemistry has been broken up into several broad categories which have then been arranged by page. This should NOT be used instead of lecture material, or relied solely upon for information, and I take no responsibility for any errors contained herein. 1. Contents and nomenclature 2. Orbitals in Organic Chemistry 4. Conjugation and orbitals HOMO-LUMO interactions 6. Nucleophilic substitution and Conformation S N 1 and hyperconjugation S N 2 and stabilisation of intermediates The Anomeric Effect and it’s rate on hydrolysis 11. Elimination and the Grob Fragmentation Pinacol rearrangement 12. The Diels Alder Reaction Dienes and dienophiles Stereochemistry of the Diels Alder reaction (Endo vs. Exo) Regiochemistry of the Diels Alder 19. Other Cycloaddition notes [2+2] cycloaddition Nitrone, Ozonolysis and Nitrile Oxide reactions [3+2] Pericyclic reactions (Cope, Claisen) Baldwin’s Rules for Ring Closure Important Nomenclature before beginning Orbitals in Organic Chemistry Chemical reactions always involve interactions between atomic or molecular orbitals, and are affected by three main factors – Energy levels Shape and size Symmetry Basic Principles There is an energetic gain in between atoms such as in CH 4 , relative to their constituent atomic orbitals. In the formation of a molecular orbitals, energy is released. Another example is in the formation of molecular bonds is between methyl units in ethane. Similarly signed orbitals lead to the formation of a lower energy molecular orbital. Non-like signed orbitals form a higher energy antibond (in this case, both are sigma, σ bonds). Bonding between p-orbitals forms pi bonds in a similar way to above. However, due to less favourable overlap, there is typically less energy gained from the pi bond than a sigma bond (except in some special cases such as N 2 and carbon monoxide).
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The orbitals diagram for carbonyls are similar (once sigma bonds are factored in), with the only real exception being that oxygen is lower in energy to carbon due to its electronegativity. Conjugation H ü ckel theory ckel theory is used to describe conjugated systems in terms of combinations of pi orbitals. One example is in butadiene which can be described as combinations of bonding pi orbitals and antibonding pi orbitals of ethene is various combinations. ψ 1 and ψ 2 are bonding ψ 3 and ψ 4 are bonding ψ 1 is lowered more than ψ 2 is raised. This stabilisation is a well known phenomenon in conjugated systems. Note the distribution of electrons in the molecular orbitals, denoted by the size of the orbitals. Note the symmetry and the position of the nodes within the molecular orbitals.
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This note was uploaded on 02/25/2012 for the course CHEM 2142 taught by Professor Roberts during the Fall '10 term at Texas State.

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Orbitals in Organic Chemistry - Orbitals in Organic...

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