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Chapter2 - Structure and Structure properties of organic...

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2- 2-1 Structure and Structure and properties of properties of organic organic molecules molecules Chapter 2 Chapter 2
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2- 2-2 Quantum or Wave Mechanics Quantum or Wave Mechanics Albert Einstein: E = h ν (energy is quantized ) light has particle properties Louis deBroglie: wave/particle duality Erwin Schrödinger: wave equation wave function, wave function, ψ ψ : a solution to a set of equations that depicts the energy of an electron in an atom each wave function is associated with a unique set of quantum numbers each wave function occupies three-dimensional space and is called an orbital orbital λ = h m ν
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2- 2-3 Shapes of 1 Shapes of 1 s s and 2 and 2 s s Orbitals Orbitals Probability distribution ( ψ 2 ) for 1 s and 2 s orbitals showing an arbitrary boundary surface containing about 95% of the electron density
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2- 2-4 Shapes of a Set of 2 Shapes of a Set of 2 p p Atomic Orbitals Atomic Orbitals Three-dimensional shapes of 2 p atomic orbitals
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2- 2-5 Molecular Orbital Theory Molecular Orbital Theory Electrons in atoms exist in atomic orbitals Electrons in molecules exist in molecular orbitals (MOs) Using the Schrödinger equation, we can calculate the shapes and energies of MOs
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2- 2-6 Molecular Orbital Theory Molecular Orbital Theory Rules: combination of n atomic orbitals (mathematically adding and subtracting wave functions) gives n MOs (new wave functions) MOs are arranged in order of increasing energy MO filling is governed by the same rules as for atomic orbitals: Aufbau principle: fill beginning with LUMO ( lowest unoccupied molecular orbital) Pauli exclusion principle: no more than 2e - in a MO Hund’s rule: when two or more MOs of equivalent energy are available, add 1e - to each before filling any one of them with 2e -
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2- 2-7 Molecular Orbital Theory Molecular Orbital Theory Terminology ground state = lowest energy state excited state = NOT lowest energy state σ = sigma bonding MO σ * = sigma antibonding MO π = pi bonding MO π * = pi antibonding MO HOMO = highest occupied MO LUMO = lowest unoccupied MO
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2- 2-8 Molecular Orbital Theory Molecular Orbital Theory Bonding of H 2 H H 1s a 1s b MOLECULAR ORBITAls 1sa + 1sb = psi+
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2- 2-9 Molecular Orbital Theory Molecular Orbital Theory MO energy diagram for H 2 : (a) ground state and (b) lowest excited state
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2- 10 10 Molecular Orbitals Molecular Orbitals computed sigma bonding and antibonding MOs for H 2
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2- 11 11 Molecular Orbitals Molecular Orbitals pi bonding and antibonding MOs
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2- 12 12 Molecular Orbitals Molecular Orbitals computed pi bonding and antibonding MOs for ethylene
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2- 13 13 Molecular Orbitals Molecular Orbitals computed pi bonding and antibonding orbitals for formaldehyde
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2- 14 14 Shapes of Molecules: VSEPR Shapes of Molecules: VSEPR Based on the twin concepts that atoms are surrounded by regions of electron density regions of electron density repel each other H C C H O C C H N H H C H H O H C H C H H O 4 regions of e -
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