20080402 Mole 6 Spect 1

20080402 Mole 6 Spect 1 - Intro Chemistry II 030.102...

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Intro Chemistry II – 030.102 Spring, 2008 1 Example 16.4 Lewis diagram for propyne (CH 3 CCH) is Discuss its bonding and predict its geometry. Structural Isomerism An isomer of propyne is allene (H 2 CCCH 2 ). What is geometry? Outer C atoms have sp 2 hybridization, central C atom sp hybridized . Carbon atoms have linear geometry. CH 2 planes perpendicular to each other.
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Intro Chemistry II – 030.102 Spring, 2008 2 Structural Isomerism Second type of isomerism – optical isomers or chirality . Important example: carbon atom with 4 different substituents (related by mirror plane reflection). Rotates plane of polarized light in different directions, said to be optically active . Biological molecules (amino acids, proteins, etc.) Conjugated Molecules Delocalized MO picture should be used when double or triple bonds adjacent to each other. Example : 1,3-butadiene (CH 2 CHCHCH 2 ). Lewis diagram: All the C atoms have steric number 3, sp 2 hybridized. The p z orbitals have maximum overlap with all 4 C atoms in a plane. Molecule planar. After filling σ bonding orbitals, 4 electrons left for π orbitals. Lowest-energy orbitals: bonding combination for all 4 C atoms, next orbital: 1-2, 3-4 bonding but 2-3 anti-bonding. Conjugated -electron system – alternating single and multiple (double or triple) bonds.
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Spring, 2008 3 Conjugated Molecules The four π MO’s for 1,3-butadiene. Note the nodes in the orbitals. These 2 MO’s doubly occupied in ground-state electron configuration Conjugated Molecules Important example of conjugated -electron system: benzene (C 6 H 6 ) Lewis structure is resonance hybrid of two diagrams: Modern view: electrons do not jump between the 2 configurations. Molecule has single, time-independent electron configuration with delocalized Kekulé (1865)
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This note was uploaded on 04/14/2008 for the course CHEMISTRY 102 taught by Professor Dagdigian during the Spring '08 term at Johns Hopkins.

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20080402 Mole 6 Spect 1 - Intro Chemistry II 030.102...

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