272_reactions - A B A B homolytic cleavage A B A B...

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Chain Chem 272 Bonds and Reactions Bonding • What is a bond? Put simply - constructive orbital overlap. (Is it really a happy sharing of electrons?) • The simplified picture: orbital on less EN element orbital on more EN element Ionization Potential Bonding interaction Antibonding interaction A B A B A B •Check out chapter 4 of your book for discussions of orbitals and bonds. What kind of bond is it? Check electronegativities! (see below) • Non-polar covalent bond : Δ EN < 0.5 ex. C–H • Polar covalent bond : 0.5 < Δ EN < 2.0 ex. C–Li or C–Cl • Ionic bond : Δ EN > 2.0 ex. NaCl Reactions • The arrow-pushing convention: show where electrons are going. - single-headed arrow means one electron is moving. ex: - double-headed arrow means two electrons moving. ex:
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Unformatted text preview: A B A B homolytic cleavage A B A B heterolytic cleavage Get used to this! Reactions (cont'd) • What is a reaction? Put simply - an orbital interaction (a filled orbital with an empty orbital, or HOMO–LUMO interaction) that makes or breaks bonds • The simplified picture: A B filled orbital (HOMO) nucleophile Nu-empty orbital (LUMO) electrophile E + A B note new bond is a new orbital created from the HOMO and LUMO Real life examples: N H 3 C CH 3 CH 3 trimethylamine F B F F boron trifluoride LUMO empty p HOMO full sp 3 B N H 3 C F CH 3 F F CH 3 new bond sp 3 (N) - sp 3 (B) Br C N Identify Product, HOMO/LUMO in starting materials H 3 C O CH 3 C N...
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