CHEM 261 1st Edition Lecture 15Outline of Last Lecture:I. Review of Last LectureII. Reaction GraphsIII. Reaction MechanismsIV. Polar ReactionsOutline of Current Lecture:I. Electrophiles and Nucleophiles as Functional GroupsII. Using Arrow FormalismIII. Polar Addition of H-Br to EthyleneIV. Degrees of UnsaturationV. Naming AlkenesElectrophiles and Nucleophiles as Functional Groups:-Most cases, the central carbon of the functional group will have the partial positive charge and be the electrophile. Therefore, the partial positive charge is usually what is attached to the carbon and will have high electronegativity, making it the nucleophile. Using Arrow Formalism:-Curved arrows indicate electron movement-Straight arrows can mean a variety of things, but most commonly will indicate the progression of a reaction**remember that you always move electrons to either make/break a bond****half arrow= radical (1 electron), full arrow = electron pair (2 electrons)****if you push an electron pair (make a bond) with an atom that already has a completed octet, you then must break a bond**Polar Addition of H-Br to Ethylene:-The reaction is polar-alkene is the nucleophile and H-Br is the electrophile based on the INITIAL STEPS of the reaction!!**Double bond (π bond) is VERY electron rich-Also note that the reaction is 2 steps and has an intermediateDegrees of Unsaturation:-Hydrocarbons = H’s and C’s-elements of unsaturation: double bonds between carbons(Saturated hydrocarbon = only single bonds)**alkenes may also be referred to as olefins(notes continued next
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