Lesson28 - Nucleophilic Addition Reactions Adding XY Across...

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Nucleophilic Addition Reactions - Adding XY Across Unsaturated C=Z and C=C Bonds 1) Acid-Base - hydrogen swap 2 & 3) Oxidation & Reduction 4) Substitution - replace C’s substituent (-X) with another (-Y), neither being -H X C Y C Y + X + neither X nor Y being hydrogen Y replaces X 5) Elimination - loss of XY elements with concomitant pi bond formation 6) Addition - gain of XY elements with concomitant loss of pi bond reduction X C H C oxidation H replaces X X replaces H change in the number of C-H bonds in relation to the number of C-X bonds X C Z Z Y C + X Y elimination addition form π bond -XY break π bond +XY base H X H Y Y + X + base acid acid 7) Rearrangement - isomerization process (no atoms lost or gained); results in new bonding connectivity (one of many examples shown as there is no generic representation). R CH 3 R R stands for a generic "residue" Z = C, N, O We previously studied the electrophilic addition of “XY” across carbon-carbon multiple bonds. Here we examine the nucleophilic variations of addition. We will consider C=C and C=Z π -bonds (where Z is a heteroatom such as O or N).
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Nucleophilic Addition to Polarized π -Bonds: Three Examples CH 3 CH 2 MgBr O CH 3 H an aldehyde 2) H Cl / H 2 O 1) , Et 2 O a Grignard reagent H C H 3 C CH 2 CH 3 O H CH 3 O CH 3 H O H H B H H H Na NaBH 4 sodium borohydride NaB H 4 CH 3 O H C Na CN , H CN 80 ˚C C H H H C H NC H H H C O CH 3 C C O CH 3
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Addition Mechanisms Require a New Elementary Step: Nucleophile Addition to a C=O π -bond [Ad N ] Empty π * Filled n [Ad N ] involves σ -bond making and π -bond breaking σ n π σ a π σ→σ σ→ a σ→π filled empty n →σ n a n →π π→σ π→ a π→π Curved Arrows Imply the Frontier Orbitals Curved arrows indicate the HOMO-LUMO pair (Frontier Orbitals) involved in an elementary step.
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