Carbocation and Charge Stabilization - Organic Chemistry - Lecture Slides, Slides of Organic Chemistry

Download Carbocation and Charge Stabilization - Organic Chemistry - Lecture Slides and more Slides Organic Chemistry in PDF only on Docsity! Carbocations & Charge Stabilization docsity.com Carbocations • Structures with a positive formal charge on carbon • What hybridization will carbocations have? – sp2 • What geometry will carbocations have? – trigonal planar R C R R docsity.com Electron Releasing Substituents • Inductive only – Alkyl groups • Resonance – Atoms with lone pairs – Alkenyl groups – Aromatic rings CH3 C CH3H3C H C CH3H3C H C HH3C is more stable than is more stable than tertiary C+, 3° secondary C+, 2° primary C+, 1° OH C CH3H3C OH C CH3H3C Structure has 1/2 of positive charge on each atom, much more stable than having the entire charge on one atom docsity.com Problem 1 • Draw resonance structures to demonstrate which atoms in the structure below share the positive charge H C H H H H H H docsity.com H C H H H H H H H C H H H H H H H C H H H H H H H C H H H H H H Notes on resonance forms: None of the Lewis structures to the right are exact representations of the electron and charge positions in the molecule (none actually exist and the molecule does NOT resonate between them) The behavior of the molecule is best described as a HYBRID of the resonance forms. H C H H H H H H +0.25+0.25 +0.25 +0.25 Notes on arrows: The double-headed arrows are used between resonance forms instead of reaction arrows, because NO reaction occurs Curved arrows are used to show movement of electrons (NOT atoms) Four Resonance Forms Resonance Hybrid docsity.com Electron Withdrawing Substituents • Electronegative atoms (at least those more electronegative than O): Br, Cl, I, F • Groups with positive (or partial positive charges) H C HH3C is more stable than primary C+, 1° H C HBr H C HH3C is more stable than primary C+, 1° H C HHC O docsity.com Problem 3 • Which of the groups below is the MOST electron-withdrawing? • Hint: draw out each complete Lewis structure with electrons, formal charges, and partial charges. NO2 Br C C O H O OCH3 docsity.com N O O Full formal positive charge on nitrogen makes this group very electron-withdrawing docsity.com