Carbocations and Charge Stabilization | CHEM 3311, Study notes of Organic Chemistry

Download Carbocations and Charge Stabilization | CHEM 3311 and more Study notes Organic Chemistry in PDF only on Docsity! 1 Carbocations & Charge Stabilization 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 Carbocation Stability • Carbocations are inherently unstable due to – Incomplete octet for carbon – Positive charge • However, some are not as bad as others • Substituents that release electrons will stabilize carbocations by spreading the charge over a larger volume • Substituents that withdraw electrons will destabilize carbocations by packing a greater charge onto the carbon 2 Electron Release/Withdrawal Mechanisms • Induction – Induction involves the push and pull of electrons through sigma bonds – Example: bromine is more electronegative than carbon and will pull at the electrons in their sigma bond • Resonance => STRONGER EFFECT – Resonance involves the push and pull of electrons through a pi system 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 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