CHEM 203 Lecture Notes - Lecture 7: Atomic Orbital, Heteroatom, Carbocation
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How we should understand the addition of a nucleophile such as cl to a carbocation stabilized by a neighboring heteroatom (n, o, s): Ch3 better resonance structure for the cation: oxonium (imonium, sulfonium) form containing a new bond. It is easy to visualize a reaction from the poorer resonance structure of the carbocation: the nucleophile, cl in this case, will donate electrons into the vacant p-type atomic orbital of c: Orbital the new antibonding orbital will have larger lobes associated with the c atom (bond polarization makes the c atom quite positive) than with the o. A nucleophile, e. g. , cl , may then interact with the c atom (positive end of the bond dipole) and donate electrons into the antibonding orbital, breaking the bond and pushing electrons toward the o atom: General order of stability of carbocations: n/o/s-stabilized > tertiary > secondary > primary.
