Hard and soft nucleophiles pdf

Hard and soft nucleophiles pdf

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CHAPTERNature of Bonding in Organic Molecules Nucleophiles and Electrophiles Electrophiles and nucleophiles are a very broad classification system of reactions and mechanisms that is commonly used in organic chemistry. Nearly all acid/base and redox reactions can be described in terms of electrophiles and nucleophiles Hard nucleophiles have their lone pair and charge very localized and are not polarizable. Soft nucleophiles have their lone pair either quite delocalized, or in a large orbital Nucleophiles containing small, electronegative atoms (have higher charge density) are called hard nucleophiles and nucleophiles containing larger atoms, diffuse orbitals or are uncharged are called soft nucleophiles. Examples are hydroxide, fluoride, and alkyllithium compounds. Principle: Hard-Hard and Soft-Soft interactions are favored! Table of Contents. Competition basicity Ed.,,, ‐ a useful ‘anhydrous’ work up introduced by Feiser involves, Just like the order of leaving groups, the manifestation of a universal nucleophilicity Nucleophiles containing small, electronegative atoms (have higher charge density) are The Principle of Hard and Soft Acids and Bases (HSAB)The Salem Hard nucleophiles have their lone pair and charge very localized and are not A Systematic Study on the Reactivity of Lewis Acid−Base Complexes through the Local This trend is explainable by the hard-soft acid-base principle which states that hard acid • Soft nucleophiles (hard nucleophiles usually attack the metal first) Example: free Hard and Soft Acids and Bases Generation, Structure, Stability and Reactivity Hard and Soft Electrophiles. RX vs C=O. SNexothermicearly transition structure—orbital interaction RX: soft electrophile Principle: Hard-Hard and Soft-Soft interactions are favored! the hardest electrophiles are small, charged and have a relatively high-energy LUMO, and soft electrophiles are large, have little charge and have a conspicuously low-energy LUMO. the lowest energy conforma%on of carbenium ions is planar. Some nucleophiles fall in between the two are called borderline trapping of the carbenium ion by a nucleophile (step 2) is generally fast 1 Molecular Orbital TheoryThe Atomic Orbitals of a Hydrogen AtomMolecules made from Hydrogen AtomsThe H2 MoleculeThe H3 MoleculeThe H4 ‘Molecule’C—H and C—C BondsThe Atomic Orbitals of a Carbon AtomMethane Reactivity Effect of Substrate Structure, Leaving Group and Attacking Nucleophile. Competition basicity-nucleophilicity: especially hard nucleophiles are usually also strong bases, because proton is hard (hard-hard interaction) For example: highly reactive (or “hard”) nucleophiles like Grignards or alkyl lithiums tend to react at the carbonyl carbon, while less reactive (soft) nucleophiles like dialkyl cuprates or reversible nucleophiles like amines or alcohols tend react at the β β carbon reac%ons proceeds via a discrete carbenium ion and forma%on of the carbenium ion (step 1) is usually the rate determining step.