Nucleophiles vs. Electrophiles PDF

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NUCLEOPHILES

ELECTROPHILES

“Nucleus-loving” Have either lone pairs or p bonds that can form new bonds to electrophiles.

“Electron-loving” Have a positive charge or positively polarized atom that accepts an electron pair when forming new bonds with a nucleophile.

Related to bases / basicity: Good nucleophiles tend to be good bases. Nucleophilic strength: based on relative rates of reaction with a common electrophile  Kinetic property Base strength: related to eqbm position of a rxn  Thermodynamic property

Greater degree of positive charge increases electrophilicity – carbocation is more electrophilic than a carbonyl carbon.

As long as nucleophilic atom is the same, the more basic the nucleophile, the more reactive it is. Also holds when comparing atoms in same row of periodic table (but NOT when proceeding down a column). Nucleophilicity is determined by 4 major factors: 1. Charge: nucleophilicity increases with increasing electron density (more negative charge) 2. Electronegativity: nucleophilicity decreases as electronegativity increases (these electrons less likely to share electron density) 3. Steric hindrance: bulkier molecules are less nucleophilic 4. Solvent: protic solvents can hinder nucleophilicity by protonating the nucleophile or through H bonding

In polar protic solvents: Nucleophilicity increases down the periodic table Nucleophilicity decreases in the order: I- > Br- > Cl- > FIn polar aprotic solvents: Nucleophilicity decreases down the periodic tables Nucleophilicity decreases in the order: F- > Cl- > Br- > INucleophilicity relates directly to basicity *Nonpolar solvents aren’t used in nucleophileelectrophile rxns (Rs are polar, they wouldn’t dissolve) Examples: 1. Strong nucleophiles: HO-, RO-, CN2. Fair nucleophiles: N3-, NH3, RCO23. Weak / v weak nucleophiles: H2O, ROH, RCOOH *Amino groups tend to make good nucleophiles

In a species without empty orbitals: the nature of the LG influences electrophilicity; better LGs make it more likely that a rxn will happen In a species with empty orbitals: nature of the LG doesn’t influence electrophilicity; incoming nucleophile can make a bond with the electrophile without displacing LG Related to acids / acidity: electrophiles almost always act as Lewis acids in rxns; electrophilicity & acidity effectively identical properties when it comes to reactivity Electrophilicity: kinetic property Acidity: thermodynamic property Functional groups that act as acids & electrophiles (make good targets for nucleophilic attack): 1. Alcohols 2. Aldehydes 3. Ketones 4. Carboxylic acids & their derivatives Most reactive to least: a) Anhydrides b) Carboxylic acids & Esters c) Amides *Derivatives of higher reactivity can form derivatives of lower reactivity but not vice versa....