Overview
This lecture introduces electrophiles and nucleophiles in organic chemistry, explains their interactions through nucleophilic attacks, and demonstrates the importance of reaction mechanisms and experimental confirmation via IR spectroscopy.
Electrophiles and Nucleophiles
- Electrophiles are electron-poor species attracted to electron-rich regions; they act as Lewis acids.
- Nucleophiles are electron-rich species attracted to positive charges; they act as Lewis bases.
- Lewis acids accept electron pairs; Lewis bases donate electron pairs.
- Examples of nucleophiles: ammonia, water, hydroxide ion, chloride ion.
- Examples of electrophiles: protons, carbocations, borane (BH₃).
Nucleophilic Attack and Mechanisms
- A nucleophilic attack occurs when a nucleophile donates electrons to an electrophile.
- Curved arrows in mechanisms always start from the nucleophile and point to the electrophile.
- Nucleophilic substitution reactions involve the replacement of one group (like halide) by a nucleophile.
- Reactions can be single-step (direct substitution) or multi-step (e.g., via carbocation intermediates).
Reaction Examples
- Hydroxide attacks 1-chlorobutane, substituting for chlorine to produce butan-1-ol and chloride ion.
- Carbocations are highly reactive electrophiles, easily attacked by nucleophiles like water.
- Alkene double bonds can act as nucleophiles, attacking acids like HBr in two-step addition reactions.
- Cyanide ion acts as a strong nucleophile to form new carbon-carbon bonds via nucleophilic substitution.
Experimental Confirmation
- Infrared (IR) spectroscopy can be used to verify reaction products by identifying functional groups, such as alcohol O-H bonds.
Key Terms & Definitions
- Electrophile — Electron-poor species that accepts electron pairs (Lewis acid).
- Nucleophile — Electron-rich species that donates electron pairs (Lewis base).
- Nucleophilic attack — Reaction where a nucleophile donates electrons to an electrophile.
- Carbocation — Positively charged carbon atom (sp² hybridized, empty p orbital).
- Nucleophilic substitution — Reaction where a nucleophile replaces another group in a molecule.
- IR spectroscopy — Analytical technique to identify functional groups by measuring bond vibrations.
Action Items / Next Steps
- Review nucleophilic substitution reaction mechanisms and IR spectra analysis.
- Prepare for the next lesson on reaction mechanisms and advanced arrow pushing.