AS P1: Organic #chemistry #9701 #science #p1

The provided source material covers key concepts in organic chemistry, focusing on reaction mechanisms, the stability of benzene, and electronic trends affecting acidity and basicity. Substitution vs. Elimination Mechanisms Halogenoalkanes react differently depending on the conditions and their structure: Nucleophilic Substitution: This occurs when halogenoalkanes are exposed to aqueous sodium hydroxide (NaOH) under reflux. Primary halogenoalkanes follow a single-step $S_N2$ mechanism that involves a transition state. Tertiary halogenoalkanes undergo a multi-step $S_N1$ mechanism characterized by a stable carbocation intermediate. Elimination Reaction: If the conditions are shifted to hot, ethanolic sodium hydroxide, the reaction produces an alkene, water, and a halide ion instead of undergoing substitution. Arenes and Electrophilic Substitution Benzene's unique structure dictates its reactivity: Stability: Benzene has a planar, symmetrical ring stabilized by a delocalized pi-electron cloud above and below the carbon framework. This makes it highly resistant to standard addition chemistry. Electrophilic Substitution: Because the concentrated electron cloud attracts electrophiles, benzene favors substitution. Nitration: For nitration, the active electrophile is the nitronium ion ($NO_2^+$), which is synthesized using a mixture of concentrated nitric and sulfuric acids. Acidity and Basicity Electronic Trends The sources explain how molecular structure influences the strength of acids and bases: Acidity of Phenol: Phenol is significantly more acidic than ethanol. This is because the lone pair on the oxygen atom overlaps with the delocalized aromatic ring, which stabilizes the resulting phenoxide ion. Basicity of Amines: Basicity is determined by how available a nitrogen lone pair is to accept a proton. Ethylamine is a stronger base than ammonia due to the electron-donating inductive effect of its alkyl group. Phenylamine is a weaker base because its nitrogen lone pair delocalizes directly into the benzene ring system, making it less available. #chemistry #9701 #0620 #5070 #5070chemistry #caie #p1 #alevelchemistry