Characteristic organic reactions

Need to know

What you need to know

• **Reagents:** Aqueous sodium hydroxide (for OH⁻), potassium cyanide in ethanol (for CN⁻), ammonia in ethanol (for NH₂).
• **Mechanism:** The mechanism depends on the structure of the halogenoalkane.
• **Primary (1°):** Undergo SN2 mechanism. A single step where the nucleophile attacks the carbon at the same time as the C-X bond breaks. The rate depends on the concentration of both the halogenoalkane and the nucleophile: Rate = k[RX][Nu⁻].
• **Tertiary (3°):** Undergo SN1 mechanism. A two-step process. First, the C-X bond breaks heterolytically to form a stable carbocation intermediate (rate-determining step). Then, the nucleophile rapidly attacks the carbocation. The rate depends only on the concentration of the halogenoalkane: Rate = k[RX].

Explanation

Organic Reaction Toolkit

1. Nucleophilic substitution: A nucleophile attacks the partially positive carbon in a halogenoalkane, kicking out the halogen. Primary halogenoalkanes prefer a one-step (SN2) process, while tertiary ones favour a two-step (SN1) route via a stable carbocation.
2. Electrophilic addition: The electron-rich C=C double bond in an alkene attacks an electrophile (like H⁺). This forms a carbocation intermediate, which is then attacked by a nucleophile. The initial attack follows Markovnikov's rule, forming the most stable carbocation.
3. Nucleophilic addition: The partially positive carbon of a carbonyl group (C=O) is attacked by a nucleophile (like CN⁻). The π-bond of the C=O breaks, and a new single bond is formed. Aldehydes are generally more reactive than ketones due to electronic and steric factors.
4. Condensation: Two molecules combine to form a larger molecule, with the elimination of a small molecule like water or HCl. This is key for forming esters (from a carboxylic acid and alcohol) and amides (from a carboxylic acid and amine).