As you move down Group 7, the halogen atoms get larger. The shared pair of electrons is further from the nuclei, making the bond longer and weaker. Bond Enthalpy ( kJ mol-1kJ mol to the negative 1 power Reactivity C-F Extremely unreactive (strong bond) C-Cl Moderately reactive C-Br C-I Highly reactive (weakest bond) Key Takeaway: Even though the
This reaction increases the carbon chain length, forming a nitrile. in ethanol/water mixture. Conditions: Heat/Reflux. Key Reaction: Example (1-bromobutane + ethanolic KCN): The product is pentanenitrile . C. Reaction with Ammonia (
Both reactions start with the same halogenoalkane and a base/nucleophile (e.g., OH⁻). The outcome depends on: reactions of halogenoalkanes 1 chemsheets answers exclusive
The nucleophile attacks the planar carbocation. Because the carbocation is flat, the nucleophile has an equal (50/50) probability of attacking from either the front or the back. If the starting material was optically active, this results in a racemic mixture (optically inactive). Rate Law:
“Explain why 2-iodo-2-methylpropane gives a precipitate instantly with AgNO₃(aq), but 1-iodopropane takes several minutes.” Model Answer: “2-iodo-2-methylpropane is tertiary, so it undergoes SN1 reaction via a stable carbocation, leading to rapid release of I⁻ ions. 1-iodopropane is primary and must undergo slower SN2 reaction, requiring backside attack before I⁻ leaves.” As you move down Group 7, the halogen atoms get larger
: Always start from a lone pair or the center of a bond.
Aqueous sodium hydroxide or potassium hydroxide (OH⁻). The Condition: Warm, aqueous solution. The Product: Alcohol. The Mechanism: Nucleophilic Substitution (SN1 or SN2 depending on the structure). in ethanol/water mixture
The electron-deficient carbon atom acts as an electrophile, making it highly susceptible to attack by electron-rich species. Bond Enthalpy vs. Bond Polarity
Chemsheets exercises place heavy emphasis on predicting products, conditions, and writing balanced equations for three fundamental nucleophilic substitutions. Reaction with Aqueous Hydroxide Ions ( OH−OH raised to the negative power Sodium hydroxide ( ) or potassium hydroxide ( Conditions: Aqueous solution, heated under reflux. Product: Alcohol. Equation:
Crucial Trick: must be used. If the halogenoalkane is in excess, the newly formed primary amine (which still has a lone pair on the nitrogen) will act as a nucleophile and attack remaining halogenoalkanes, leading to secondary, tertiary, and quaternary ammonium salts. 3. Elimination Reactions Under different environmental conditions, hydroxide ions ( OH−OH raised to the negative power