Factors affecting nucleophilic substitution
For primary halogenoalkanes, the mechanism generally follows these steps: The nucleophile ( ) attacks the Cδ+cap C raised to the delta plus power from the side opposite the halogen. A transition state forms where the bond is forming while the bond is breaking. The halide ion ( X−cap X raised to the negative power ) leaves (the "leaving group"). 5. Elimination Reactions reactions of halogenoalkanes 1 chemsheets answers exclusive
Excess ammonia is used to prevent further substitution reactions where the amine itself acts as a nucleophile. 3. Trends in Reactivity (Rate of Reaction) Trends in Reactivity (Rate of Reaction) If you
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You should be comfortable drawing the "curly arrow" diagrams for: A one-step process (common for primary halogenoalkanes). A two-step process involving a carbocation intermediate (common for tertiary halogenoalkanes). Sₙ1 vs. Sₙ2 mechanism
| Factor | Favors Substitution (SN2 or SN1) | Favors Elimination (E2 or E1) | |---|---|---| | | Lower temp (25°C) | Higher temp (>60°C, reflux) | | Nucleophile/Base | Strong nucleophile, weak bulky base (e.g., OH⁻, CN⁻, NH₃) | Strong, bulky base (e.g., KOH in ethanol , not water; or tert-butoxide) | | Halogenoalkane structure | Primary (SN2 only); Tertiary (SN1) | Tertiary (E1 or E2); primary needs strong bulky base (E2) | | Solvent | Polar protic (water, alcohols) for SN1; Polar aprotic (DMSO, acetone) for SN2 | Polar protic also works; non-polar favors E2 |
Halogenoalkanes, also known as alkyl halides, are a class of organic compounds that contain a halogen atom (such as chlorine, bromine, iodine, or fluorine) attached to an alkyl group. These compounds are widely used in various industrial and laboratory applications, including as solvents, anesthetics, and intermediates in the synthesis of other organic compounds.