CH 221 1st Edition Lecture 23 Outline of Last Lecture I. Terminal and Internal AlkynesII. Lindlar CatalystsIII. Carbon-Carbon BondsIV. Reaction SubstitutionV. Inverted ConfigurationOutline of Current Lecture VI. Base Strength and Nucleophile StrengthVII. Ion-Dipole InteractionsVIII.SN2 ReactionsCurrent LectureVI. The weakest base is the best leaving group- Relative basicity of halide ions- Weakest I < Br < Cl < F strongest but least stable- Most reactive RI > RBr > RCl > RF too unreactive- The rate of the SN2reaction is effected by leaving groups- Strongest base, best nucleophile −¿NH2¿ > −¿HO¿ > −¿F¿- If atoms are on the same row the strongest base is the best nucleophile- A negatively charged atom is a stronger base and better nucleophile than the same atombut neutralVII. Ion-Dipole Interactions- Stronger bases form stronger ion-dipole interactions- Ion-dipole interactions have to be broken before a nucleophile can reactThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.- The strongest base is the best nucleophile unless: 1. They differ in size 2. They are in a protic polar solvent- F is the best nucleophile in a protic solvent- I is the best nucleophile in an aprotic solvent- Steric hindrance decreases nucleophilicity - Even though the tert-butoxide ion is a stronger base, it is a poorer nucleophile because the nucleophilic attack is more sterically hindered than proton removal- Reactions are irreversible because a strong base replaces a weaker baseVIII. SN2reactions can be used to make many compounds- A tertiary alkyl halide and a poor nucleophile is surprisingly fast so a different mechanism must be taking place- Rate=k[alkyl halide] in a SN1 reaction- Rate depends only on alkyl halide- Generally only tertiary alkyl halides undergo SN1
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