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SN1 SN2 E1 E2 Chart (Big Daddy Flowchart) quiz #1 Flashcards

SN1 SN2 E1 E2 Chart (Big Daddy Flowchart) quiz #1
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  • How can you determine whether a reaction proceeds via an SN1, SN2, E1, or E2 mechanism based on the nucleophile strength, base bulkiness, and alkyl halide structure?
    To determine the mechanism (SN1, SN2, E1, or E2), follow these steps: 1) Identify if the nucleophile is strong (negatively charged, often with spectator ions like Na+, K+, Li+, Cs+) or weak (neutral). 2) If strong and bulky (e.g., tert-butoxide, LDA, LiTMP), E2 is favored. 3) If strong but not bulky, check the alkyl halide: methyl/primary favor SN2, secondary can be SN2 or E2 (E2 if the base is strong, SN2 if not), tertiary favors E2 with strong bases. 4) If the nucleophile is weak/neutral, secondary and tertiary alkyl halides favor SN1/E1 (with heat favoring E1), while methyl/primary usually do not react. Thus, mechanism prediction depends on nucleophile strength, base bulkiness, and the degree of the alkyl halide.
  • What is the first question you should ask yourself when using the Big Daddy Flowchart to determine a reaction mechanism?
    You should ask whether the nucleophile is strong (negatively charged) or weak (neutral). This determines which pathway of the flowchart you follow.
  • Which four spectator ions commonly dissociate from nucleophiles to reveal their negative charge?
    The four spectator ions are lithium (Li+), sodium (Na+), potassium (K+), and cesium (Cs+). They do not participate in the reaction but help identify the nucleophile's charge.
  • What are the three bulky bases you should memorize for mechanism prediction?
    The three bulky bases are tert-butoxide, LDA, and LiTMP. These bases favor E2 elimination due to their size and basicity.
  • Why do methyl and primary alkyl halides favor SN2 reactions according to the flowchart?
    Methyl and primary alkyl halides have minimal steric hindrance, providing a good backside for nucleophilic attack. This accessibility makes SN2 the preferred mechanism.
  • What effect does heat have on the competition between SN1 and E1 mechanisms?
    Heat favors the E1 elimination mechanism over SN1 substitution. However, both mechanisms can occur simultaneously, with heat increasing the proportion of E1 products.
  • What happens when a neutral nucleophile reacts with a methyl or primary alkyl halide?
    No reaction occurs because methyl and primary alkyl halides cannot form stable carbocations. The combination of a weak nucleophile and poor carbocation stability prevents the reaction.
  • How does the flowchart help students who do not fully understand the underlying logic of the mechanisms?
    Memorizing and following the flowchart allows students to accurately predict mechanisms without deep conceptual understanding. This approach is especially useful for exam preparation and practice problems.
  • What is the significance of a nucleophile being better at donating electrons versus pulling off protons in mechanism determination?
    If a nucleophile is better at donating electrons, it favors substitution (SN2), while being better at pulling off protons favors elimination (E2). The flowchart uses this distinction to guide mechanism choice for secondary and tertiary alkyl halides.
  • Why can't a nucleophile with a positive charge be considered in the flowchart for SN1, SN2, E1, or E2 mechanisms?
    A positively charged species is an electrophile, not a nucleophile, and therefore cannot initiate nucleophilic substitution or elimination. Only neutral or negatively charged nucleophiles are relevant for these mechanisms.