Substitution Against Elimination: Predicting the Major Product · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.
En anglais

Picking the winner of four routes

Science · Chemistry · ages 19-21
Name ______________________   Date ____________

  1. How do nucleophile strength and base strength differ?

    • They are two names for the same property
    • Nucleophile strength attacks carbon, base strength grabs protons
    • Base strength attacks carbon, nucleophile strength grabs protons

  2. What is the first step when predicting substitution versus elimination?

    • Check the temperature first
    • Guess from the shape of the flask
    • Check the substrate class first

  3. Ordinary methyl and primary substrates forbid SN1 and E1.

    Circle one:   True   False

  4. Why does a bulky base favour the less substituted alkene from 2-bromo-2-methylbutane?

    • It reaches the least hindered proton fastest, favouring the less substituted alkene
    • It prefers crowded protons
    • Bulk always causes substitution instead

  5. 2-bromo-2-methylbutane meets a hindered alkoxide in warm alcohol. What dominates?

    • Direct SN2 substitution at carbon in this setup
    • Elimination to the less substituted alkene
    • No reaction at all

  6. In the taught two-path model, the elimination path climbs the higher barrier with the same attempt rate as substitution, barrier heights stay fixed over this temperature range, and the same two routes keep running. A contest runs warm that ran cool before. What happens to the elimination share?

    • It falls, since warmth slows every climb
    • Nothing changes, since temperature only touches gas reactions
    • It usually rises: heat helps the harder climb more

  7. Two routes follow fixed power laws in reagent with nothing else changing. Doubling the reagent leaves the product ratio unchanged. What does that tell you?

    • The competing routes share the same concentration dependence
    • A unimolecular route dominates, since it ignores concentration
    • Concentration was measured wrongly

  8. A student treats iodide as a strong base because it is a great nucleophile. What is the error?

    • Iodide is neither nucleophilic nor basic
    • Strength at carbon does not imply strength at protons, and iodide is a weak base
    • Bases never act as nucleophiles
LightMySky · lightmysky.comW1-mt_6WyFC9kQuu-s1

Answer key

For grown-ups. Fold this page away before handing over the rest.

Picking the winner of four routes W1-mt_6WyFC9kQuu-s1

  1. Nucleophile strength attacks carbon, base strength grabs protons · Iodide shows the split: great nucleophile, weak base.
  2. Check the substrate class first · Substrate class forbids routes before anything else matters.
  3. True · Ordinary ones cannot ionize; methyl also lacks a beta hydrogen, so only SN2 stays open for methyl while primary keeps SN2 and E2.
  4. It reaches the least hindered proton fastest, favouring the less substituted alkene · Reach decides. The open proton reacts fastest, favouring its route without forbidding the other.
  5. Elimination to the less substituted alkene · Tertiary forbids SN2, bulk blocks carbon, heat backs splitting.
  6. It usually rises: heat helps the harder climb more · With the higher barrier and the same attempt rate stated, warming lifts the harder climb relatively more, so elimination gains share.
  7. The competing routes share the same concentration dependence · With fixed orders and nothing else changing, no shift means neither route outruns the other; both answer alike.
  8. Strength at carbon does not imply strength at protons, and iodide is a weak base · Each strength belongs in its own place in the tree.
Worksheet · LightMySky