Asymmetric Catalysis: Where Enantioselectivity Comes From · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

One face open, one face blocked

Science · Chemistry · ages 22-23
Name ______________________   Date ____________

  1. Mirror-image molecules share every property except how they twist light and fit handed partners.

    Circle one:   True   False

  2. A drug comes in two mirror forms. Which difference between the hands is possible?

    • Their masses on a balance
    • How they fit a handed partner in the body
    • The count of each atom

  3. Which helper is spent instead of turning over?

    • A chiral catalyst
    • An enzyme pocket
    • A chiral auxiliary

  4. A reaction gives 75 percent excess. What percent of the product is the major hand?

    Answer: ______________

  5. A ligand keeps its grip but gains a bulkier blocking arm, and the run still reacts briskly. What usually happens to the excess?

    • It rises, since the blocked face climbs higher
    • It falls, since bulk always slows the open face
    • It stays fixed, since only temperature sets it

  6. A run gives 92 percent excess at 0 degrees, then repeats at 40 degrees with the same catalyst. What do you expect?

    • About the same excess, since the helper is unchanged
    • A lower excess, since the minor path gains share
    • No product at all, since heat kills catalysis

  7. Two ligands differ only in the blocking arm. Both runs stay brisk, but ligand B carries the bulkier arm. Which run gives the higher excess, and why?

    • The run with ligand B, since its blocked face climbs higher
    • The run with ligand A, since slim arms react faster
    • Both runs match, since the grip is identical

  8. A student doubles the catalyst amount to raise the excess. What is wrong with the plan?

    • Extra helper flips which face is blocked
    • Extra helper poisons the open face first
    • Extra helper speeds both faces alike, so the gap stays put
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Answer key

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

One face open, one face blocked W1-mt_vFpTH27iHP-s1

  1. True · That split is the whole reason handedness matters for drugs and routes.
  2. How they fit a handed partner in the body · Mirror hands match in bulk facts and differ only in fit with handed partners.
  3. A chiral auxiliary · Catalysts and enzymes let go and repeat, while an auxiliary is cut away after one directed step.
  4. 87.5 · Add and halve: half of 175 is 87.5.
  5. It rises, since the blocked face climbs higher · More crowding lifts the blocked path further, so the open face wins by more.
  6. A lower excess, since the minor path gains share · Warming speeds both paths and shrinks the relative gap, so the excess falls.
  7. The run with ligand B, since its blocked face climbs higher · With pace intact, the bulkier arm widens the gap and the excess follows.
  8. Extra helper speeds both faces alike, so the gap stays put · Amount scales pace, while the excess answers only to the gap between faces.
Worksheet · LightMySky