One face open, one face blocked

Science · Chemistry · ages 22-23

Name ______________________ Date ____________

In achiral surroundings, mirror-image molecules share every property except how they twist light and fit handed partners.
Circle one: True False
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
Which helper is spent instead of turning over?
- A chiral catalyst that turns over
- An enzyme pocket
- A chiral auxiliary
A reaction gives 75 percent excess. What percent of the product is the major hand?
Answer: ______________
In the taught two-path picture, a ligand keeps its grip but gains a bulkier blocking arm. The blocked climb rises while the open face stays fast, 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
A run gives 92 percent excess at 0 degrees, then repeats at 40 degrees with the same catalyst. In the taught two-path picture, the same two paths keep running and the relative gap shrinks with warmth. 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
Ligand C carries a far bulkier arm, but its run slows to a crawl while ligand B stays brisk. In the two-path picture, what is the consistent reading, and what must you rule out before trusting it?
- The extra bulk likely blocks the open face too, pending a deactivation check
- Bulkier arms always raise both pace and excess
- The catalyst amount was too low to matter
In the taught two-path picture, both paths scale the same way with catalyst amount and no background reaction runs. 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

Answer key

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

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

True · That split is the whole reason handedness matters for drugs and routes.
How they fit a handed partner in the body · Mirror hands match in bulk facts and differ only in fit with handed partners.
A chiral auxiliary · Catalysts and enzymes let go and repeat, while an auxiliary is cut away after one directed step.
87.5 · Add and halve: half of 175 is 87.5.
It rises, since the blocked face climbs higher · The blocked path climbs higher while the open face stays fast, so the open face wins by more.
A lower excess, since the minor path gains share · With the stated gap shrinking, warming speeds both paths and the minor path gains share, so expect a lower excess.
The extra bulk likely blocks the open face too, pending a deactivation check · Over-bulking fits the crawl, but slowness alone cannot prove steric blockage without ruling out deactivation.
Extra helper speeds both faces alike, so the gap stays put · With matched scaling and no background path, amount scales pace for both faces alike, so the gap stays put.