Teaching a metal to pick one bond

Science · Chemistry · ages 23-24

Name ______________________ Date ____________

For N,N-dimethylbenzamide numbered as in the lesson, which pair of equivalent sites does the stated O-bound ortho-activation model predict will undergo activation?
- C3 and C5, the two meta sites on the ring
- C2 and C6, the two ortho sites on the ring
- C1 and C4, the ipso and para sites on the ring
Why can site selection be difficult when several C-H bonds can react under the chosen conditions?
- Several sites can compete to give different products
- Every C-H bond has exactly the same chemical environment
- No C-H bond can react with any catalyst under any conditions
An aryl-halide cross-coupling starts from an installed C-X bond, while direct C-H functionalisation can avoid installing that bond first.
Circle one: True False
For the same product and accounting boundary, a halide-first route makes 9 kg waste per kg product and a directed route makes 4 kg. Which measured result favours the directed route?
- Directed: 4 kg waste/kg product
- Halide-first: 9 kg waste/kg product
- Both routes together: 13 kg waste/kg product
In the stated O-bound benzamide model, which closed path includes metal M, the carbonyl group, arene C1 and ortho carbon C2?
- M-O-C(carbonyl)-C1-M, a four-membered ring
- M-O-C(carbonyl)-C1-C2-C3-M, a six-membered ring
- M-O-C(carbonyl)-C1-C2-M, a five-membered ring
A halide-first route needs 5 steps and a directed route needs 3 steps for the same product. How many steps does the directed route save?
Answer: ______________
Replacing an amide with a nonbinding analogue reduces ortho preference under matched conditions. What conclusion is justified?
- This proves coordination is the only possible source of selectivity
- This supports coordination, but other changes may matter
- This proves steric and electronic changes cannot affect the reaction
In a stated nondirected iridium-catalysed arene borylation model, sterics control site choice. C2 has two bulky neighbours, C4 has one and C5 has none. Which candidate site does this model favour?
- C2, between two bulky neighbours
- C4, beside one bulky neighbour
- C5, with no bulky neighbours

Answer key

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

Teaching a metal to pick one bond W1-mt_j0LaIeS2VP-s1

C2 and C6, the two ortho sites on the ring · The model reaches C2 or C6 through equivalent five-membered metallacycles. C3 and C5 are also equivalent to each other, but are not its predicted activation sites.
Several sites can compete to give different products · Different reactive sites can give different positional products. Selectivity depends on how the chosen system distinguishes them.
True · This compares two route types. It does not say that every classical reaction requires a halide or leaving group.
Directed: 4 kg waste/kg product · The directed route has the lower measured waste ratio, 4 rather than 9 kg/kg. The conclusion follows from the data, not the route label.
M-O-C(carbonyl)-C1-C2-M, a five-membered ring · The five distinct atoms are M, O, the carbonyl carbon, C1 and C2. Returning to M closes the ring.
2 · Subtract 3 from 5: the directed route saves 2 steps. Step count alone does not determine waste.
This supports coordination, but other changes may matter · The control supports a coordination hypothesis, but replacement also changes electronics and sterics. Further evidence is needed for an exclusive assignment.
C5, with no bulky neighbours · The stated steric-control model favours the least crowded candidate, C5. It does not imply that every blocked directed reaction moves remotely.