--- title: "Functionalising a Carbon-Hydrogen Bond Without a Handle" description: "Direct C-H functionalisation can avoid installing a carbon-halogen bond before coupling. Reactivity and site selectivity both matter. Some catalysts use coordinating directing groups; other systems fa" canonical: https://lightmysky.com/learn/science/functionalising-a-carbon-hydrogen-bond-without-a-handle-mt_j0LaIeS2VP source: https://lightmysky.com/learn/science/functionalising-a-carbon-hydrogen-bond-without-a-handle-mt_j0LaIeS2VP.md retrieved: 2026-11-12 --- > **Agent view.** This is the Markdown twin of the page, for tools and assistants. > When to use this site, and the call that answers each job: https://lightmysky.com/agent-instructions.md > API description (OpenAPI 3.1): https://lightmysky.com/openapi.json · Authentication: https://lightmysky.com/auth.md > Pricing: https://lightmysky.com/pricing.md · Catalog: https://lightmysky.com/llms.txt · Full catalog: https://lightmysky.com/llms-full.txt > Every machine-readable file on this domain: https://lightmysky.com/.well-known/ai-catalog.json > Ask for Markdown with `Accept: text/markdown`, a `.md` address, or `?mode=agent`. # Functionalising a Carbon-Hydrogen Bond Without a Handle Direct C-H functionalisation can avoid installing a carbon-halogen bond before coupling. Reactivity and site selectivity both matter. Some catalysts use coordinating directing groups; other systems favour less crowded sites. Compare step count and waste for the actual routes. Subject: Science · Area: Chemistry · Ages 23 to 24 Page: https://lightmysky.com/learn/science/functionalising-a-carbon-hydrogen-bond-without-a-handle-mt_j0LaIeS2VP ## Ready when they can - Explains how reactivity and site selectivity constrain direct C-H functionalisation - Predicts ortho activation in a stated benzamide coordination model and traces its five-membered metallacycle - Compares a directed route and a halide-first route using step counts and measured waste - Explains least-crowded-site selection in a stated nondirected arene borylation model ## Lesson: Teaching a metal to pick one bond Many cross-couplings start from a carbon-halogen bond installed beforehand. Direct C-H functionalisation can avoid that operation, but not all classical reactions require such a handle. Reactivity and site selectivity both matter. Several C-H sites may compete, and their electronic and steric environments can differ. State the catalyst and conditions before predicting a site. Use an O-bound ortho-activation model for N,N-dimethylbenzamide. Number its arene carbons C1 to C6 around the ring; C1 bears C(=O)N(CH3)2. Oxygen coordination gives the five-membered path M-O-C(carbonyl)-C1-C2-M. Activation at C6 gives an equivalent path. The model predicts activation at accessible ortho sites C2 and C6, not at the equivalent meta sites C3 and C5. This is not a rule for every amide or catalyst. Compare complete routes, including directing-group installation and removal. A four-step route saves two operations compared with a six-step route. Fewer steps do not prove less waste. Compare measured waste per amount of product using the same boundary, including solvent, reagents, catalysts and work-up. Waste of 6 versus 4 kg per kilogram of product favours the latter on that metric. *(drawing: These bars compare step counts. They do not measure waste or show molecular structures.)* Many nondirected iridium-catalysed arene borylations favour less crowded C-H sites. In a stated steric-control model, compare bulky neighbours around candidate sites. This differs from coordination-directed activation. Blocking directed ortho sites may suppress reaction or change selectivity; it does not automatically cause reaction at a distant site. Test a directing-group hypothesis with controls. Compare the original substrate with a nonbinding analogue under matched conditions, measuring conversion and site ratios. Loss of ortho preference supports a role for coordination. Replacement also changes electronics and sterics, so additional controls or mechanistic evidence are needed before assigning the effect exclusively to binding. **Recap.** Predict sites from a stated catalytic model. Distinguish coordination from steric control, compare complete routes, and test directing-group claims with controls. *Original lesson, questions and flashcard revisions written for this dataset.* ## Practice 8 questions on this page, each with its working shown. ## Needs first - [Cross-Coupling in Practice: Choosing Ligand, Base and Conditions](https://lightmysky.com/learn/science/cross-coupling-in-practice-choosing-ligand-base-and-conditions-mt_y2vF6EDb2X) ## Optional connections - [Directing Effects in Electrophilic Aromatic Substitution](https://lightmysky.com/learn/science/directing-effects-in-electrophilic-aromatic-substitution-mt_KMRxS6s06f) ## Opens up - [Olefin Metathesis and Ring-Closing Strategy](https://lightmysky.com/learn/science/olefin-metathesis-and-ring-closing-strategy-mt_J9UAxKsgSk)