--- title: "Functionalising a Carbon-Hydrogen Bond Without a Handle" description: "Classical routes need a leaving group or a halide already in place. Direct functionalisation works on a carbon-hydrogen bond instead, and the problem becomes selectivity, usually solved by a directing" 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: 2026-09-12 --- > **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 Classical routes need a leaving group or a halide already in place. Direct functionalisation works on a carbon-hydrogen bond instead, and the problem becomes selectivity, usually solved by a directing group that holds the metal near one position. 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 why selectivity, not reactivity, is the hard part when every position carries a similar bond - Predicts which position a stated directing group would activate and draws the metallacycle it forms - Compares a directed route with a route that installs a halide first, on step count and waste - Names a case where sterics rather than a directing group decides the site ## Lesson: Teaching a metal to pick one bond The old way to change a molecule starts from a handle, a leaving group or a halide already in place. Working straight on a carbon hydrogen bond skips that setup. The trouble is that every corner of the molecule carries a similar bond, so choosing the right one is harder than making it react. You can call that choice problem selectivity. **Example.** Picture a ring with an amide group attached. The amide grabs the metal and holds it beside one neighbour position. Metal, group, and ring carbon close into a small ring called a metallacycle, and that neighbour is the position that reacts. You can test the idea: remove the amide and the sharp preference disappears. Compare two plans for the same product. The halide plan installs a halide and then swaps it out, which adds steps and waste: picture five steps against three for the directed plan. The directed plan goes straight at the chosen bond, so it runs shorter and throws away less. When you compare routes, count the steps and weigh the waste. **Tip.** Sometimes bulk wins over direction. A bulky group sitting beside the directing group blocks the near positions, so the metal goes to a farther open site instead. When you see a blocked neighbour staying untouched while a distant site reacts, suspect that crowding, not direction, chose the site. **Recap.** You skip the handle, aim with a directing group, and watch that bulk can overrule the aim. ## Practice 8 questions on this page, each with its working shown. ## Needs first - [Directing Effects in Electrophilic Aromatic Substitution](https://lightmysky.com/learn/science/directing-effects-in-electrophilic-aromatic-substitution-mt_KMRxS6s06f) - [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) ## Opens up - [Olefin Metathesis and Ring-Closing Strategy](https://lightmysky.com/learn/science/olefin-metathesis-and-ring-closing-strategy-mt_J9UAxKsgSk)