Unit 25: Multi-Step Synthesis and Retrosynthetic Analysis
Every reaction from the whole course, run in reverse: a target molecule breaking apart, branch by branch, back to the simple pieces it could be built from.
5 topics · 18 questions
Each topic is a path, not a menu: work down it in order and every question builds on the one above. Click any of them to watch the answer draw itself.
Thinking Backward: The Retrosynthetic Arrow
- How it worksHow does an open retrosynthetic arrow mark a target breaking into simpler starting pieces, the reverse of a forward reaction arrow?
- Worked exampleFind one reasonable retrosynthetic disconnection of 2-methyl-2-butanol back to a ketone and a Grignard reagent.
- Common mistakeWhy doesn't a retrosynthetic arrow represent an actual reaction happening inside the flask?
Your turn1 of 2
What is one reasonable retrosynthetic disconnection of 2-methyl-2-butanol back to a ketone and a Grignard reagent?Choosing a Disconnection
- How it worksHow does breaking a bond next to a functional group, where a real reaction could plausibly form it, guide a good disconnection?
- Worked exampleFind two different disconnections of the ester in ethyl benzoate, one at the acyl carbon and one at the alkyl oxygen.
- Common mistakeWhy isn't the shortest-looking disconnection automatically the best one to actually attempt in the lab?
- Going furtherWhat happens to a disconnection choice when the target molecule has more than one functional group competing for attention?
Your turn1 of 2
Ethyl benzoate's ester can be disconnected two different ways: at the acyl carbon, or at the alkyl oxygen. What starting materials does each disconnection trace back to?Functional Group Interconversion in a Synthesis Plan
- How it worksHow does converting an alcohol into a better leaving group, like a tosylate, open up substitution routes that were closed before?
- Worked exampleFind the interconversion needed to turn cyclohexanol into a good SN2 substrate before reacting it with cyanide.
- Going furtherWhat happens to a synthesis plan's length when a target requires several functional group interconversions stacked in a row?
Your turn1 of 2
What interconversion is needed to turn cyclohexanol into a good SN2 substrate before reacting it with cyanide?Protecting Groups in a Multi-Step Synthesis
- How it worksHow does protecting one functional group, like turning a ketone into an acetal, shield it while a reaction targets another part of the molecule?
- Worked exampleFind the sequence of steps needed to add a Grignard reagent to one ketone in a molecule that also carries a second, unprotected ketone.
- Ties togetherHow does this protecting-group strategy connect back to the acetal-as-protecting-group logic from the aldehydes and ketones unit?
Your turn1 of 2
What sequence of steps is needed to add a Grignard reagent to one ketone in a molecule that also carries a second, unprotected ketone?Building a Full Retrosynthetic Tree
- How it worksHow does each disconnection in a retrosynthetic tree generate a new, simpler target that itself gets analyzed all over again?
- Worked exampleFind a full retrosynthetic tree for 3-phenyl-3-pentanol, tracing it back to a ketone plus a Grignard reagent.
- Worked exampleFind a full retrosynthetic tree for benzoic acid, tracing it back to bromobenzene through a Grignard-plus-carbon-dioxide route.
- Common mistakeWhy doesn't a retrosynthetic tree count as finished the moment it reaches any starting material, rather than a genuinely available one?
- Ties togetherHow does building one complete retrosynthetic tree pull together nearly every reaction from the entire course into a single plan?
Your turn1 of 2
A retrosynthetic tree traces a target back through 4 sequential forward steps, each proceeding in 83 percent yield. What is the overall percent yield of the complete forward synthesis?