MediumChemistryHigh School (11–12)Organic Compounds with Functional Groups › Aldehydes, Ketones and Carboxylic AcidsNumerical
A route finder has the arrows of a table of reactions…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A route finder has the arrows of a table of reactions. It is asked for a route from an alkyl halide to an aldehyde, and from a primary alcohol to an acyl chloride. Find the number of steps and the carbons added in the first route. Name both reagents of the first route. How many steps does the second route need?
Need a reminder? The key ideaShow
Work backwards from the target and count the carbons first. Cyanide and RMgX with CO add one carbon, an aldol joins two molecules, and soda lime or the haloform reaction removes one. The overall yield of a route is the product of the step yields. The degree of unsaturation is . The tests are 2,4-DNP (any aldehyde or ketone), Tollens (aldehydes), Fehling (aliphatic aldehydes) and iodoform (CHCO-).
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. First route. The alkyl halide reacts with potassium cyanide to give a nitrile. DIBAL-H, then water, turns the nitrile into the aldehyde. That is 2 steps.
Step 2. Carbons. The cyanide adds one carbon. The second step adds none. So the carbons added are 1.
Step 3. Second route. The alcohol is oxidised to an aldehyde with PCC, then to an acid with permanganate, then turned into the acyl chloride with thionyl chloride. That is 3 steps.
Answer: 2 steps and 1 carbon, with KCN and DIBAL-H; the second route takes 3 steps.
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