ISSUE:

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Hello Forero, your product is the one seen in the figure below, the key is in the CH2 bound to oxygen that is seen at 4.2 ppm and in the isolated CH2 at 3.4 ppm; In the infrared we observed 2 strong carbonyl signals at 1715 and 1745 respectively, I leave the rest of the analysis to you.


Greetings

Two problems that I would like you to help me with.

The first is using the appropriate reagents and sequence of reactions, propose how
2-Methyl-1,4-pentadiene could be obtained from Acetaldehyde.

The second problem is that I need to order these compounds according to their reactivity against HCN.

Hello forum member,
regarding the reactivity of HCN against aliphatic carbonyl compounds, the steric hindrance has a great influence.
An aldehyde reacts faster than a ketone. In aromatic carbonyl compounds, it influences the electron-withdrawing or electron-donating substituents and their ppositions. Thinking that the ketone forms an intermediate with a positive charge, an electron donor would stabilize said charge and make the reaction faster. Regarding the synthesis, it would be to convert the acetaldehyde into pent-4-en-2-one by the dithian method, and then make it react with Wittig's reagent. Another route is to react the acetaldehyde with the appropriate Grignard reagent and then do a Hoffman elimination with the most hindered base for more yield.