Help with IR spectroscopy problem?

[zyzzbruh]

Q: A hydrocarbon "Z" has a molecular formula of C6H8. Z does not react with Li/NH3 but does react with H2/Pd. Z yields a SINGLE product on ozonolysis. The product of ozonolysis exhibits IR signals at 2900, 2700, 1725 and two triplets in hydrogen NMR.

So, I gathered that the product will have C-H bonds, an aldehyde and ketone. The IHD is 3, so I'm assuming it is just a ring with two double bonds.

I just can't seem to work out a "Z" in this scenario which yields a single product that satisfies the criteria above.

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[theonlytycrane]

units of unsaturation: 3

ozonolysis gives a single product so it has to be cyclic.

cyclohexyne? (https://pubchem.ncbi.nlm.nih.gov/compound/11079373#section=Top)

 

[edgerock24]

This is definitely not something you'd see on the MCAT.

 

[aldol16]

cyclohexyne? (https://pubchem.ncbi.nlm.nih.gov/compound/11079373#section=Top)

I think it's unlikely to be an alkyne because Li/NH3 reduces alkynes and alkynes only. Since it reacts with Pd/H2, it must be an alkene. Given the molecular formula, it's likely to be a benzene with one alkene fully reduced (cyclohexadiene). You're right that it must be cyclic because it only yields one product on ozonolysis.

The IR stretch at 2700 is likely the aldehyde C-H bond whereas the one at 1725 corresponds to the carbonyl. The one at 2900 is likely just the alkane C-H bonds. The only problem is that if you draw the cyclohexadiene where the double bonds are on opposite sides of the ring, you only get 1 triplet on the NMR because the alkene protons could be equivalent.

 

[7331poas]

cyclohexadiene would yield more than 1 product

 

[aldol16]

cyclohexadiene would yield more than 1 product

Depends on whether you can control how much ozone is added and the relative reactivity of the second alkene once you have a di-aldehyde. The molecule clearly has more than one degree of desaturation and it's not an alkyne because it doesn't react with Li/NH3. Do you have a proposal?