You have four bottles, each containing one of the four compounds shown below, E,

ID: 959491 • Letter: Y

Question

You have four bottles, each containing one of the four compounds shown below, E, F, G, and H. From the spectral data given, determine which bottle holds which compound. All compounds have signals in the aromatic region of the NMR for 4H, so that information is of no use. Bottle 1: IR 1720 cm^-1 1H NMR: delta 1.38 (t, 3H), 2.40 (s, 3H), 4.36 (q, 2H) Bottle 2: IR 1688, cm^-1 1H NMR: delta 1.12 (t, 3H), 2.81 (q, 2H), 3.76 (s, 3H) Bottle 3: IR 1725 cm^-1 1H NMR: delta 1.21 (t, 3H), 2.65 (q, 2H), 3.85 (s, 3H) Bottle 4: IR 1680 cm^-1 1H NMR: delta 1.40 (t, 3H), 2.50 (s, 3H), 4.07 (q, 2H)

Explanation / Answer

Hi, remember first that the IR frequency for an ester group is higher than that of a ketone group. Since, E is an ester, it must be either in bottle 1 or bottle 3 since they have higher frequencies of carbonyl group.

Note: 2H, 3H and 4H are the integration values corresponding to the number of hydrogen atoms generating a signal.

Now look at the structure of E, it has a CH2 group next to an O and CH3 so it must be a downfield quartet. See the value of 2H quartet in bottle 1. It concurs with the structure of E. 3H triplet at 1.38 is the methyl group attached to the ring, 2H quartet at 4.36 is the CH2 group while 3H singlet at 2.40 is the methyl carbon of alkyl chain (ethyl).

since, G is also an ester, it must be in bottle 3 matching with the IR frequency of the ester carbonyl group. 3H triplet at 1.21 is the methyl group of alkyl chain, while 2H quartet at 2.65 is the CH2 group next attached to the ring.Finally 3H singlet at 3.85 is the methyl group attached to oxygen.

F is in bottle 2. 3H triplet at 1.12 is the methyl group of the chain, 2H quartet ar 2.81 is the CH2 group attached to the carbonyl group while a 3H singlet at 3.76 is the methyl group attached to oxygen. The electronegativity of the oxygen atom makes this single appear downfield.

Finally bottle 4 is H.

3H singlet at 2.50 is the methyl group next to the carbonly group. 2H quartet at 4.07 is the CH2 group attached to oxygen while 3H triplet at 1.40 is the methyl group attached to the CH2 group.

I hope it is helpful to you.

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You have four bottles, each containing one of the four compounds shown below, E,

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