Emily characterized an unknown compound A, with molecular formula C4HgO, using 1

Question

Emily characterized an unknown compound A, with molecular formula C4HgO, using 1H NMR, see below. Compound A gave a positive Tollens test. A was reacted with Wittig reagent shown and after an aqueous workup, Michael isolated a new compound B Hydrogenation of B in ethanol gave a new compound C, which displayed an NMR spectra shown on the next page. Draw the structures of each compound (A-C) and explain your answer using the spectral experimental and spectroscopic clues given. PPh3 H3C THF H2/Pd Proton NMR of compound A: doublet int. = 6 H doublet int 1 H multiplet int.= 1 H 10 4 2 0 PPM 1. Assign the Structure of compound A: Analysis of 1H NMR spectra: Type of H shift (ppm)integration splitting tentative identification Proton NMR of compound B: integration numbers given. singlet int = 3H doublet int = 6H doublet doublet int 2H doublet int = 2H quartet (can you guess why?) int- 1H ss why?) multiplet int- 1H 8 4 PPM 2 0

Explanation / Answer

If the compound give results for tollens reagent then it will be aldehyde or ketone. from the first nmr we know that there will be 6 protons in the same environment that is attached to the same carbon , two methyl with same carbon.the doublet is for carbonyl. with the help of molecular formula we can predict the structure should be Isobutyraldehyde.

then reacion with wittig reagent shown above give the product containing para methyl benzene group it shows from the aromatic region signals from spectrum 2.

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