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There are three dioxane isomers: 1,2-dioxane, 1,3- dioxane, and 1,4-dioxane. One of these acts like an ether and is an excellent solven for Grignard reactions. Another one is potentially explosive when heated. The third one quickly hydrolyzes in dilute acid. Show which isomer acts like a simple ether, and then explain why one of them is potentially explosive. Propose a mechanism for the acid hydrolysis of the third isomer.

An unknown compound gives the NMR, IR, and mass spectra shown next. Propose a structure, and show how it is consistent with the observed absorptions. Show fragmentations that account for the prominent ion at m/z69 and the smaller peak at m/z99.

Show how you would synthesize each compound from starting materials containing no more than six carbon atoms.

Question: Oxidation of primary alcohol to an aldehyde usually gives some over-oxidation to the carboxylic acid. Assume you have used PCC to oxidize pentan-1-ol to pentanal.

1. Show how you would use acid-base extraction to purify the pentanal.
2. Which of the expected impurities cannot be removed from pentanal by acid-base extractions? How would you remove this impurity?

Question. (A true story.) The chemistry department custodian was cleaning the organic lab when an unmarked bottle fell off a shelf and smashed on the floor, leaving a puddle of volatile liquid. The custodian began to wipe up the puddle, but he was overcome with burning in his eyes and a feeling of having an electric drill thrust up his nose. He left the room and called the fire department, who used breathing equipment to go in and clean up the chemical. Three students were asked to identify the chemical quickly so that the custodian could be treated and chemical could be handled properly. The students took IR and NMR spectra, which follow. The UV spectrum showedat 220 _nm(E= 16,000). The mass spectrometer was down, so no molecular weight was available. Determine the structure of this nasty compound, and show how your structure fits the spectra.

Question:

1. Determine the structure of the carboxylic acid whose proton NMR spectrum appears below.
2. Draw the NMR spectrum you would expect from the corresponding aldehyde whose oxidation gives this carboxylic acid.
3. Point out two distinctive differences in the spectra of the aldehyde and the acid.

Question: Draw all four resonance forms of the fragment at m/z 73 in the mass spectrum of pentanoic acid.