Try it on paper first. A hint, the key idea and the worked solution are here when you need them.
The three ethers of formula are methoxypropane, ethoxyethane and 2-methoxypropane. Each is heated separately with an excess of hydrogen iodide until no alcohol is left. Find the total number of different alkyl iodides obtained from the three, counting each iodide once. Then find how many moles of HI one mole of ethoxyethane uses, and how many moles of HI one mole of 2-methoxypropane uses.
HI cleaves the C-O bond. Iodide attacks the less crowded carbon (or the tertiary one). An aryl C-O bond stays, so an aryl alkyl ether gives a phenol and an alkyl iodide. Excess HI turns an alkyl ether into two alkyl iodides. The net dipole of two bond dipoles at angle is .
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Given. Three ethers and excess HI.
Step 1. Methoxypropane. Iodide attacks the methyl carbon, which is less crowded than a CH of the propyl group, giving iodomethane and propan-1-ol. Excess HI converts the propan-1-ol to 1-iodopropane. Iodides: iodomethane and 1-iodopropane.
Step 2. Ethoxyethane. The two groups are alike. The products are ethanol, then iodoethane. Iodide: iodoethane.
Step 3. 2-Methoxypropane. Iodide attacks the methyl carbon, not the secondary carbon. The products are iodomethane and propan-2-ol, and the alcohol then gives 2-iodopropane. Iodides: iodomethane and 2-iodopropane.
Step 4. Count. The different iodides are iodomethane, 1-iodopropane, iodoethane and 2-iodopropane: 4.
Step 5. HI used. Each ether uses one HI for the first cleavage and one for the alcohol: 2 each, for a total of 2 moles per mole.
Check. Each reaction gives two iodide molecules and one water: .
Answer: 4, 2 and 2.
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