Question

Question #cd21d

Answer 1

The main product is propyne, and the minor product is propadiene.

This is an `"E2"` elimination that occurs in stages.

The product of the first elimination is 2-chloropropene.

`"CH"_3"CCl"_2"CH"_3 stackrel(color(blue)("-HCl"))→ "CH"_3"CCl=CH"_2`

For the second step, we can eliminate the β-hydrogen at either `"C-1"` or `"C-3"`.

If we eliminate the `"H"` at `"C-1"`, the product is propyne.

`"CH"_3"CCl=CH"_2 stackrel(color(blue)("-HCl"))→ "CH"_3"C≡CH"`

If we eliminate the `"H"` at `"C-3"`, the product is propadiene.

`"CH"_3"CCl=CH"_2 stackrel(color(blue)("-HCl"))→ "CH"_2"=C=CH"_2`

Alkynes are more stable than 1,2-dienes, so the major product is propyne.

I would expect the two products to form in about a 2:1 ratio, because a commercial product called MAPP gas contains the two gases in that proportion.