Question #cd21d

1 Answer
May 14, 2015

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.