Dehydrohalogenation

Question 1

purpose

Answer 1

form alkyne from a geminal or vicinal dihalide

Question 2

geminal definition

Answer 2

2 attached to the same carbon

Question 3

vicinal definition

Answer 3

attached to different carbons

Question 4

this reaction is similar to

Answer 4

alkyl halide elimination to form alkenes (E2)

Question 5

need?

Answer 5

very basic conditions

excess base to get the 2nd dehydrohalogenation

Question 6

strong bases typically used

Answer 6

KOH at 200ºC (potassium hydroxide)

NaNH2 at 150ºC (sodium azide) stronger base than OH-

RO- (t-buO- K+, DMSO, heat)

Question 7

if using NaNH2 to produce a terminal alkyne you need

Answer 7

an aqueous (H2O NOT H3O+) workup step

Question 8

mechanism

Answer 8

E2 two times

Question 9

what if more than 1 possible beta-hydrogen?

Answer 9

get a mixture of alkyne and possible allene

Question 10

allene definition

Answer 10

two double bonds adjacent to eachother (not conjugated) so pi bonds are perpendicular and not as stable

Question 11

synthetic way to make alkynes

Answer 11

alkene + X2 —> dihalide + strong base (excess) —> alkyne