Cracking ?

Question

1) Why is the simplest alkene ethene, not methene?

2) What is the equation to show the reaction that would occur when propene reacts with bromine.

Answer 1

methene has only one carbon molecule. therefore it cannot double bond with anything.

i assume that you mean reacting with gaseous bromine when you ask about the reaction.

the double bond is attacked by the bromine and bonds to one of the two atoms of the gas. now, with the big, pillowy bromine hanging onto one side, the other bromine cannot add to the same side, thus, the second bromine adds to the opposite side of the initial addition of bromine.

propene starts like this
H...........C-H3
..\........../
.....C=C
.../.......\
H...........H

after one bromine
H.......Br....
..\.......|...
.....C-C-C-H3
.../.......\
H...........H

after the reaction
...H...Br....
....|...|...
H-C-C-CH3
....|...|..
..Br..H

it is a "trans" addition

Answer 2

An alkene is an organic compound with one double bond. Methane is a single carbon compound and it cannot have a double bond.

Bromine adds across a double bond to make a dibromo compound

Br2 + CH3 CH=CH2 -> CH3CHBrCH2Br

You should review your chapter; this is fundamental material and you need to master it to succeed.

Answer 3

An olefin is a compound with a double bond between two carbon atoms. Methane has only one carbon atom. Ethane has two. So ethene (think ethylene), not methene.

CH2=CH-CH3 ===> BrCH2-CH(Br)-CH3