Question

How many different alkenes can be hydrogenated to form hexane?

Answer 1

Three different alkenes can be hydrogenated to form hexane.

You want a 6-carbon alkane, so you start with a 6-carbon alkene.

The possibilities are:

hex-1-ene, CH₃CH₂CH₂CH₂CH=CH₂
hex-2-ene, CH₃CH₂CH₂CH=CHCH₃
hex-3-ene, CH₃CH₂CH=CHCH₂CH₃

You can react any of these with hydrogen and a nickel catalyst.

The equations are

CH₃CH₂CH₂CH₂CH=CH₂ + H₂ → CH₃CH₂CH₂CH₂CH₂CH₃

CH₃CH₂CH₂CH=CHCH₃ + H₂ → CH₃CH₂CH₂CH₂CH₂CH₃

CH₃CH₂CH=CHCH₂CH₃ + H₂ → CH₃CH₂CH₂CH₂CH₂CH₃

There are also alkadienes and -trienes, that have more than one double bond. Just one example:

hex-1,3-diene, CH₃CH₂CH=CH₂CH=CH₂