How many isomers are there of butanal?
You have to remember that butanal is an aldehyde, a group that only exists on terminal atoms. Thus, the aldehyde group can only go on the terminal carbons. There are only two isomers, and they are 1-butanal and 2-methylpropanal.
"3-methylpropanal" is identical to 1-butanal.
"2-butanone" is not an aldehyde anymore, but a ketone.
The isomers should be:
I just moved the methyl group inwards as much as possible. You can see that the aldehyde group in 2-methylpropanal can then be moved around the outer carbon, but since there is rotational symmetry, it turns out to be the same isomer.
Thus, there are only two (straight-chained) isomers total that are also aldehydes.
If you are not restricting yourself to only aldehydes, i.e. if you are looking for isomers of
2-butanone would work, and so would crotyl alcohol, cyclobutanol, 2-methoxypropene, and tetrahydrofuran.
That would total seven.
You can find their structures in the link above (except for cyclobutanol, which is just a four-membered ring with an
There are many isomers of butanal.
Including butanal, there are three carbonyl-containing isomers. These are
In addition there are many unsaturated and cyclic alcohols as well as unsaturated and cyclic ethers (too many to draw here).