How many isomers of C4H6O are there?

Answer 1

Without more information, specifically some IR and/or NMR data, it is difficult to predict the exact structure of the compound. However, based on only the formula, we need to first determine the degrees of unsaturation using the formula:

DoU = (2C + 2 - H) / 2 = (2 x 4 + 2 - 6) / 2 = (8 + 2 - 6) / 2 = (4) / 2 = 2

The degrees of unsaturation can tell us whether the molecule has multiple bonds (double or triple) or a combination of a cyclic ring + a multiple bond.

For the above chemical formula, a DoU value of 2 means that the structure can contain either:

1) 2 double bonds

2) 1 triple bond

3) 1 double bond + 1 cyclic ring

As a result, without more information, I can derive structures that fit the above 3 scenarios. For instance, a structure for option 1) can be:

H₂C=CH-CH₂-CH=O (2nd isomer: H₃C-CH=CH-CH=O)

Option 2)

H₃C-C≡C-CH₂-OH (2nd isomer: HC≡C-CH₂CH₂-OH, 3rd isomer: H₃C-CH₂-C≡C-OH)

**This molecule contains a triple bond, but its DoU = 2!

Option 3)

I am unable to draw the last structure because wyzant does not provide a chemdraw option in this forum and this last structure contains a cyclic ring. However, you can google the structure of a compound called "furan." Furan is a 5-membered cyclic ring with 2 double bonds. Remove 1 of the double bonds from the structure of furan, and you get a molecule with the chemical formula C₄H₆O. For this structure, you can draw 2 isomers (draw resonance structures by moving the double bond).

As a result, you can see that you are able to obtain at least 7 isomers thus far from the above chemical formula.