Hydrocarbons have different structures but the same atoms

[chawki]

Homework Statement

The following hydrocarbons have different structures but the same atoms except for one. Which of them is this exception and what is the difference?
a)cyclobutane
b)1-butene
c)2-butene
d)cyclobutene
e)methylcyclopropane

Homework Equations

Which of them is this exception and what is the difference?

The Attempt at a Solution

At a first glance, i would say (a)

 

[zhermes]

Why don't you take a second glance and draw out the structure/chemical-formulae to find out.

 

[chawki]

ok, i think it's (d) with the formula C4H6

 

[zhermes]

Looks good, 'd' has 2 degrees of unsaturation---the cycle and the double bond.