[rjt027]

This homework assignment wants me to chose a single constitutional isomer of cis-1,2-dimethylcyclobutane.

Options are:
    a.    cis-1,2-Dimethylcyclopropane
    b.   trans-1,2-Dimethylcyclopropane
    c.   1,1-Dimethylcyclobutane
    d.   trans-1,2-Dimethylcyclobutane
    e.   2,2-Dimethylbutane

Constitutional Isomer = Same chemical formula but different order of connections between the atoms....

A & B are obviously wrong, E is not cyclic

C & D are both Isomers of cis-1,2-dimethylcyclobutane.

What is the deciding factor, what am I missing?

Thank you guys for your help.
-Rob

[discodermolide]

Quote "Constitutional Isomer = Same chemical formula but different order of connections between the atoms."
What's the difference between c & d? Is there a difference and does it fit the definition.

[rjt027]

C: Both CH3 groups are attached to carbon #1
D: One CH3 is attached on Carbon #1 while One CH3 group is attached to the Carbon #2 (attached opposite in rotation to the first CH3)

They both have the exact same formula.
C: Has a different ORDER of connections. (The 2nd methyl group is attached to C1 instead of C2)
D: Same chemical structure and bonding order, but different 3D orientation.

Curious though in how to answer a question that wants only ONE constitutional isomer.

[discodermolide]

So D has the same connection order!
And the answer is?