How can I draw all the isomers with molecular formula #C_6H_12# ? (that contain a cyclobutane ring and there are seven) and how can I Identify chiral compounds and achiral compounds?
1 Answer
You identify chiral and achiral compounds by looking for internal mirror image planes.
You know that you have a cyclobutane ring.
That leaves two extra carbon atoms. They could be an ethyl group or two methyl groups.
Start by drawing ethylcyclobutane.
This compound is achiral because there is an internal mirror plane.
Next we put a methyl group on C-1 and then put the other methyl group in every possible location.
This gives us 1,1-dimethylcyclobutane.
This compound is achiral because there is a mirror plane perpendicular to the ring and passing through C-1 and C-3.
cis-1,2-Dimethylcyclobutane
This compound is achiral because there is a mirror plane perpendicular to the ring and passing through the midpoints of the C1-C2 and C3-C4 bonds.
trans-1,2-Dimethylcyclobutane
This compound is chiral because there is no mirror plane.
It exists as a pair of enantiomers:
cis-1,3-Dimethylcyclobutane
This compound is achiral because there is a mirror plane perpendicular to the ring and passing through C-1 and C-3.
trans-1,3-Dimethylcyclobutane
This compound is achiral because there is a mirror plane perpendicular to the ring and passing through C-1 and C-3.
And we have drawn the seven cyclobutane isomers with formula
