cycloalkanes and cistrans isomerism?

Question

what structural feature of cycloalkanes makes cistrans isomerism in them possible?

Answer 1

The C to C bonds are single bonds. That means the atoms can rotate around the bonds, which isn't possible with double or triple bonds in cyclic structures. In linear structures, double bonds could rotate.
You have to imagine a 3-D image. Try cyclooctane. It can either be flat and look like a stop sign (cis bonds), or you can rotate one of the C molecules, and the molecule would twist around, more like a platelet.

Answer 2

The fact that they are tied around in a tight circle. That makes possible the choices of cis ("up-up") and trans ("up-down"). Just as one cannot "undo" a double bond to reverse cis and trans, so one cannot (under ordinary circumstances) take apart a ring to rearrange the up-or-down geometries of substituents.