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Alkenes are hydrocarbons that contain at least one carbon-carbon double bond in their structure. This double bond is crucial because it significantly alters the properties of the molecule, making alkenes distinct from their alkane counterparts, which only have single bonds. The double bond is responsible for many of the characteristic reactions that alkenes undergo. Moreover, this double bond is vital for a particular type of isomerism known as cis-trans isomerism (or geometric isomerism).

One of the defining features of this bond is the planar arrangement of the atoms involved. This means that the component atoms, particularly the carbons involved in the double bond and their directly attached groups, lie in the same plane. This arrangement leads to the creation of potential isomers, depending on the spatial orientation of these groups. Thus, the structural attribute of the double bond itself is essential for alkenes to exhibit cis-trans isomerism.

Cycloalkanes are saturated hydrocarbons that have a ring structure. Unlike alkenes, cycloalkanes do not possess double bonds but still can show cis-trans isomerism due to the rigid structure of the ring itself. The ring restricts the rotation of atoms bonded to it, which allows for the possibility of having different spatial arrangements of substituents around the ring.

In cycloalkanes, cis-trans isomerism is determined by the relative positions of substituents attached to the ring. Two substituents on the same side of the cycloalkane form a 'cis' isomer, while those on opposite sides form a 'trans' isomer. The ring’s rigidity, therefore, plays a role similar to that of the double bond in alkenes, in that it prevents free rotation and allows isomerism to occur.

The double bond is a key structural feature in alkenes that allows for restricted rotation, leading to the possibility of cis-trans isomerism. It consists of one sigma bond and one pi bond. The pi bond results from the side-to-side overlap of p orbitals. This pi bond creates an electron cloud above and below the plane of the atoms involved in the double bond.

The electron density in the pi bond prevents the atoms involved in the double bond from rotating freely, unlike in single bonds, where such rotation is possible. This restriction means groups attached to these carbon atoms have fixed spatial relationships, enabling the existence of distinct isomers such as 'cis' and 'trans'. Such isomers are distinguishable by the position of their constituent groups in space relative to the double bond.

Restricted rotation is a fundamental concept that allows both alkenes and cycloalkanes to exhibit cis-trans isomerism. In alkenes, this restriction is due to the presence of a carbon-carbon double bond, where the pi bond portion impedes rotation. The electrons in the pi bond form a cloud that locks the arrangement in place.

In cycloalkanes, restricted rotation stems from the cyclic structure. The atoms within the ring are bound in such a way that they cannot freely rotate around the bonds that connect them in the same manner as linear alkanes. This restriction means the spatial configuration of substituents around the ring is fixed, similar to the effects of a double bond in alkenes. As a result, both alkenes and cycloalkanes can form different isomers based on the arrangements of atoms, manifesting in the characteristic cis-trans isomerism.