Take the name apart: The stem is but- so it has four carbons. It's cyclic, so these four carbons must be in a ring structure. To be a cis isomer, it must be an alkene. The carbons of the double bond must have the lowest numbers. The two chlorine atoms are on these lowest numbers, 1 and 2. The way they are arranged in space is determined by whether the compound is cis or trans.
Take the name apart: The stem is but- so it has four carbons. It's cyclic, so these four carbons must be in a ring structure. To be a cis isomer, it must be an alkene. The carbons of the double bond must have the lowest numbers. The two chlorine atoms are on these lowest numbers, 1 and 2. The way they are arranged in space is determined by whether the compound is cis or trans.
Spoiler
It is possible for cycloalkanes to be stereoisomers. It requires a restricted bond. In a cycloalkane you cannot rotate the bonds such that you reposition the arrangement of chlorine atoms.
It is possible for cycloalkanes to be stereoisomers. It requires a restricted bond. In a cycloalkane you cannot rotate the bonds such that you reposition the arrangement of chlorine atoms.
Ahh good point. I'd forgotten that, generally we see cis/trans isomers of alkenes. Thanks for correcting me!