The names of the cycl Aa△ CHAPTER 4 Cyclic Alkanes t8 stituted cycloalkanes possess stereoisomers carponpmetran eomer /w. 其 tane (not c HC VH Q d-la rat-1- rs but can be inter ted by otations about C-c bonds esesthnersthghoehnpnmnmenpons,and are due to more rid and 1 1 CHAPTER 4 Cyclic Alkanes 4-1 Names and Physical Properties of Cycloalkanes The names of the cycloalkanes follow IUPAC rules. The general formula of a cyclealkane is: CnH2n. To name a cycloalkane, prefix the alkane name with “cyclo”. Numbering a cycloalkane ring is necessary only when there is more than one substituent. In nonsubstituted cycloalkanes, the attached carbon is numbered number 1. Use the lowest possible numbering sequence for polysubstituted cycloalkanes. If two identical numbering sequences are possible, use alphabetical precedence. Substituted cycloalkanes are sometimes named as cycloalkyl derivatives. The smaller unit is generally treated as a substituent to the larger unit. •Propylcyclopentane (not cyclopentylpropane) •Cyclohexyloctane (not octylcyclohexane) Disubstituted cycloalkanes possess stereoisomers. Disubstituted cycloalkanes having substituents on different carbons possess cis (same side) / trans (opposite side) isomers. Cis/trans isomers are examples of stereoisomers. These are non￾superimposable molecules having the same molecular formula and connectivity. Conformers are also stereoisomers but can be interconverted by rotations about C-C bonds. The properties of the cycloalkanes differ from those of their straight chain analogs. Cycloalkanes have higher boiling points, melting points, and densities than their straight-chain analogs. •Increased London forces are due to more rigid and symmetric cyclic systems. The smaller cycloalkanes with an odd number of carbon atoms have lower melting points than expected compared to cycloalkanes with an even number of carbon atoms. This is attributed to crystal-packing forces between the two types of cycloalkanes