Cycloalkanes

Compounds that contain rings of carbon atoms Have the general formula C n H 2n Represented by polygons in skeletal drawings cyclopropanecyclobutane cyclopentane

Naming cycloalkanes 1.Count the number of carbon atoms in the ring and the number in the largest substituent. –If the number of carbon atoms in the ring is equal to or greater than the number in the largest substituent, the compound is named as alkyl-substituted cycloalkane.

Substituted cycloalkane Methylcyclopentane Cycloalkyl-substituted alkane 3 carbons4 carbons 1-cyclopropylbutane

For alkyl-substituted cycloalkanes, start at a point of attachment and number the substituents on the ring so as to arrive at the lowest sum. 1,3-dimethylcyclohexane NOT 1,5-dimethylcyclohexane

3.When two or more different alkyl groups or halogens are present, number them by alphabetical priority. CH 3 CH 2 CH 3 1-ethyl-2-methylcyclopentane NOT 2-ethyl-1-methylcyclopentane

Cis-trans isomers Because there is not free rotation in cycloalkanes, geometric isomers called stereoisomers are formed. Cis (L. “on the same side”) Trans (L. “across from”) Geometric isomers do not convert back and forth.

H H H H H Cl H H Cl H H H Cl H H Cl H H trans-1,4-dichlorocyclohexane cis-1,4-dichlorocyclohexane

Chair Conformation

Homework Page 320: 39-43