Page 7 - Geometry

Fig 1.6: Position isomerism in C3H6Br2. Functional Group Isomerism In this, the two isomers have two different functional groups. For example, for the molecular formula C3H8O, there have been drawn two structural formulae, as shown in Fig. 7. The one on the left is propan- 1-ol, an alcohol, while that on the right is an ether, named methoxyethane. Fig. 1.7: The two isomers for the molecular formula C3H8O. Stereoisomerism In this form of isomerism, the molecules of the two isomers have the same atoms bonded to each other, but the arrangement of atoms in space is different. It is further divided into two categories, cis-trans isomerism, and optical isomerism. Cis-trans Isomerism While the free rotation around the carbon-carbon single bonds is allowed, it is not allowed for the carbon- carbon double bond. For example, in Fig. 7, the two isomers for 1,2-dibromoethane can be seen. The left one is the cis-isomer, with both the bromine atoms fixed on one side of the double bond. Fig. 7: Cis-trans isomerism. Page 6 of 20 Study Guide for Organic Chemistry