22.3 ISOMERS CHAPTER 22 HYDROCARBON COMPOUNDS VOCABULARY TO KNOW Isomers StructuralIsomers Stereoisomers Take out your notes Geometric Isomers and keep track of Trans configuration ALL definitions! Cis configuration Optical Isomers Asymmetric carbon BEFORE WE BEGIN… Remember that all molecules are in reality 3-D! Video showing 3-D molecules- remember molecules are 3-D structures! Photo source: www.wikimedia.og Video source: Rasmol ISOMERS Isomers: Compounds that have the same molecular formula but different molecular structures Different structure = different substance 2 1 2 1 1 2 1 2 1 2 1 2 Photo source: chemguide.co.us STILL CONFUSED? Lets look further into the definition of an isomer (2:40-3:32) Are these molecules isomers STRUCTURAL or are they the same? ISOMERS 1 2 3 4 5 Structural Isomers: compounds that 5 have the same molecular 1 2 3 4 formula, but the atoms are joined together in a different order. 1 2 3 4 Photo source: http://www.slc.ac.nz/WorkshopClub/Workshop/problemsonstructuraliso 5 mers.htm Which has lower STRUCTURAL boiling point? ISOMERS Different physical properties (mp & bp) High number of branches = low boiling point Photo sources: www.lsbu.ac.uk, wikipedia.org STOP AND CREATE! Use your model kits to create 2 structural isomers for C6H4 (there may be more than two options) Photo source: www.kaboodle.com STEREOISOMERS Stereoisomers: Molecules in which the atoms are joined in the same order, but the positions of the atoms in space are different. Two Types: 1. Geometric 2. Optical GEOMETRIC Two Types: ISOMERS 1. Cis-configuration Cis = same side Geometric Isomers: When atoms are joined in the same 2. Trans-configuration order, but differ in their Trans = opposite side orientation of groups around a double bond. Photo source: chemguide.co.us LET’S LOOK INTO THIS A LITTLE DEEPER Still wondering about stererisomers? And what does Cis and Trans mean? (1:30-3:41) WHICH IS THESE IS CIS AND WHICH IS TRANS? Same Side H CH2CH3 Opposite Sides C C (across) H3CCH2 H Photo source: www.uwplatt.edu STOP AND CREATE! Use your model kits to create the Trans-configuration for this molecule: Photo source: www.tennoji-h.oku.ed.jp, www.kaboodle.com OPTICAL ISOMERS Which is Asymmetric? Asymmetric carbon: A carbon with four different atoms or groups attached OPTICAL ISOMERS Optical Isomers: Pairs of molecules that differ only in the way that four different groups are arranged around a central atom. Mirror images! Are these molecules Optical Isomers? Why? CH3CH2CH2 CH3CH2CH2 CH3 CH3 C C CH3CH2 Cl CH3CH2 Cl OPTICAL ISOMERS They are mirror images of each other Take out your mirrors and lets play! Photo source: astrobiology.berkeley.edutures OPTICAL ISOMERS Mirror Images OPTICAL ISOMERS Can not be Superimposed! (no matter how you move them, you can not make them look alike) Try it with your own hands Photo source: www.flicker.com STOP AND CREATE Use your model kits to create an example of an optical isomer & try to superimpose them. Can you? (Remember you must have four different substituents around the carbon atom!) Photo source: www.kaboodle.com REVIEW 1. How can you tell if two compounds are isomers? They have the same molecular formula but different structure 2. What different types of Isomers did we learn about? Structural, Stereoisomers including both Geometric and Optical isomers REVIEW What type of Isomer is this? Geometric: Cis and Trans configurations Photo source: www.chem.purdue.edu REVIEW Draw the optical Isomer REVIEW Is this a Cis or Is this an Trans configuration? asymmetric carbon? Cis configuration Yes, this is asymmetric BEFORE WE MOVE ON… Before we start our lab for this lesson, lets review how to name molecules that have branches (substituent groups). (0:00-2:20) QUICK LAB TIME Structural Isomers of Heptane - Purpose: To build ball-and-stick models and name the eight structural isomers of Heptane (C7H16) Draw structures on paper to keep track of all eight isomers: draw as condensed and line-angle with names Photo source: www.wikimedia.org IN CLASS GROUP PROJECT Working in small groups and using the materials provided: Create a poster outlining the different types of hydrocarbon isomers *Name and define each type and give examples!