13 - Chapter 13 Introduction to Isomers and Stereochemistry...

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Chapter 13 –Introduction to Isomers and Stereochemistry Our discussion of the alkene addition reactions has ignored an aspect of structure known as stereochemistry. In particular, the alkene addition reactions are capable of yielding structures that differ in subtle but important ways. These different structures are known as stereoisomers. Stereochemistry has to do with the spatial arrangement of atoms within a molecule. It is an aspect of structure that goes beyond bonding connectivity. Before we can discuss the implications of stereochemistry to the alkene addition reaction, we will lay down the basic concepts of stereochemical principles. Be warned that this is a rather lengthy excursion, and it is a detail-oriented topic. Constitutional isomers At the heart of this discussion is a comparison between two structures. The main questions we are asking are (1) are two structures the same or not the same and (2) if they are not the same, then how do they differ? We will eventually provide a chart to systematically determine the answers to these questions, but before doing so, it will be helpful to see some examples. Isomers are two different structures that have the same molecular formula. Constitutional isomers are isomers that differ according to the way the bonds are connected. An example of two different structures that are related as constitutional isomers is n-propanol and iso-propanol. Both have the same molecular formula so they are isomers. Yet, they are obviously not the same. They differ in the way the atoms are connected together. CH 3 CH 2 CH 2 OH OH CHCH 3 CH 3 n-propanol iso-propanol constitutional isomers have the same molecular formula but different bonding connectivity both compounds have the formula C 3 H 8 O Stereoisomers Isomers with the same bonding connectivity but which differ according to how the atoms are arranged in space are called stereoisomers. As it turns out, there are various types of stereoisomers. We will worry about these finer points in a moment, but for now, recognize that
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This note was uploaded on 10/02/2008 for the course CHEM 232 taught by Professor Vanderdonk during the Fall '08 term at University of Illinois at Urbana–Champaign.

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13 - Chapter 13 Introduction to Isomers and Stereochemistry...

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