14 - Chapter 14 Stereochemistry and Reactivity: New...

Info iconThis preview shows pages 1–4. Sign up to view the full content.

View Full Document Right Arrow Icon
Chapter 14 – Stereochemistry and Reactivity: New Mechanistic Insight Here we will further continue our excursion into stereochemistry and then return to our discussion of alkene addition reactions. Now that our analysis of a reaction can include the three-dimensional arrangement of atoms is space, we can gain new insight into the reaction mechanism. This higher level of analysis will bring deeper understanding as to pathway that the reaction follows. A flow chart to determine isomeric relationships The flow chart below provides us with an isomeric classification scheme for a pair of structures having the same formula. Let’s put the flow chart to work with some examples. As usual, it is best to work through these examples by constructing physical models. a pair of structures w/ the same formula same connectivity? yes no superimposable? yes no related as mirror images? yes no constitutional isomers structures are one and the same stereoisomers enantiomers diastereomers Example 1 – Two representations of the same structure Building physical models and manipulating them in your hands will greatly facilitate this discussion. Our first example is a pair of structures that are two different representations of the same thing. After realizing that the two structures have the same pattern of bonding connectivity, rotate them, and translate them through space until you find a way that they can be superimposed directly on one another, atom-for-atom. Follow the flow chart (the path with the green highlighted boxes) and see how it leads us to determine that these structures are one and the same. It is possible to represent two structures in many different ways. It is important to be able to examine a pair to see if they are the same, or not the same.
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Example 2 – A Diastereomeric Pair The pair of structures below has the same connectivity; yet, it is impossible to superimpose each atom of the first structure onto each atom of the second structure, therefore these structures are stereoisomers. It remains for us to decide whether or not they are mirror images of one another. Because the methyl groups are oriented in opposite directions for the first structure, but in the same direction for the second, they cannot be related by a mirror plane, therefore, these stereoisomers are diastereomers. Example 3 – A Diastereomeric Pair In the third example, methyl groups within each structure are oriented in opposite directions, however, it is not possible to superimpose one structure on the other, so again, we are faced with a set of stereoisomers. Visualization in this case may require that you make models
Background image of page 2
of each structure and try to bring them together, atom-for-atom. Once you convince yourself that the structures are stereoisomers, next determine if they are related as mirror images. For this purpose, the structures can be rotated or translated through space in any way possible. By rotation of one structure by 1/5 of a turn, it is possible to see how reflection through a plane
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 4
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 9

14 - Chapter 14 Stereochemistry and Reactivity: New...

This preview shows document pages 1 - 4. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online