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Lecture | =Chem3x11 Lecture 1= | ||
Key concepts | This lecture is an overview of isomerism, then some material on stereocentres and what chiral molecules look like in <sup>1</sup>H NMR spectroscopy. | ||
==Key concepts== | |||
* There are two different kinds of stereoisomers | * There are two different kinds of stereoisomers | ||
* Conformations of alkanes governed by sterics and electronics | * Conformations of alkanes governed by sterics and electronics | ||
* Prochiral centres become interesting in a chiral environment | * Prochiral centres become interesting in a chiral environment | ||
==Kinds of Isomerism== | |||
Constitutional isomers are the easiest to think about. The molecule is put together differently. If you interviewed each atom in turn, and asked which other atoms they are bonded to, the answers would differ for constitutional isomers. Atoms in stereoisomers would give you the same answer since the atoms are connected to each other the same, only the positions of the atoms in space changes. The easiest kind of stereoisomers to conceptualize are those around a double bond, i.e. ''E''- and ''Z''- isomers. To interconvert these you'd need to break the double bond, and when a bond needs to be broken we call that Configurational Isomerism. Stereocentres are like that too, so enantiomers are configurational isomers. Conformational isomers are different - still stereoisomers, but it's possible to interconvert them without breaking anything, usually by rotation around a single bond. The example below concerns alkanes, which seems silly because we never isolate the alkane isomers under normal conditions - the bond rotation is too easy/fast. But there are some very interesting and important examples of this kind of isomerism, particularly in Nature. | Constitutional isomers are the easiest to think about. The molecule is put together differently. If you interviewed each atom in turn, and asked which other atoms they are bonded to, the answers would differ for constitutional isomers. Atoms in stereoisomers would give you the same answer since the atoms are connected to each other the same, only the positions of the atoms in space changes. The easiest kind of stereoisomers to conceptualize are those around a double bond, i.e. ''E''- and ''Z''- isomers. To interconvert these you'd need to break the double bond, and when a bond needs to be broken we call that Configurational Isomerism. Stereocentres are like that too, so enantiomers are configurational isomers. Conformational isomers are different - still stereoisomers, but it's possible to interconvert them without breaking anything, usually by rotation around a single bond. The example below concerns alkanes, which seems silly because we never isolate the alkane isomers under normal conditions - the bond rotation is too easy/fast. But there are some very interesting and important examples of this kind of isomerism, particularly in Nature. | ||
[[Image:3x11 L1 Isomer Summary.png|thumb|center|500px| '''Scheme 1:''' Summary of Isomers]] | [[Image:3x11 L1 Isomer Summary.png|thumb|center|500px| '''Scheme 1:''' Summary of Isomers]] | ||
Revision as of 05:51, 30 March 2012
Chem3x11 Lecture 1
This lecture is an overview of isomerism, then some material on stereocentres and what chiral molecules look like in 1H NMR spectroscopy.
Key concepts
- There are two different kinds of stereoisomers
- Conformations of alkanes governed by sterics and electronics
- Prochiral centres become interesting in a chiral environment
Kinds of Isomerism
Constitutional isomers are the easiest to think about. The molecule is put together differently. If you interviewed each atom in turn, and asked which other atoms they are bonded to, the answers would differ for constitutional isomers. Atoms in stereoisomers would give you the same answer since the atoms are connected to each other the same, only the positions of the atoms in space changes. The easiest kind of stereoisomers to conceptualize are those around a double bond, i.e. E- and Z- isomers. To interconvert these you'd need to break the double bond, and when a bond needs to be broken we call that Configurational Isomerism. Stereocentres are like that too, so enantiomers are configurational isomers. Conformational isomers are different - still stereoisomers, but it's possible to interconvert them without breaking anything, usually by rotation around a single bond. The example below concerns alkanes, which seems silly because we never isolate the alkane isomers under normal conditions - the bond rotation is too easy/fast. But there are some very interesting and important examples of this kind of isomerism, particularly in Nature.
