FA2008 - CHEM 140A (Lecture Notes - Chapter 5)

FA2008 - CHEM 140A (Lecture Notes - Chapter 5) - Chemistry...

Info iconThis preview shows pages 1–6. Sign up to view the full content.

View Full Document Right Arrow Icon
Chemistry 140A Fall 2008 (K. Albizati) 1 Chapter 5 Stereoisomers So far we have seen several types of isomerism: Cis/trans isomers on rings are examples of diastereomers. Enantiomers are more subtle – they are mirror images (like the relationship between your right and left hand) that cannot be superimposed. This kind of isomerism is important because many biological molecules are single enantiomer stereoisomers. Enantiomerism it is an important structural basis of the chemistry and biology of life. Chirality and Chiral Molecules A molecule that is not superimposable on its mirror image is said to be chiral. The most common way for this non-superimposability (chirality to occur is when a carbon atom in a molecule possesses 4 different groups bonded to it. Consider such a carbon: Isomers same mol formula different structures Stereoisomers Same atom connectivity but different arrangement of atoms in 3D space Diastereomers Stereoisomers that are not mirror images Enantiomers Stereoisomers that are non-superimposable mirror images Constitutional Isomers differ in the order of attachment of the atoms
Background image of page 1

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

View Full DocumentRight Arrow Icon
Chemistry 140A Fall 2008 (K. Albizati) 2 A B C D A B C D A B D C The original molecule and its mirror image cannot be superimposed. They are enantiomers and are said to be enantiomeric. Now try a real molecule: F Br Cl H F Br Cl H F Br H Cl
Background image of page 2
Chemistry 140A Fall 2008 (K. Albizati) 3 Practice picking out Chiral carbon atoms: Chiral? Chiral? Nope. The carbon does not have 4 different groups. A dead giveaway that a carbon is not chiral is if it possesses at least two identical groups, in this case, H. We say that molecules like this are achiral. How about cyclohexane? Nope. All the carbons bear two hydrogens. None of the carbon atoms are chiral. What about…. . One chiral carbon atom – another way to look at this molecule is:
Background image of page 3

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

View Full DocumentRight Arrow Icon
Chemistry 140A Fall 2008 (K. Albizati) 4 Br H CH 3 CH 2 CH 3 Br H H 3 C CH 3 CH 2 What about…. . Monosodium glutamate (MSG) – an example of an α -amino acid, a key class of biological building blocks What about……. Has 2 chiral carbons. Take it to an extreme….
Background image of page 4
Chemistry 140A Fall 2008 (K. Albizati) 5 Where are the chiral carbons? (8 of them) Really, the salient property of chiral molecules is that they are not symmetrical – there is no plane of symmetry anywhere in the molecule. However a compound with more than one chiral carbon may not necessarily exist as a pair of enantiomers. More on this later……… Physical Properties of Enantiomers
Background image of page 5

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

View Full DocumentRight Arrow Icon
Image of page 6
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 18

FA2008 - CHEM 140A (Lecture Notes - Chapter 5) - Chemistry...

This preview shows document pages 1 - 6. Sign up to view the full document.

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