Organic Chem Chapter 5 Part 1 PDF

Organic Chem Chapter 5 Part 1 See end of Part 1 for start of Homework for chapter 5 1 This chapter deals with the orientation of molecules and how their 3-D structure allows reactions to occur. Specific products can be made which may...

Organic Chem Chapter 5 Part 1 See end of Part 1 for start of Homework for chapter 5 1 This chapter deals with the orientation of molecules and how their 3-D structure allows reactions to occur. Specific products can be made which may look the similar but are different in the position of an atom or functional group when comparing the bonding orientation about a specific atom This chapter does not have reactions but several repetitive slides to emphasize the discussion It is broken into 2 parts to allow the start of HW (part 1) so that those concepts can be used further in the chapter (part 2) 2  Stereochemistry Deals with the 3-D structure of a molecule. minor differences between molecules can result in vastly different properties. Higher MP; not as sweet 3  Stereochemistry of Starch and Cellulose example from textbook In cellulose, the O atom joins two rings using equatorial bonds. In starch, the O atom joins two rings using one equatorial and one axial bond. Due to these differences in stereochemistry, humans can metabolize starch for energy but we cannot digest cellulose. 4  3-D Structure of Starch and Cellulose Figure 5.2 5  Isomers are different compounds with the same molecular formula. Two major classes constitutional isomers and stereoisomers. Constitutional/structural Stereoisomers: isomers Differ only in the way the Different IUPAC names atoms are oriented in space. Same or different functional groups Have identical IUPAC names (except for a prefix like cis or Different physical trans). properties Different chemical Always have the same properties functional group(s). Differ in configuration (three- dimensional arrangement). May have some property differences 6  Constitutional and Stereoisomers Figure 5.3 7  Superimposable (Achiral) Objects Sequence in textbook is different..nonsuperimposable is first Other molecules are like socks. Two socks from a pair are mirror images that are superimposable. A sock and its mirror image are identical. A molecule or object that is superimposable on its mirror image is said to be achiral. To superimpose means to align all parts of two objects 8  Achiral Molecules ©2020 McGraw-Hill Education. 9  Nonsuperimposable Mirror Images mirror images may or may not be superimposable. To superimpose means to align all parts of two objects A molecule (or object) that is not superimposable on its mirror image is said to be chiral. Chiral: asymmetric in such a way that the structure and its mirror image are not superimposable 10 Example of nonsuperimposable mirror image Left and right hands are mirror images, but they are not identical, or superimposable. 11 mirror images Move one on top of the other; only black bonds super impose 12  These groups can be anything as long as they are different https://www.researchgate.net/figure/Non-superimposable-mirror-images-of-optical-isomers_fig1_224000258 13  Chiral Molecules The molecule labeled A and its mirror image labeled B are not superimposable. CHBrClF is a chiral molecule, and A and B are different compounds. These are stereoisomers— enantiomers (nonsuperimposable mirror images) A carbon atom with four different groups is a tetrahedral stereogenic center, 14  Stereogenic Centers meaning: any point in a molecule, though not necessarily an atom, bearing different substituents, such that interchanging any two substituents leads to a stereoisomer. In general, a molecule with no stereogenic centers will not be chiral (exceptions to this will be considered in section 17.5). With one stereogenic center, a molecule will always be chiral. With two or more stereogenic centers, a molecule may or may not be chiral. 15  Planes of Symmetry A plane of symmetry is a mirror plane that cuts the molecule in half, so that one half of the molecule is a reflection of the other half. Achiral molecules usually contain a plane of symmetry (in any conformation) but chiral molecules do not. 16  Summary of Chirality Everything has a mirror image. The fundamental question is whether a molecule and its mirror image are superimposable. If not, they are chiral and do not contain a plane of symmetry. If they are superimposable, they are achiral and will contain a plane of symmetry. The terms stereogenic center and chiral molecule are related but distinct. A chiral molecule must have one or more stereogenic centers. 17  Stereogenic Centers To locate a stereogenic center, examine each tetrahedral carbon atom in a molecule, and look at the four groups—not the four atoms—bonded to it. Always omit from consideration all C atoms that cannot be tetrahedral stereogenic centers. These include: CH2 and CH3 groups Any sp or sp2 hybridized C 18  Multiple Stereogenic Centers Larger organic molecules can have many stereogenic centers. Each center has 4 different Note: Look for what is being asked, not groups bonded to the carbon how large or complicated the molecule appears to be….. 19  Is this molecule chiral? (see problem 5.5 pg 185 as an example) But rotation produces a conformation with a plane of symmetry..achiral 2 centers that are nonsuperimposable mirror images 20  Enantiomers Enantiomers are non-superimposable mirror image molecules. Any molecule with one stereogenic center exists as a pair of enantiomers. 21  Example of the importance of understanding enantiomers One enantiomer of a drug may effectively treat a disease whereas its mirror image may be ineffective or toxic. Changing the orientation of the substituents on naproxen converts it from a common anti-inflammatory agent into a harmful liver toxin. 22  Drawing Enantiomers To draw both enantiomers of a chiral compound such as 2-butanol, use the typical convention for depicting a tetrahedron. To form the first enantiomer, arbitrarily place the four groups—H, OH, CH3 and CH2CH3—on any bond to the stereogenic center. Then draw the mirror image. 23 Chapt 5 part 1 ends here Start of Chapter 5 HW: Inside the chapter: 5.2 (pg 182), 5.3, 5.6a, b, c; 5.9 a, b Look at sample problem 5.2 (pg 188); peruse problem 5.8 and its difficulties as molecules get larger End of chapter: 5.41 a, b; 5.42 a, b; 5.43 24