Chem 105X Friday, Dec. 2, Chapter 10, Kotz Organic Chemistry

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1 our Exam 4 (Chap 9, 10, 11) will be given in this room Friday, Dec. 9. A practice exam is posted on the course website. Review for the exam will occur Wednesday, Dec. 7 in class. Chem 105X Friday, Dec. 2, 2011 Chapter 10, Kotz Organic Chemistry Review alkane structures and naming Optical Isomers Alkenes Saturated and unsaturated fats Alkynes Aromatic hydrocarbons and petroleum products 12/2/2011 1

2 Which ones are isomers? A and B 2. A and C 3. B and C A and B A and C B and C A, B, and C none 4. A, B, and C 5. none

3 Isomers have the same molecular formula, but different bonding patterns. 2. A and C Fill in the implicit s, and count em. C 7 16 C 7 14 C 7 16 N.B. including a ringdecreases the number of s by 2. 12/2/2011 3

4 The systematic (I.U.P.A.C.) name for the following compound is.. 29% 24% 47% 1. 1,2,6-trimethylhexane 2. 2-ethylheptane 1,2,6-trimethy... 2-ethylheptane 3-methyloctane 3. 3-methyloctane

5 free download yes NO NO Find the longest chainas the parent chain for the molecule.

6 Optical Isomers Molecules containing a tetrahedral atomwithfour different atoms or groupscan exist in right-handed and left-handed forms. W X C Y These have identical physical properties, excepthow they interact with polarized light. One isomer twists polarized light beam clockwise, the other isomer twists it counterclockwise. Z ence, they are optical isomers. This type of molecule is chiral (ky rəl). 3 C F 3 C CClF Cl 12/2/2011 6

7 Fclethane-both.hin 12/2/2011 7

8 Optical Isomers amino acids O 2 C N 2 2 N CO 2 L-phenylalanine (l) tastes bitter. D-phenylalanine (r) tastes sweet. The L isomers of amino acids occur naturally in proteins. D isomers are rare. 12/2/2011 8

9 Alkenes contain C=C functional group This complicates the structural isomer situation somewhat: C 6 12 isomers on the board. In class, we counted 10: 1-, 2-, and 3-hexene 2-methyl-1-pentene; 2-methyl-2-pentene; 4-methyl-1-pentene; 4-methyl-2-pentene 3-methyl-1-pentene; 3-methyl-2-pentene; 2-ethyl-1-butene There are 3 more, for a total of 13: 3,3-dimethyl-1-butene; 2,3-dimethyl-2-butene; 2,3-dimethyl-1-butene 12/2/2011 9

10 Alkene systematic names (1) Find longest chainin molecule containing both C s of C=C (2) Number the chain starting at end closer to C=C. (3) Write the name of the parent chain including a location for the 1 st C of the C=C. C 3 C 3 3 C C C C C C ,5-dimethyl- 2-hexene 6 (4) Identify the number(di, tri, tetra etc) and type(methyl, ethyl, etc) of substituents. (5) Make prefix with locations ( 2,2 ) of the substituents, number ( di ), and type ( methyl ). 12/2/

11 Alkenes contain C=C bond (C n 2n ) Some alkenes can exist in cis- or trans- geometric isomers 3 C C 3 trans- Same atoms or groups compare their positions on C=C. cis- 3 C C 3 12/2/

12 Geometric isomers (cis and trans on C=C) No C=C bonds contain π-bond that depends on parallel orientation of the 2 p-orbitals on bonded carbons. This prevents twisting around the bond. Therefore C=C bonds containing different atoms can exist as cis-or trans-isomers C 3 C l C l C l C l C l C l C l C l C 3 cis isomers trans isomers 12/2/

13 trans-4,5-diethyl-4-nonene 3 C C C C 3 12/2/

14 Alkanes are referred to as saturatedhydrocarbons. They have the maximum number of sfor a given # of C s. Alkenes are unsaturated - they have fewer s. Unsaturated fatscontain C=C bonds along the fatty acid chain. These are usually cis- because the C=C plays a structural role in lipid bilayers. 12/2/

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16 glycerol phosphate Saturated fatty acyl group In animals, the straightchainsof saturated fatty acidspack tightly into a lipid bilayer. Section of lipid bilayer These function properlyat a cell temperature of 37 C. 12/2/

17 In plantand bacterialcells, membranes contain fatty acid components rich in cis-double bonds. These chains are kinked by the cisbond, resulting in disordered lipid bilayer that is more fluid.it remains flexible at low temperatures, which maintains the proper biological functions the cell membrane. 12/2/

18 trans-double bonds in commercial fats arecreatedduring partial hydrogenation reactionsthat add 2 to some C=C bonds using a metal catalyst. Some cis-double bonds go to transduring this process. The trans-acid packs into membranes in a manner similar to saturated fats. This may be the basis of the unhealthy effects of fats containing lots of trans fatty acids. 12/2/

19 Alkynes C C 12/2/

20 Alkynescontain a C C triple bond. Each sp-hybridized carbon contains two unhybridized p-orbitals The four p-orbitals combine to form two π-bonds. C C 12/2/

21 -C C- common name is acetylene ( ethyne is the systematic name, but is not used.) C C 2 C C 3 C 2 C C C 2 C methyl-3-octyne Uses: acetylene is welding gas larger alkynes used as synthesis intermediates because the C C bond can be modified in many ways. Some natural molecules such as dynemicin anti-cancer drug contain C C bonds. 12/2/

22 Aromatic hydrocarbons 12/2/

23 Aromatic hydrocarbons contain one or more benzene rings. C C C C C C C C C C C C Benzene itself is C 6 6. Itis aresonance hybrid of two equivalent forms. This leads to an unusually stablemolecule. This is called an aromatic ring which refers to the special stability of 6 π-electrons in a ring of sp 2 -atoms. Sometimes written this way to emphasize bonding symmetry: or 12/2/

24 Enhanced stabilityof the aromatic ring is due to formation of a low-energy π-molecular orbital extending around the ring. 12/2/

25 C 3 C 3 C 3 C 3 C 3 C 3 C 3 Toluene (methylbenzene) ortho-xylene meta-xylene para-xylene 12/2/

26 Binding energy (kcal/mol)* Toluene (methylbenzene) is 28 kcal/mol more stable than the next-most stable C 7 8 isomer C 2 C 3 Toluene C 3 3 C C 2 2 C * calculated with PM3 semi-empirical method C 2 Not aromatic Aromatic There are >100 isomers of C 7 8! 12/2/

27 ow many isomers of trimethylbenzene exist?

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29 The End 12/2/