Chemistry 2100 Chapter 12

Alkynes and Alkenes alkene (olefins): C n H 2n alkyne (acetylenes): C n H 2n-2 Ethene Ethyne Ethylene Acetylene

Naming Alkenes and Alkynes Parent name is that of the longest chain that contains the C=C or C ≡ C. Number the chain from the end that gives the lower numbers to the carbons of the C=C or C ≡ C. Locate the C=C or C ≡ C by the number of its first carbon. eneUse -ene to show C=C, -yne for C ≡ C. For cycloalkenes: –Number ring carbons to give carbon 1 and 2 to the C=C bond. –Because of this convention, no need to specify the number of the C=C.

Alkene Isomerism 3-methyl-cis-2-pentene 3-methyl-trans-2-pentene 2-methyl-2-pentene

Conjugation

2

trans-retinal

11-cis-retinal

opsin

rhodopsin opsin

metarhodopsin rhodopsin

metarhodopsin rhodopsin

metarhodopsin rhodopsin

neural impulse metarhodopsin rhodopsin

trans-retinal 11-cis-retinal neural impulse metarhodopsin

trans-retinal 11-cis-retinal neural impulse metarhodopsin

trans-retinal 11-cis-retinal neural impulse metarhodopsin

opsin trans-retinal 11-cis-retinal neural impulse metarhodopsin

opsin trans-retinal 11-cis-retinal neural impulse metarhodopsin

Terpenes – natural polyenes limonene (orange, dill) myrcene (bay) geraniol (rose) menthol (mint) carvone (spearmint, dill) zingiberene (ginger)  -selinene (celery) caryophyllene (cloves)

squalene

cholesterol ~25 steps lanosterol

Making Alkenes tetra tri di mono

Reactions of Alkenes Hydrogenation (cis or trans)

Partially Hydrogenated Vegetable Oil "partially hydrogenated vegetable oil"

Halogenation CH 2 Cl 2 RT ∆ / h CH 2 Cl 2 Cl 2

Acid Addition CH 2 Cl 2 minor major H 2 SO 4

Addition of HX Addition of HX (HCl, HBr, or HI) to an alkene gives a haloalkane. –H adds to one carbon of the C=C and X to the other. regioselective. –Reaction is regioselective. One direction of bond forming (or bond breaking) occurs in preference to all other directions. –Markovnikov’s rule: –Markovnikov’s rule: H adds to the less substituted carbon and X to the more substituted carbon. 37

Common Mechanism Steps Pattern 1: Add a proton An acid is a proton donor and a base is a proton acceptor. We can use curved arrows to show how a proton transfer occurs. Patterns 2: Take a proton away. If we run the above reaction, in reverse it corresponds to taking a proton away. 38

Common Mechanism Steps Pattern 3: Reaction of an electrophile and a nucleophile to form a new covalent bond. An electrophile is an electron-poor species that can accept a pair of electrons to form a new covalent bond. A nucleophile is an electron-rich species that can donate a pair of electrons to form a new covalent bond. 39

Common Mechanism Steps Pattern 4: Reaction of a proton donor with a carbon-carbon double bond to form a new covalent bond. The double bond provides both of the electrons that forms the new covalent bond. In the following reaction we show the hydronium ion as the proton donor. While the above equation is the most accurate way to show the proton transfer, we will simplify the equation to just show the proton and formation of the new covalent bond. 40

Addition of HCl to 2-Butene Step 1: Add a proton –Reaction of the carbon-carbon double bond with H + gives a secondary (2°) carbocation intermediate, a species containing a carbon atom with only three bonds to it and bearing a positive charge. Step 2: Reaction of an electrophile and a nucleophile to form a new carbon-carbon bond. –Reaction of the carbocation intermediate with chloride ion completes the addition. 41

Polymerization Z = CH 3 polypropylene Z = Cl PVC Z = CN polyacrylonitrile Z = OH polyvinyl alcohol polypropylene PVC polyacrylonitrile polyvinyl alcohol

Polymerization –Show the structure of a polymer by placing parentheses around the repeating monomer unit. –Place a subscript, n, outside the parentheses to indicate that this unit repeats n times. –The structure of a polymer chain can be reproduced by repeating the enclosed structure in both directions. –The following is a section of polypropene (polypropylene). 43

Polymers & Health Pthalate, plasticizer Bisphenol A = hard shell plastic