1 ALKENES ALKENES are hydrocarbons: * with C=C bonds; * of general formula C n H 2n ; * having 120° bond angles and trigonal planar shape around the C= ;

2 Examples: ethylene H H C=C H H H CH 3 C=C H propene

3 A C=C is made up of 2 types of bonds: The  bond is a standard C-C. The  bond is weaker than . Overall, the C=C is stronger (but not 2x stronger) and shorter than a C-C.

4 Naming alkenes 1. Find longest chain of C that contains the C=C. 2. Number chain to give one of the C in C=C the lowest possible locant. 3. Change name of parent alkane to alkene.

5 4. Give the lower locant number for a C=C in front of the parent alkene name. 5. Number and name other substituents as usual.

6 Example CH 3 -CH-CH 2 -CH-CH=CH-CH 3 Br CH 2 CH 3 7 carbons in chain= hept ending = ene # from right = 2-heptene

7 CH 3 -CH-CH 2 -CH-CH=CH-CH 3 Br CH 2 CH bromo ethyl complete name =6-bromo-4-ethyl-2-heptene

8 Naming cycloalkenes 1. Start numbering of ring C at one of the C in C=C. 2. Position #2 is the second C of the C=C. 3. Count in the direction which gives other substituents the lower set of locant #.

9 Example CH 2 CH 3 Br complete name=4-bromo-3-ethylcyclohexene

10 Stereoisomers are: isomers * isomers (= same formula), having same constitution * having same constitution (= same kinds & sequence of bonds), but permanently different arrangements of groups in space. * but permanently different arrangements of groups in space.

11 Stereoisomers are of several types, depending on what phenomenon causes them to exist. Geometric isomers Geometric isomers are stereoisomers because of restricted rotation around bonds (C-C or C=C).

12 In alkenes the two bonds between the C of the C=C prevents free rotation of the groups around the C=C bond. cistrans cis and trans geometric isomers have different physical and chemical properties: they are distinctly different compounds.

13 Compare the corresponding alkenes: H H CH 3 H C=C CH 3 CH 3 H CH 3 cis-2-butenetrans-2-butene cis-2-butene trans-2-butene

14 When can an alkene exist as geometric isomers? ==> the same C of C=C must have two different groups bonded to it. CH 3 CH 2 H C=C 1-butene: no C=C 1-butene: no H H cis or trans H H cis or trans

15 CH 3 C=C H CH 2 CH 3 2-methyl-2-pentene has no geometric isomer

16 Addition Reactions are typical of alkenes. General schematic equation: C=C + X-Y ----> C=C + X-Y ----> C-C X Y X Y

17 In an addition reaction: * the  bond of C=C “breaks” * the covalent bond between X,Y “breaks” * new C-X and C-Y  bonds form

18 When bonds break and form in reactions, the shared electron pairs are scrambled or rearranged... to be shared by different atoms.

19 In the addition reaction, X and Y can be the same element or different elements. Examples of X=Y H 2, Cl 2, Br 2 Example of X, Y Different H 2 O written as H-OH

20 CH 3 -CH=CH 2 H 2 H 2, Pt (metal catalyst) CH 3 CH-CH 2 = CH 3 CH 2 CH 3 H H

21 so, the general equation is: alkene + H 2 --> alkane This process is called catalytic reduction or hydrogenation because the H 2 is added with the help of a catalyst.

22 HOH (water) alone does not react with an alkene – it requires a catalyst. Addition of water to the alkene C=C is called hydration. In lab the catalyst is H + (acid), often from H 2 SO 4. In a living cell the catalyst is an enzyme.

23 When alkene is symmetrical, one addition product forms: H + HOH ---> CH 3 -CH=CH-CH 3 + H-OH ---> CH 3 -CH-CH-CH 3 CH 3 -CH-CH-CH 3 H OH OH H H OH OH H either way, same product either way, same product

24 If alkene is unsymmetrical: HOH + H + CH 3 -CH=CH 2 + H-OH + H + ---> ONLY! CH 3 -CH-CH 2 ONLY! OHH OH H NONE of this forms: CH 3 -CH-CH 2 HOH H OH

25 Markovnikov found: HX H “when H-X adds to a C=C of alkene, H attaches to the C of C=C that already had more H bonded to it.” HX H-X = HClHBrHIHOH H-Cl, H-Br, H-I, H-OH

26 Example: CH 3 CH 2 CH=CH 2 + H 2 O ----> CH 3 CH 2 CH-CH 2 OH H more commonly written as CH 3 CH 2 CH-CH 3 OH H+H+

27 Alkynes are hydrocarbons that: * contain a C  C * have general formula C n H 2n-2 * have linear geometry, 180° bond angle

28 Examples of Alkynes Acetylene H-C C-H Acetylene CH 3 CH 2 -C C-H 1-butyne, a terminal alkyne CH 3 -C C-CH 3 2-butyne, an internal alkyne

29 Naming Alkynes: 1. find longest chain that includes C C. 2. change parent name of longest chain from “alkane” to “alkyne.” 3. give lowest possible locant # to the first C of C C. 4. locate other substituents as usual.

30 Naming example Cl CH 3 CH-CH-CH 2 -C C-CH 3 CH 36-chloro-5-methyl-2-heptyne

31 Aromatic Compounds: * usually contain six double-bonded carbon atoms in a ring; * have alternating C-C & C=C; * have a flat ring structure; * do NOT undergo addition reactions like alkenes.

32 Ways to draw aromatic ring: or Each vertex = C; each C in ring can have one more bond. If no connection shown, bond is to H.

33 Some important aromatic compounds: CH 3 NH 2 OH benzene aniline toluene phenol

34 When a benzene ring is a substituent on a parent chain, it is called “phenyl” : CH 3 CH=CCH 2 CH 2 CH 2 CH 2 CH 3 3-phenyl-2-octene