Alkenes Alkynes and aromatic compounds Hydrocarbons contain only

Alkenes, Alkynes and aromatic compounds Hydrocarbons (contain only carbon and hydrogen) a) Saturated: (Contain only single bonds) Alkanes (Cn. H 2 N + 2 ) Cycloalkanes (Cn. H 2 N ) b) Unsaturated: contain Alkenes: double bonds (, , , Cn. H 2 N) Alkynes: triple bonds ((Cn. H 2 N - 2) Aromatic: benzene like compounds 1

Facts about double and triple bonds 2

Biologically active alkene derivatives 3

Linoleic acid α-Linolenic acid Arachidonic acid 4

Isoprene = 2 -Methyl-1, 3 -butadiene

Nomenclature of alkenes and Alkynes 1) 2) 3) 4) The ending ene is used for alkenes and yne for alkynes Select the longest chain that includes both carbons of the multiple bond Number the chain from the end nearest to the multiple bond Indicate the position of the multiple. Examples 6

Isomers and common names of simple alkenes 7

Nomenclature of compounds containing more than one multiple bond 1) Number from the end nearest to the multiple bond. If a double and a triple bond are equidistant from he end, the double bond receives the lowest numbers Example 8

Compounds containing more than one double bond Classification according to the position of double bonds 9

Cis-Trans (Z-E) Isomerism in Alkenes Because rotation at carbon–carbon double bonds is restricted, cis–trans isomerism (geometric isomerism) is possible. If the two groups are identical we distinguish the two isomers by adding the prefix cis (same side) or trans (opposite sides) Example 10

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If the groups attached to the double bond are different, we distinguish the two isomers by adding the prefix Z (same side) or E (opposite sides) depending on the atomic number of the atoms attached to each end of the double bond 12

Reactions of Alkenes ØThe most common reaction of alkenes is addition of a reagent to the carbons of the double bond to give a product with a C-C single bond. ØWhat is the difference between addition and substitution reactions? Substitution: Addition: 13

Example for reaction a: 14

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Example 1 for reaction b: 16

Example 2 for reaction b: When an unsymmetric reagent adds to an unsymmetric alkene, the electropositive part of the reagent bonds to the carbon of the double bond that has the greater number of hydrogen atoms attached to it 17

Example for reaction c: 18

c. Example for reaction C: 19

d. A polymer is a large molecule, usually with a high molecular weight, built up from small repeating units. The simple molecule from which these repeating units are derived is called a monomer, and the process of converting a monomer to a polymer is called polymerization. 20

Reactions of Alkynes 21

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Examples to reactions a: 23

Aromatic Compounds 24

Ø Benzene, C 6 H 6, is the parent hydrocarbon of the especially stable compounds known as aromatic compounds. 25

Preservative for urine specimens Nomenclature of Aromatic Compounds 26

Nomenclature of Aromatic Compounds Ø When two 27 substituents are present, three isomeric structures are possible. They are designated by the prefixes ortho- , meta-, and para, which are usually abbreviated as o- , m-, and p, respectively.

Examples: 28

Examples: 29

Reactions of aromatic compounds The most common reactions of aromatic compounds involve substitution of other atoms or groups for a ring hydrogen on the aromatic unit. Here are some typical substitution reactions of benzene. 30

Polycyclic Aromatic Hydrocarbons Ø Naphthalene is a planar molecule with two fused benzene rings. The two rings share two carbon atoms. Ø Phenanthrene is an isomer of anthracene and is considered to be the basic structure of many important compounds like cholesterol, male and female sex hormones, and Vitamin D. 31

Ø Some polycyclic aromatic compounds such as benzo[a]pyrene are cancerogenic Ø Cancerogenic compounds can produce a tumor on mice in a short time when only trace amounts are painted on the skin. Ø These carcinogenic hydrocarbons are present not only in coal tar but also in tobacco smoke and can be formed in barbecuing meat 32