2. ORGANIC CHEMISTRY HYDROCARBONS

3. Examples of Alkenes ETHENE, C 2 H 4 H C C H OR CH 2 CH 2 PROPENE CH 2 CH CH 3 TASK: Use ball & stick models or sketches to construct and name 3 different structures for C 4 H 8 each one with one double bond. CH 3 CH 2 CH CH 2 CH 3 CH CHCH 3 CH 3 C CH 2 CH 3 BUT-1-ENE BUT-2-ENE 2METHYL PROP 1 ENE H C C H CH 3

4. More Alkenes Illustrate structures of the following alkenes: Pent-1-ene Hex-3-ene 2-methylbut-1-ene Cyclohexene CH 2 CHCH 2 CH 2 CH 3 CH 3 CH 2 CH CHCH 2 CH 3 CH 2 C(CH 3 )CH 2 CH 3 Name the following alkenes CH 3 CH CHCH 2 CH 3 CH 2 CHCH(CH 3 )CH 2 CH 3 Pent-2-ene 3-methylpent-1-ene CH 3 CH(CH 3 )CH CHCH 2 CH 3 2-methylhex-3-ene (CH 3 ) 3 CCH C(CH 3 ) 2 2,4,4-trimethylpent-2-ene

5. Alkynes H-C ≡ C-H H-C ≡ C-CH 3 H-C≡C-CH 2 -CH 3 CH3-C≡C-CH3 Ethyne propyne But–1-yne But–2-yne Very reactive Triple bond unstable! Attracts electrophiles.

6. Naming Aromatics 1.Same rules 2.If benzene is the parent chain “benzene” suffix 3.If benzene is a branch group “phenyl”

7. Structural Isomers Structural isomers are compounds with the same molecular formula but different structural arrangements They will have different physical and chemical properties Example: – pentane – 2-methylbutane – 2,2-dimathylpropane

8. Cis-Trans Isomers Cis-trans isomers occur when different groups of atoms are arranged around a double bond Unlike a single C-C bond that can rotate, the double C=C bond is fixed Same side Opposite side cis-1,2-dichloroethene trans-1,2-dichloroethene

9. GEOMETRIC ISOMERS  There is no rotation about the double bond. Geometric isomerism is a form of STEREOISOMERISM – Same molecular and structural formula but atoms are arranged differently in space GEOMETRIC ISOMERISM each C atom in the double bond has two different atoms/groups attached. BUT–2-ENE CH 3 CH CH CH 3 CH 3 CH 3 C C H H CH 3 H C C H CH 3 cis but-2-ene trans but-2-ene

10. All Hydrocarbons will Undergo Combustion: Complete: CH4 + 2O2 CO2 + 2H2O Incomplete: CH4 + O2 CO2 + CO + C + H2O

11. Alkanes & Aromatics Undergo Substitution Reactions One or more of the hydrogen atoms can be replaced by a halogen You can then add other functional groups by replacing the halogen Requires heat, UV light or a catalyst (not easily done with alkanes! But is easier with aromatics) Alkane + halogen → hydrogen halide + alkyl halide

12. Alkenes & Alkynes Undergo Addition Reactions: · Much greater chemical reactivity than alkanes · Easily undergo addition reactions at room temperature (called addition reaction b/c there is no loss of hydrogen atom(s))

13. Addition Reactions Reactants ProductDescriptive Name \ / | | C = C + HX → - C – C - Hydrohalogenation / \ | | (X = Br, F, I, Cl…) X

14. Markovnikov’s Rule: When a hydrogen halide (e.g. HBr) or water (HOH) is added to an alkene the hydrogen atom will bond to the carbon atom within the multiple bond that already had more hydrogen atoms. CH3-CH2-CH=CH2 + HCl -------------------------> CH3-CH2-CH(Cl)-CH3 This rule doesn't apply for the addition of symmetrical reagents like Br2 or Cl2