Department of Chemistry CHEM1020 General Chemistry *********************************************** Instructor: Dr. Hong Zhang Foster Hall, Room 221 Tel:

CHEM1020/General Chemistry _________________________________________ Chapter 9. (L3)-Organic Chemistry Today’s Outline..Alkenes..Alkynes..Unsaturated hydrocarbons..Aromatic hydrocarbons

Chapter 9. (L3)-Organic Chemistry Alkenes …Alkenes are those that have one or more double C-to-C bonding hydrocarbons Example: CH 2 =CH 2, ethylene, C 2 H 4 CH 3 -CH=CH 2, propene, C 3 H 6

Chapter 9. (L3)-Organic Chemistry Alkenes …Alkenes are double C-to-C bonding hydrocarbons General molecular formula: C n H 2n Isomers, example: CH 3 -CH 2 -CH=CH 2, 1-butene, C 4 H 8 CH 3 -CH=CH-CH 3, 2-butene, C 4 H 8

Chapter 9. (L3)-Organic Chemistry Alkenes …Ethylene is the most important organic chemical. …Annual US production: > 20 billion kg …> half is used to produce polyethylene, the most familiar plastics

Chapter 9. (L3)-Organic Chemistry Alkynes …Alkynes are those that have one or more triple C-to-C bonding hydrocarbons Example: CH=CH, acetylene, or ethyne, C 2 H 2 H-C=C-H General molecular formula: C n H 2n-2

Chapter 9. (L3)-Organic Chemistry Alkynes …Alkynes are used in oxyacetylene torches for cutting and welding metals. …Acetylene is also converted to a variety of other chemical products.

Chapter 9. (L3)-Organic Chemistry Alkynes …Unsaturated hydrocarbons Alkenes and alkynes are collectively called unsaturated hydrocarbons because hydrogen can be added into these organic molecules Unsaturation means the carbon does not have the maximum number of hydrogen it can have or means the hydrocarbons have double or triple bonds.

Chapter 9. (L3)-Organic Chemistry Alkynes …Unsaturated hydrocarbons Alkenes and alkynes are collectively called unsaturated hydrocarbons because hydrogen can be added into these organic molecules: CH 2 =CH 2 + H 2 = CH 3 -CH 3 CH=CH + 2H 2 = CH 3 -CH 3

Chapter 9. (L3)-Organic Chemistry Alkynes …Properties of alkenes and alkynes The physical properties of alkenes and alkynes are quite similar to those of the corresponding alkanes. Those with 2-4 C are gases Those with 5-18 C are liquids Those with >18 C are solids Alkenes and alkanes are insoluble in water, hydrophobic. They like to form polymers.

Chapter 9. (L3)-Organic Chemistry Aromatic hydrocarbons …A special type of cyclic or closed ring hydrocarbon, represented by benzene Discovered by Michael Faraday in Molecular formula: C 6 H 6 By looking at its molecular formula, one knows that it is unsaturated, probably with double bonds.

Chapter 9. (L3)-Organic Chemistry Aromatic hydrocarbons …The structure of benzene had troubled chemists for a long time until 1865 In 1865, August Kekule proposed the famous ring structure as shown on the board It has 6 C and 6 H, with three alternated occurrence of double C-to-C bonds More research indicated that the “double-bond nature” is evenly shared by all the 6 carbons. Modern structure of benzene is as shown on the board, a hybrid structure: It has 6 neither single nor double, but in between single and double bonds.

Chapter 9. (L3)-Organic Chemistry Aromatic hydrocarbons …The special structure of benzene makes it very stable. …Benzenes and similar compounds and those containing benzene rings are called aromatic compounds because they generally have the aromatic smell. Some examples of aromatic compounds, shown on boards (pp. 248)

Chapter 9. (L3)-Organic Chemistry Aromatic hydrocarbons …Properties of aromatic compounds usually liquids floating on water as solvents and fuels used to make other benzene derivatives it can cause leukemia after long exposure toxic, avoid too much exposure

Chapter 9. (L3)-Organic Chemistry Quiz Time Alkenes are a type of hydrocarbons that have (a) C-to-C double bond; (b) C-to-C triple bond; (c) C-to-C single bond; (d) no C-to-C bonding.

Chapter 9. (L3)-Organic Chemistry Quiz Time Alkynes are a type of hydrocarbons that have (a) C-to-C double bond; (b) C-to-C triple bond; (c) C-to-C single bond; (d) no C-to-C bonding.

Chapter 9. (L3)-Organic Chemistry Quiz Time The general molecular formula for Alkenes is (a) C n H n ; (b) C n H 2n ; (c) C n H 2n+2 ; (d) C n H n+2.

Chapter 9. (L3)-Organic Chemistry Quiz Time The general molecular formula for Alkynes is (a) C n H n ; (b) C n H 2n ; (c) C n H 2n-2 ; (d) C n H n+2.

Chapter 9. (L3)-Organic Chemistry Quiz Time The molecular formula for benzene is (a) C 6 H 4 ; (b) C 6 H 8 ; (c) C 6 H 12 ; (d) C 6 H 6.

Chapter 9. (L3)-Organic Chemistry Quiz Time The aromatic compounds are organic molecules that have (a) oxygen atoms; (b) single C-to-C bonds; (c) benzene rings or benzene related structures; (d) triple bonds.