ALKANES THE HYDROCARBONS
ALKANES: • a. Simplest hydrocarbons b. Saturated hydrocarbons c. Aliphatic hydrocarbon: d. How they are classified: Hydrocarbons a. Alkanes—single bonds; saturated b. Alkenes—double bonds; unsaturated c. Alkynes—triple bonds; unsaturated d. Aromatics—ring structure; unsaturated
HYDROCARBONS OPEN CLOSED (RING) Saturated Unsaturated Benzene related Non-Benzene Related Double bonds Triple bonds Alkanes Cycloalkanes Cycloalkenes cycloalkynes Aromatics Alkenes Alkynes
2. General formula: CnH2n + 2 3. Functional group- differentiates molecules of organic compounds of one class from those in another. 4. Know the first 10 prefixes of the alkane family meth – 1 carbon hex – 6 carbons eth – 2 carbons hept – 7 carbons prop – 3 carbons oct – 8 carbons but – 4 carbons non – 9 carbons pent – 5 carbons dec – 10 carbons
Prefixes 11-20 • 11 undecane • 12 dodecane • 13 tridecane • 14 tetradecane • 15 pentadecane • 16 hexadecane • 17 heptadecane • 18 octadecane • 19 nonadecane • 20 icosane
5. General terms: a. Molecular structure: b. Structural formula: c. Condensed formula: d. Alkyl group—partial structure formed by removing a hydrogen from an alkane. Ex. CH3 e. Alkyl halide—a carbon bonded to a halogen 6. Four possible degrees of alkyl substitution for carbon atoms: a. Primary carbon (10)—bonded to one other carbon. b. Secondary carbon (20)—bonded to two other carbons. c. Tertiary carbon (30)—bonded to three carbons d. Quaternary carbon (40)—bonded to four carbons
7. IUPAC system of nomenclature: International Union of Pure and Applied Chemistry 8. Naming alkanes: ( rules ) 1. Find the longest continuous chain of carbon atoms and assign a name to the parent. a. If the alkane is in a continuous chain and there is no branching, they are called “normal” alkanes. (n-alkane) 2. Number the longest chain. The carbon atoms in the longest chain are numbered consecutively from the end that will give the lower number to any carbon to which a “group” is attached. a. Remember that the groups could be methyl, ethyl, propyl, etc.
3. If there are two or more identical groups, we use prefixes. Ex. di=2, tri=3, tetra=4, penta=5, hexa=6, hepta=7, etc. **Show examples 4. If there are two or more different groups, we put all of them into the prefix in alphabetical order. Examples: 5. Name the halogens using these prefixes: F = fluoro Br = bromo Cl = chloro I = iodo 9. Important Branched Alkyl Groups:
10. Cycloalkanes (rules for naming): 1. We may begin at any position and may proceed either clockwise or counterclockwise, but we must end up with the lowest possible numbers 2. Three common cycloalkanes: cyclopropane cyclohexane cyclopentane
11. Isomers—has the same numbers and kinds of atoms but differ in the way the atoms are arranged. a. Structural isomers– has the same molecular formulas, but they have different atom-to-atom bonding sequences. Ex. Butane Isobutane Molecular formulas and possible structural isomers of alkanes.
MOLECULAR FORMULA # OF POSSIBLE ISOMERS C4H10 2 C5H12 3 C6H14 5 C7H16 9 C8H18 18 C9H20 35 C10H22 75 C15H32 4,347 C20H42 366,319 C30H62 4,111,846,763
11. Major uses of alkanes: a. C1—C4 1. gases at room temp. 2. methane & ethane handled as compressed gases 3. Liquefied natural gas, methane, is transported in special refrigerated tankers. 4. Propane & butane are easily liquefied at room temp—stored in low-pressure cylinders of liquefied petroleum gas (LPG) tankers for transportation. 1. more cost efficient for tractor fuels than gasoline and diesel fuel. 2. replace Freon's as propellants in aerosol cans.
b. C5—C8 1. very volatile liquids 2. their isomers are the 10 constituents of gasoline c. C9—C16 1. higher boiling liquids 2. used in kerosene, jet fuel, and diesel fuel d. C16 and higher: 12. Properties of Alkanes: a. Hydrophobic b. Why would the alkanes being hydrophobic be important? c. B/c this makes them good lubricants and preservatives for metal thus keeping water from reaching the metal surface and causing corrosion.
d. Old term for alkanes is “paraffin” which means “little activity”. e. Show little chemical affinity for other substances and inert to most lab reagents. f. They do react with O2 and Cl2 in combustion rxns. Ex. CH4 + 2O2 -----------> CO2 + 2HOH g. Less dense than HOH, so they tend to float on top of HOH. 13. Hydrocarbons in Earth: a. Major components of natural gas, petroleum, and coal. b. Natural gas—gaseous hydrocarbons; petroleum—liquid h/c’s c. Petroleum—also called “crude oil”, found in large lakes deep underground d. Natural gas—found in the space above petroleum
14. Fossil fuels: a. Petroleum: 1. referred to as “black gold” 2. formed from the gradual decay of ocean-dwelling microscopic animals. 3. most is burned as fuel such as cars, trains, trucks, airplanes, etc. 4. more than half of all industrial synthetic organic compounds are made from petroleum products. Ex. dyes, drugs, plastics, artificial fibers, detergents, insecticides, etc. b. Coal & its forms: 1. Anthracite—hard coal; 90% pure carbon; purest coal found in nature. 2. Coke—purer than anthracite, but synthetic.
3. bituminous—soft coal; 70-80% carbon; contains sulfur, giving off the “stinky” odor. 4. lignite—least decayed form of coal; 30-50% carbon; burns with a smoky flame. 5. peat—simplest form; partially decomposed organic matter. 15. Petroleum Refining: The steps!! a. Fractionaldistillation—its products are not pure alkanes, but mixtures of alkanes alkenes, alkynes, and cyclic hydrocarbons. b. Catalyticcracking—converts the less valuable fractions to more valuable products. 1. hydro cracking—done in presence of hydrogen, and the product is a mixture of alkanes, free sulfur and nitrogen impurities.
Naphtha normally refers to a number of different flammable liquid mixtures of hydrocarbons, i.e. a distillation product from petroleum or coal tar boiling in a certain range and containing certain hydrocarbons, a broad term encompassing any volatile, flammable liquid hydrocarbon mixture. Naphtha is used primarily as feedstock. For producing a high octanegasoline component (via the catalytic reforming process), it is also used in the petrochemical industry for producing olefins in steam crackers and in the chemical industry for solvent (cleaning) applications.
16. Chemical reactions of alkanes: a. Do not easily react b/c the C-H bond is very stable and broken only under unusual or violent conditions. b. Alkanes go through oxidation (combustion) 2CH4 + 3O2 --------> 2CO + 4HOH 1. oxidation is the process where we extract the energy of chemical bonds stored in the fossil fuels. 2. oxidation is one of the most vital of all chemical rxns. c. In many cases CO, rather than CO2, is produced. d. Why would CO being produced be more dangerous to us? Because the hemoglobin in the blood has a greater affinity for CO than it does for oxygen, it is less able to pick up and distribute O2. In extreme cases CO can cause death quickly, or nausea, headaches, and impaired sensory responses.
e. Most common source of CO is automobile. f. By 1990, CO emissions accounted for 48% of all air pollutants in the U.S. g. Substitution—only under certain conditions 1. Ex. when liquid bromine is added to a test tube containing ethane gas in bright sunlight, the following reaction occurs: UV light 2. C2H6 + Br2 ------> C2H5Br + HBr h. To get them to react quickly, two methods are generally used: 1. change the physical conditions of the reaction. Ex. increase the temp. and/or pressure. 2. or make use of electricity, x-rays, UV light, or some form of electromagnetic radiation.
i. Sometimes a catalyst is used. 17. Halogenated hydrocarbons: a. Can react with the halogens to form alkyl halides. b. R = alkyl group; X = halogen General formula: RX c. Methane + chlorine -------> CH4 + Cl2 ------> CH3Cl + CH2Cl2 + CHCl3 + CCl4 + HCl methyl methylene chloroform carbon hydrochloric chloride chloride tetrachloride acid d. Heat or light is usually needed to initiate this halogenation. e. Bromine containing halogenated hydrocarbons are called “halons”. Ex. CBrClF2 CBrF3 Bromochlorodifluoromethane bromotrifluoromethane (Halon-1211) (halon-1301)
f. Alkyl halides are very reactive compounds. g. Chlorofluorocarbons (CFC’s)—danger to the ozone layer. 1. Freon—a commercial CFC; (CF2Cl2) 18. Chlorofluorocarbons and the environment: a. First used in the 1930’s as refrigerants. b. Also used as: propellants in spray cans, cleaning material in the electronics and dry-cleaning industries, and in the manufacture of plastic foams. c. Before 1970, CFC’s were thought to be relatively inert in the lower atmosphere, very stable, colorless, nonflammable, and nontoxic. d. After 1970, studies showed that increasing concentrations of CFC’s in atmosphere is responsible for loss of ozone layer. THE END