Ch. 12 - Alkanes (sat’d HCs)

1. Ch. 12 - Alkanes (sat’d HCs)

2. Alkanes • Acyclic Saturated Hydrocarbons (chains) • General Formula: CnH2n+2 • Structural: (ex.: C4H10) • Complete • Condensed • Skeletal • Line Angle Decomposition of plant and animal matter in marshes is a good source of methane gas.

3. Alkane Nomenclature • Methane • Ethane • Propane • Butane • Pentane • Hexane • Heptane • Octane • Nonane • Decane

4. Alkane Isomerism • Isomers: compounds that share the same molecular formula but have different structural formulas • With an increased number of C atoms, there is an exponentially increased number of isomers • Constitutional - same molecular formula, different structural formula; differ in connectivity of atoms • Ex. C4H10 butane ; isobutane • Ex. C8H18 octane; 3-methyl heptane

5. Alkyl Groups & IUPAC names • Use the following rules to properly name hydrocarbon molecules: • 1. Identify the longest, continuous chain of C atoms and name it (parent C chain and suffix. • 2. # the C atoms in the chain from the end nearest an alkyl group. • 3. # and name the attached alkyl group(s). • 4. If more than one alkyl group: • 1st substituent must have lower number. • Alkyl groups are listed in alphabetical order. • If two or more identical substituents are bonded, use prefixes to indicate how many • 5. Separate #s from each other with commas; separate names from numbers with hyphens; do not use a hyphen/space after the last substituent, before the parent alkane name. • Carbons are classified 4 ways in a chain: • Primary, secondary, tertiary, quaternary • Based on the # of C atoms to which the carbon atom is bonded.

6. Branched-chain Alkyl Groups • “Simple”: 4 important ones to know! • Complex: “select the longest chain as the “base” alkyl, add “substituents.” • Ex.

7. Cycloalkanes

8. Isomerism of Cycloalkanes • Constitutional (ex.: C5H10) 5 isomers • Stereoisomers: possible with substituted cycloalkanes (ex.: 1,2-Dimethylcyclohexane) • Cis- (SAME side) • Trans- (ACROSS from)

9. Sources of Saturated Hydrocarbons • Natural Gas: • Methane (50-90%) • Ethane (1-10%) • Propane & Butane (up to 8%) • Petroleum (crude oil): this is a complex mixture of both cyclic and acyclic hydrocarbons which can be separated by a process known as fractional distillation.

10. Physical Properties of Hydrocarbons • All are insoluble in water • Consider the polarity of the compounds • Therefore they can make good protective coatings • All are less dense than water (0.6-0.8 g/mL) • Oil & water • Boiling Points & States of Matter • Generally, BP increases with increasing # C atoms • Reason: increasing LDF • 1-4 C atoms = gas; 5-17 C atoms = liquid; >17 C atoms = solid • Isomers: Branched BP < Unbranched BP • Cyclic Compounds have higher BP than Acyclic.

11. Chemical Properties of Hydrocarbons • Alkanes are the least reactive organic compounds (they have no fcn’l groups). However, two major reactions are common: • Combustion • R (some hydrocarbon) + O2 → CO2 + H2O + energy • very exothermic reaction. • If the quantity of O2 is insufficient, it will form a poison called carbon monoxide (CO). • Here is an example with methane: CH4 + 2 O2 → CO2 + 2 H2O with less O2: 2 CH4 + 3 O2 → 2 CO + 4 H2O (poison!) with even less O2: CH4 + O2 → C + 2 H2O (black soot forms) • Halogenation • R-H + X2 --> R-X + H-X

12. Hydrocarbon fuels • Fossil fuels (solid, liquid, or gas) form from organic material being covered by successive layers of sediment over millions of years • Oil & natural gas: slow decomposition & burying of marine phytoplankton& zooplankton that sank to the sea floor.  • Coal: ancient swamps and bogs - slow decomposition of land plants in anaerobic conditions: • e.g. peat bogs of Ireland

13. Petroleum, Naphtha, or crude oil • From Greek petra = rock and oleum = oil • Thick, dark brown or greenish liquid • Complex mixture of various hydrocarbons, largely of the alkane series • May vary much in appearance, composition, and purity • Petroleum is also the raw material for many chemical products: fuels & solvents • Can be altered into: fertilizers, pesticides, and plastics • Think of the impact of a substantial oil crisis on our economy & society!

14. A rock formation such as this is necessary for the accumulation of petroleum and natural gas.

15. Crude Oil History • 1st oil wells drilled in China in 4th century depth • up to 800 ft. • Drilled using bits attached to bamboo poles • Burned oil to evaporate brine & produce salt. • 10th century, bamboo pipelines connected oil • wells with salt springs.

16. Ancient Persian tablets indicate the medicinal and lighting uses of petroleum in the upper society. 8th century: streets of Baghdad paved with tar. In the 9th century, oil fields were exploited in Baku, Azerbaijan, to produce naphtha.

17. Discovery of oil in 1859, near Titusville, Pennsylvania. Great demand for kerosene and oil lamps. Medicinal purposes, lighting, and lubricants for new steam engines. Introduction of internal combustion engine lead to major "oil booms" in Texas, Oklahoma, and California.

18. The complex hydrocarbon mixture present in petroleum is separated into simpler mixtures by means of a fractionating column. Differences in BPs of hydrocarbon chains can separate out sections of the crude oil: Fractional Distillation

20. Octane: major component of gasoline • Octane is an alkane hydrocarbon:CH3(CH2)6CH3. • octane isomer: 2,2,4-Trimethylpentane = 100 pts • on the octane rating scale • n-heptane is the zero point (greatest engine knocking • or “pinging”) • Octane ratings are used to represent antiknock • performance (less premature combustion)

21. Natural gas • Natural gas mainly methane (does contain other “small” HC cpds). • Highly flammable • No ash and very little air pollution. • From light portion of petroleum • Rises thru fissures in earth’s crust • Man-made wells can tap it • Discovered thousands of years ago could be burned for heat and light. • Colorless, odorless, & lighter than air. • Mercaptan, chemical odorant, is added for gas leaks. • natural gas combustion  CO2 + H2O • Natural gas found in different underground formations: shale, sandstone beds, coal seams, & deep, salt water aquifers

22. New sources of methane gas: Decomposition of organic matter in landfills CH4 gas can be tapped instead of vented

23. 3 lakes contain large concentrations of dissolved CO2 gas. Kivu Lake Lake Nyos & Lake Monoun sites of gas explosions: 40 dead at Monoun & 1800 at Nyos 3rd lake is Kivu, which contains a 1,000x more gas than Lake Nyos.

24. Coal formation • Vegetable matter accrues • Prevented from decay • Forms peat beds. • Over time: buried & • compressed, forms lignite. • Increased P & T makes bituminous coal (higher C content). • At great depths, high temps • reduce CH4 & forms • anthracite (very high in C)

25. Current Consumption? What about as China and India modernize? These countries have 33% of world population! Fossil Fuel “Facts” Source: Shell Oil The U.S. has 4% of the World's population. The U.S. uses 34% of Earth's natural resources.

26. U.S. Sources of Energy Production Fossil Fuels 86% Geothermal 0.5% Nuclear 8% Wind Farms 0.1% Hydroelectric 2% Solar 0.1% Biofuels 3.3% source: US Dept of Energy Remember that, while hydrocarbons serve as a transportation fuel, they are also used to produce plastics, etc. Enormous dependence on a limited resource. Other alternatives? -Wave energy -Tidal energy -New technology for solar panels, turbines, etc. -Conservation!! -Efficiency!!!

27. Problems associated with alkane hydrocarbons • Hydrocarbonpollution: (oil spills) of aquatic environments (e.g. BP in the Gulf of Mexico) • Global warming: CO2 and H2O • Acid rain due to sulfur impurities in oil and coal: damage crops, lakes, buildings, etc. • Smog and soot: increase respiratory problems • Land fill: non-decomposing plastics • Ozone depletion / increased UV radiation

28. Accidental & Purposeful Oil Spills Clean-up takes into account density and non-polar nature

29. Global warming: The Greenhouse effect: Short wavelength solar radiation releases energy as it hits molecules. Turns into long wavelength energy. Gases in atmosphere trap it and warm the atmosphere.

30. Arctic ice sheet 1979 and 2000 CO2 increase correlates to average global temperature increase Can cause: changes in sea level, reduction of reflective ice caps, increased storm ferocity, plant & animal re-distribution, shift ocean currents, create droughts & forest fires, increased short-term temperature fluctuations.

31. Alkane substitution reaction:Incoming atom or group of atoms (orange sphere) replaces a hydrogen atom in the alkane model. • Naming: • Treat halogen atoms like alkyl groups. • F = fluoro; Cl = chloro; Br = bromo; I = iodo • Ex.: CH3-CHBr-CHBr-CHI-CH2-CH3

32. Halogenation Reactions General equation: RH + X2 → RX + HX Hydrocarbon + Halogen  Halogenated + acid (diatomic) hydrocarbon Ex. CH4 + Cl2 --> CH3Cl + HCl Highly exothermic reaction: can lead to an explosion

33. The process can continue to alter the resulting products as long as the halogen remains in sufficient quantities to drive further reactions. (The halogen would be the __________ reactant.)

34. Space-filling models of the four ethyl halides. Do these molecules act as polar or non-polar?

35. Chlorofluorocarbons (CFCs) • Developed in the 1930's • Very stable compounds composed of C, F, Cl, & H • Freon is the tradename: • Trichlorofluoromethane • Dichlorodifluoromethane Trichloro-trifluoroethane Dichloro-tetrfluoroethane Chloropentafluoroethane

36. Safe, non-toxic, non-flammable alternative to dangerous substances (e.g. ammonia) for aerosol-spray propellants, refrigerants, solvents, and foam-blowing agents

37. CFCs and refrigeration CFCs and propellants

38. UV radiation in the stratosphere

39. The Ozone Layer Chemistry CFCl3 + UV Light ==> CFCl2 + Cl Cl + O3 ==> ClO + O2 ClO + O ==> Cl + O2 The chlorine free radical atom is then able to attack another ozone molecule Cl + O3 ==> ClO + O2 ClO + O ==> Cl + O2 and again ... Cl + O3 ==> ClO + O2 ClO + O ==> Cl + O2 and again... thousands of times! A catalyst!

40. The ozone destruction process requires conditions cold enough (-80oC) for stratospheric clouds to form. Once these stratospheric clouds form the process can take place, even in warmer conditions

41. Ozone consumption has been greatly reduced, however CFCs may linger for another 150 years in the atmosphere 1997 ozone hole 2003 ozone hole Ozone layer thickness

42. What do you need to know (about saturated hydrocarbons)? • Structural characteristics (know the functional group) • Substituents • Nomenclature (the rules for naming the molecules) • Physical and Chemical properties (basic/simple) • Occurrence and uses (common) • Preparation (what basic reactions produce the molecules) • Characteristic reactions of the molecules