2 Alkanes Acyclic Saturated Hydrocarbons (chains) General Formula: CnH2n+2Structural: (ex.: C4H10)CompleteCondensedSkeletalLine AngleDecomposition of plant and animal matter in marshes is a good source of methane gas.
4 Alkane IsomerismIsomers: compounds that share the same molecular formula but have different structural formulasWith an increased number of C atoms, there is an exponentially increased number of isomersConstitutional - same molecular formula, different structural formula; differ in connectivity of atomsEx. C4H10 butane ; isobutaneEx. 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 many5. 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, quaternaryBased 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.
8 Isomerism of Cycloalkanes Constitutional (ex.: C5H10) 5 isomersStereoisomers: 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 waterConsider the polarity of the compoundsTherefore they can make good protective coatingsAll are less dense than water ( g/mL)Oil & waterBoiling Points & States of MatterGenerally, BP increases with increasing # C atomsReason: increasing LDF1-4 C atoms = gas; 5-17 C atoms = liquid; >17 C atoms = solidIsomers: Branched BP < Unbranched BPCyclic 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:CombustionR (some hydrocarbon) + O2 → CO2 + H2O + energyvery 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 H2Owith less O2:2 CH4 + 3 O2 → 2 CO + 4 H2O (poison!)with even less O2:CH4 + O2 → C + 2 H2O (black soot forms)HalogenationR-H + X2 --> R-X + H-X
12 Hydrocarbon fuelsFossil fuels (solid, liquid, or gas) form from organic material being covered by successive layers of sediment over millions of yearsOil & 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 IrelandFossil fuels supply over 80% of the world’s energy needs .All fossil fuels, whether solid, liquid, or gas, are the result of organic material being covered by successive layers of sediment over the course of millions of years. Oil and natural gas were formed from the slow decomposition and burying of planktonic marine plants and animals that sank to the muds of the sea floor. World crude oil reserves are estimated at more than one trillion barrels, of which the 11 OPEC Member Countries hold more than 75 per cent.According to the reference case of OPEC's World Energy Model (OWEM), total world oil demand in 2000 is put at 76 million barrels per day, As world economic growth continues, crude oil demand will also rise to 90.6m b/d in 2010 and 103.2m b/d by 2020.Oil provides about 40 percent of the energy Americans consume and 97 percent of U.S. transportation fuels.
13 Petroleum, Naphtha, or crude oil From Greek petra = rock and oleum = oilThick, dark brown or greenish liquidComplex mixture of various hydrocarbons,largely of the alkane seriesMay vary much in appearance, composition, andpurityPetroleum is also the raw material for many chemical products: fuels & solventsCan be altered into: fertilizers, pesticides, and plasticsThink of the impact of a substantial oil crisis on our economy & society!Crude oil is pumped from the ground in the Middle East (e.g., Saudi Arabian Arab Light), West Africa (e.g., Nigerian Bonny Light), the Americas, and Asia (Russia)Crude oils and most of their distillation products are extremely complex mixtures of organic chemicals with hydrocarbons being the most numerous and abundant (comprising more than 75 percent of most crude and fuel oils). Over 200 hydrocarbons, 90 sulfur‑containing organic compounds, and 33 nitrogen‑containing organic compounds are present in crude oils. In addition, there are porphyrins, sulfur, trace metals, and residues called asphaltenes in many crude oils. Crude oils and most crude oil products contain a series of n‑alkanes with chain lengths of carbon atoms numbering between 1 and 60. The ratio of abundance of odd chain lengths to even chain lengths is approximately 1.0. A series of branched alkanes are also present including isoprenoid alkanes such as pristane, farnesane, and phytane, naphthenes (cyclic alkanes with or without side chains), aromatic hydrocarbons (ranging from alkyl substituted benzenes and naphthalenes to polynuclear aromatic structures), and naphthenoaromatics (naphthenes joined with aromatic ring systems). Alkenes (olefins) are not usually present in crude oils but they are formed in some refining processes and are present in some refined products.A widely believed myth is that the oil itself is flammable, however it is actually the gas that evaporates from the oil that is flammable. Petroleum exists in the upper strata of some areas of the Earth's crust. Another name is naphtha, from Persian naft or nafátá (to flow).
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 polesBurned oil to evaporate brine & produce salt.10th century, bamboo pipelines connected oilwells with salt springs.The first oil wells were drilled in China in the 4th century or earlier. They had depth of up to 800 feet and were drilled using bits attached to bamboo poles. The oil was burned to evaporate brine and produce salt. By the 10th century, extensive bamboo pipelines connected oil wells with salt springs. Ancient Persian tablets indicate the medicinal and lighting uses of petroleum in the upper echelons of their society.In the 8th century, the streets of the newly-constructed Baghdad were paved with tar, derived from easily-accessible petroleum from natural fields in the region. In the 9th century, oil fields were exploited in Baku, Azerbaijan, to produce naphtha. These fields were described by the geographer Masudi in the 10th century, and by Marco Polo in the 13th century, who described the output of those wells as hundreds of shiploads. (See also: Timeline of Islamic science and technology.)The modern history of oil began in 1853, with the discovery of the process of oil distillation. Crude oil was distilled into kerosene by Ignacy Lukasiewicz, a Polish scientist. The first "rock oil" mine was created in Bobrka, near Krosno in southern Poland in the following year and the first refinery (actually a distillery) was built in Ulaszowice, also by Lukasiewicz. These discoveries rapidly spread around the world, and Meerzoeff built the first Russian refinery in the mature oil fields at Baku in 1861.Oil field in California, 1938The first modern oil well was drilled in 1848 by Russian engineer F.N. Semyenov, on the Aspheron Peninsula north-east of Baku.The first commercial oil well drilled in North America was in Oil Springs, Ontario, Canada in 1858, dug by James Miller Williams. The American petroleum industry began with Edwin Drake's discovery of oil in 1859, near Titusville, Pennsylvania. The industry grew slowly in the 1800s, driven by the demand for kerosene and oil lamps. It became a major national concern in the early part of the 20th century; the introduction of the internal combustion engine provided a demand that has largely sustained the industry to this day. Early "local" finds like those in Pennsylvania and Ontario were quickly exhausted, leading to "oil booms" in Texas, Oklahoma, and California.
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 tomajor "oil booms" in Texas,Oklahoma, and California.The modern history of oil began in 1853, with the discovery of the process of oil distillation. Crude oil was distilled into kerosene by Ignacy Lukasiewicz, a Polish scientist. The first "rock oil" mine was created in Bobrka, near Krosno in southern Poland in the following year and the first refinery (actually a distillery) was built in Ulaszowice, also by Lukasiewicz. These discoveries rapidly spread around the world, and Meerzoeff built the first Russian refinery in the mature oil fields at Baku in 1861.Oil field in California, 1938The first modern oil well was drilled in 1848 by Russian engineer F.N. Semyenov, on the Aspheron Peninsula north-east of Baku.The first commercial oil well drilled in North America was in Oil Springs, Ontario, Canada in 1858, dug by James Miller Williams. The American petroleum industry began with Edwin Drake's discovery of oil in 1859, near Titusville, Pennsylvania. The industry grew slowly in the 1800s, driven by the demand for kerosene and oil lamps. It became a major national concern in the early part of the 20th century; the introduction of the internal combustion engine provided a demand that has largely sustained the industry to this day. Early "local" finds like those in Pennsylvania and Ontario were quickly exhausted, leading to "oil booms" in Texas, Oklahoma, and California.
18 Fractional Distillation The complex hydrocarbon mixture present in petroleum is separated into simpler mixtures by means of a fractionating column.Differences in BPs ofhydrocarbon chainscan separate outsections ofthe crude oil:Fractional DistillationCrude oil is measured in barrels. When crude oil first came into large-scale commercial use in the United States in the 19th century, it was stored in wooden barrels. One barrel equals 42 US gallons, or 159 litres.Cracking reactions"Cracking" breaks larger molecules into smaller ones. This can be done with a thermic or catalytic method. The thermal cracking process follows a homolytic mechanism, that is, bonds break symmetrically and thus pairs of free radicals are formed. The catalytic cracking process involves the presence of acid catalysts (usually solid acids such as silica-alumina and zeolites) which promote a heterolytic (asymmetric) breakage of bonds yielding pairs of ions of opposite charges, usually a carbocation and the very unstable hydride anion. Carbon-localized free radicals and cations are both highly unstable and undergo processes of chain rearrangement, C-C scission in position beta (i.e., cracking) and intra- and intermolecular hydrogen transfer or hydride transfer. In both types of processes, the corresponding reactive intermediates (radicals, ions) are permanently regenerated, and thus they proceed by a self-propagating chain mechanism. The chain of reactions is eventually terminated by radical or ion recombination.Here is an example of cracking with butane CH3-CH2-CH2-CH31st possibility (48%): breaking is done on the CH3-CH2 bond.CH3* / *CH2-CH2-CH3after a certain number of steps, we will obtain an alkane and an alkene: CH4 + CH2=CH-CH32nd possibility (38%): breaking is done on the CH2-CH2 bond.CH3-CH2* / *CH2-CH3after a certain number of steps, we will obtain an alkane and an alkene from different types: CH3-CH3 + CH2=CH23rd possibility (14%): breaking of a C-H bondafter a certain number of steps, we will obtain an alkene and hydrogen gas: CH2=CH-CH2-CH3 + H2
19 Residential heating oil 34.74 149,690 Gasahol 28.06 120,900 93 to 94 Fuel type Mega Joules / Liter BTU / US gal Research octane #Gasoline29.0125,00091 to 98Diesel fuel oil32.19138,690N/AResidential heating oil34.74149,690Gasahol10% ethanol90% gasoline28.06120,90093 to 94fuel type MJ/L BTU/imp gal BTU/US gal Research octane number (RON)LPG , ,Ethanol , ,Methanol , ,
20 Octane: major component of gasoline Octane is an alkane hydrocarbon:CH3(CH2)6CH3.octane isomer: 2,2,4-Trimethylpentane = 100 ptson the octane rating scalen-heptane is the zero point (greatest engine knockingor “pinging”)Octane ratings are used to represent antiknockperformance (less premature combustion)Octane is an alkane hydrocarbon with the chemical formula CH3(CH2)6CH3. It has many isomers.One of the isomers, iso-octane or 2,2,4-Trimethylpentane, is of major importance, as it has been selected as the 100 point on the octane rating scale, with n-heptane as the zero point. Octane ratings are ratings used to represent the anti-knock performance of petroleum-based fuels (Octane is less likely to prematurely combust under pressure than heptane), given as the percentage of 2,2,4-trimethylpentane in an 2,2,4-trimethylpentane / n-heptane mixture that would have the same performance. It is an important constituent of gasoline.
21 Natural gasNatural gas mainly methane (does contain other “small” HC cpds).Highly flammableNo ash and very little air pollution.From light portion of petroleumRises thru fissures in earth’s crustMan-made wells can tap itDiscovered 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 + H2ONatural gas found in different underground formations: shale, sandstone beds, coal seams, & deep, salt water aquifersGas is a collective term for one of three types of matter. The other two are solid and liquid. Gas has no set shape or volume. Solids have well defined shapes and are difficult to compress. Liquids are free flowing and bounded by self-formed surfaces. Gases expand to fill their containers and have a lower density than liquids or solids.Natural gas is clean burning, easy to transport, convenient to use, and in abundant supply. It can be used:in the home for heating, hot water and cooking,commercially for catering, drying and heating purposes,industrially for manufacturing and processing,for power generation in power station turbines and cogeneration plants, andin transportation as a fuel for vehicles such as buses.Natural gas is found in porous rock formations beneath the surface of the earth. Natural gas should not be confused with, liquified natural gas (LNG), liquified petroleum gas (LPG), or town gas.Liquified natural gas (LNG), is made by chilling natural gas to minus 160 C. It is then stored in special cylinders which makes shipping LNG to other countries an easier task.Liquified petroleum gas (LPG) is a by-product of oil and gas production. LPG is made of propane or butane or a mixture of these gases. These turn into liquid under pressure and are then stored in cylinders or tanks. When the pressure is released, the liquid becomes a gas. Each year Australia exports one million tonnes of LPG.Town gasIn the olden days, town gas, often called manufactured or coal gas, was often made by baking coal in large airtight ovens (gas retorts). The gas bubbles from the hot coals were piped off and used as a household fuel. Natural gas has replaced town gas.Properties and characteristicsNatural gas is non-toxic before combustion, and the exhaust product from approved appliances is also non-toxic, provided equipment is properly maintained.Natural gas is comprised of mostly methane (approx. 85%-90%) and lesser amounts of ethane (5%-15%), carbon dioxide (2%), nitrogen (1%-2%) and propane (0.2%).The natural gas flammability range - air/gas volume ratio - varies between 5:1 and 15:1. For stoichiometric combustion the air/gas volume is 9.91:1.Natural gas has an approximate auto-ignition temperature in air of 537°C - 680°C (dependent on air /gas composition and atmospheric pressure) and a flame speed of 0.4 metres per second. Natural gas has a relative density to air of 0.62.Natural gas was formed millions of years ago when most of the earth was covered by water. Plant and tiny animal remains were mixed and layered with sand and mud. When the Earth underwent natural but drastic changes to form today’s landscape, the intense heat and pressure transformed these fossils into hydrocarbons—chemical compounds of hydrogen and carbon atoms. Natural gas is made up mainly of a chemical called methane, a simple, compound that has a carbon atom surrounded by four hydrogen atoms. Methane is highly flammable and burns almost completely. There is no ash and very little air pollution. Depending on the arrangement of the atoms, what were once sea plants and animals are now natural gas or crude oil deposits contained in the earth’s crust. Natural gas (a combustible, gaseous mixture of simple hydrocarbons) is a very light portion of petroleum, which includes both natural gas and crude oil. Natural gas may rise to the surface through natural openings in the earth’s crust or can be brought to the surface through man-made wells. Humans discovered thousands of years ago that this naturally occurring resource could be burned and used for heat and light.In its natural state you can’t see or smell natural gas. It is colorless, odorless and lighter than air. Mercaptan, a chemical odorant, is added to natural gas so it can be smelled if it leaks. Natural gas is made up mostly of methane, which has a simple hydrocarbon structure of one carbon atom and four hydrogen atoms (CH4). This means it burns easily and emits less pollution. When natural gas is burned, it produces mostly carbon dioxide and water vapor.Natural gas can be found in a variety of different underground formations, including: shale formations, sandstone beds, coal seams, and deep, salt water aquifers (underground ponds of water).
22 New sources of methane gas: Decomposition of organic matter in landfillsCH4 gas can be tappedinstead of vented
23 Kivu Lake 3 lakes contain large concentrations of dissolved CO2 gas. Lake Nyos & Lake Monoun sites of gasexplosions: 40 dead at Monoun & 1800 at Nyos3rd lake is Kivu,which containsa 1,000x moregas than Lake Nyos.3 lakes in the world containlarge concentrationsof dissolved gas.Lake Nyos & Lake Monoun in Cameroon sites of gas explosions 40 deaths at Monoun and 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 tempsreduce CH4 & formsanthracite (very high in C)Coal is derived from the accumulation of partially decayed land plants. As the sediment solidifies into rock, the organic material decomposes under the influence of great pressure and high temperature. The burning of fossil fuels for energy is a major source of air pollution, contributing in particular to acid rain and the greenhouse effect.
25 What about as China and India modernize? CurrentConsumption?What about as China and Indiamodernize?These countries have 33% of world population!Fossil Fuel “Facts”Source: Shell OilThe 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 EnergyRemember 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 Hydrocarbon pollution: (oil spills) of aquatic environments (e.g. BP in the Gulf of Mexico)Global warming: CO2 and H2OAcid rain due to sulfur impurities in oil and coal: damage crops, lakes, buildings, etc.Smog and soot: increase respiratory problemsLand fill: non-decomposing plasticsOzone depletion / increased UV radiationThe greenhouse gasesWater vapor (H2O) causes about 60% of Earth's naturally-occurring greenhouse effect. Other gases influencing the effect include carbon dioxide (CO2) (about 26%), methane (CH4), nitrous oxide (N2O) and ozone (O3) (about 8%). Collectively, these gases are known as greenhouse gases.the residence time for water vapor in the atmosphere is short (about a week) so perturbations to water vapor rapidly re-equilibriate. In contrast, the lifetimes of CO2, methane, etc, are long (hundreds of years) and hence perturbations remain. Thus, in response to a temperature perturbation caused by enhanced CO2, water vapor would increase, resulting in a (limited) positive feedback and higher temperatures. In response to a perturbation from enhanced water vapor, the atmosphere would re-equilibriate due to clouds causing reflective cooling and water-removing rain
28 Accidental & Purposeful Oil Spills Clean-up takes into account density and non-polar nature
29 Global warming: The Greenhouse effect: Short wavelengthsolar radiationreleases energyas it hits molecules.Turns into longwavelength energy.Gases in atmospheretrap it and warm the atmosphere.Many of the hottest years on record are recent ones.Sea levels are slowly increasing, threatening cities such as Venice, ItalySea level as measured at San Francisco, California, USA.Coastal ocean temperatures are so high that sea corals are being killed globally.Glaciers are in retreat all over the world.In Canada, polar bears are starving because Hudson's Bay is ice-free too long each year so they cannot catch enough seals to survive.Also in Canada, river temperatures are so high now that salmon are being killed on their way to their spawning grounds - thus killing off the salmon FOREVER. (* NEW *)Frogs are dying all over the world - not just a few frogs here and there but WHOLE SPECIES are dying off FAST.Plants are germinating earlier and earlier and moving farther and farther North.Louisiana (USA) is losing land at a rate of about 25 square miles per year.This effect has now been shown to be primarily due to subsidence ofthe land. A new NOAA report says that the northern part of the Gulfof Mexico is sinking at a rate of 60 inches per century or about 0.6 inchesper year (whereas sealevel is only rising by 8 inches per century). (* NEW *)The Arctic and Antarctic are warming.Increases in droughts and forest fires.Animal ranges are changing due to changes in the local climates.Temperature hit 100 in London (August 10, 2003) for the first time in recorded history.Over 90% of the ice shelf north of Ellesmere Island (Canada) is gone.Alaska dataAverage temperature has risen 7 degrees in the last 30 years.The sea level around Alaska has risen a foot in the last century.The permafrost is melting - which is causing buildings to sink into the mud.98% of glaciers & sea ice are melting.Scary pictures of the northern polar regions in 1979 & 2000 Polar ice has been decreasing by 1% per year since 1979.
30 Arctic ice sheet 1979 and 2000CO2 increase correlates to average global temperature increaseCan cause: changes in sea level,reduction of reflective ice caps,increased storm ferocity,plant & animal re-distribution,shift ocean currents, createdroughts & forest fires, increasedshort-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 = iodoEx.: CH3-CHBr-CHBr-CHI-CH2-CH3
32 Halogenation Reactions General equation: RH + X2 → RX + HXHydrocarbon + Halogen Halogenated + acid (diatomic) hydrocarbonEx. CH4 + Cl2 --> CH3Cl + HClHighly exothermic reaction: can lead to an explosionHalogenation reactionRH + X2 → RX + HXThese are the steps when methane is chlorinated. This is a highly exothermic reaction that can lead to an explosion.1. Initiation step: splitting of a chlorine molecule to form two chlorine atoms. A chlorine atom has an unpaired electron and acts as a free radical.Cl2 → Cl* / *Cl energy provided by UV.2. Propagation (two steps): a hydrogen atom is pulled off from methane then the methyl pulls a Cl from Cl2CH4 + Cl* → CH3* + HClCH3* + Cl2 → CH3Cl + Cl*This results in the desired product plus another Chlorine radical. This radical will then go on to take part in another propagation reaction causing a chain reaction. If there is an excess of Chlorine, other products like CH2Cl2 may be formed.3. Termination step: recombination of two free radicalsCl* + Cl* → Cl2, orCH3* + Cl* → CH3Cl, orCH3* + CH3* → C2H6.The last possibilty in the termination step will result in an impurity in the final mixture; notably this results in an organic molecule with a longer carbon chain than the reactants.
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'sVery stable compounds composed of C, F, Cl, & HFreon is the tradename:TrichlorofluoromethaneDichlorodifluoromethaneChlorofluorocarbons (CFCs) are a family of chemical compounds developed back in the 1930's as safe, non-toxic, non-flammable alternative to dangerous substances like ammonia for purposes of refrigeration and spray can propellants. Their usage grew enormously over the years. One of the elements that make up CFCs is chlorine. Very little chlorine exists naturally in the atmosphere. But it turns out that CFCs are an excellent way of introducing chlorine into the ozone layer. The ultraviolet radiation at this altitude breaks down CFCs, freeing the chlorine. Under the proper conditions, this chlorine has the potential to destroy large amounts of ozone. This has indeed been observed, especially over Antarctica. As a consequence, levels of genetically harmful ultraviolet radiation have increased.Chlorofluorocarbons (CFCs) are highly stable compounds that are used as propellents in spray cans and in refrigeration units. They are several organic compounds composed of carbon, fluorine, chlorine, and hydrogen. CFCs are manufactured under the trade name Freon (q.v.). Developed during the 1930s, CFCs found wide application after World War II. These halogenated hydrocarbons, notably trichlorofluoromethane (CFC-11, or F-11) and dichlorodifluoromethane (CFC-12, or F-12), have been used extensively as aerosol-spray propellants, refrigerants, solvents, and foam-blowing agents. They are well-suited for these and other applications because they are nontoxic and nonflammable and can be readily converted from a liquid to a gas and vice versa.Chlorofluorocarbons or CFCs (also known as Freon) are non-toxic, non-flammable and non-carcinogenic. They contain fluorine atoms, carbon atoms and chlorine atoms. The 5 main CFCs include CFC-11 (trichlorofluoromethane - CFCl3), CFC-12 (dichloro-difluoromethane - CF2Cl2), CFC-113 (trichloro-trifluoroethane - C2F3Cl3), CFC-114 (dichloro-tetrfluoroethane - C2F4Cl2), and CFC-115 (chloropentafluoroethane - C2F5Cl).CFCs have been found to pose a serious environmental threat. Studies undertaken by various scientists during the 1970s revealed that CFCs released into the atmosphere accumulate in the stratosphere, where they had a deleterious effect on the ozone layer. Stratospheric ozone shields living organisms on Earth from the harmful effects of the Sun's ultraviolet radiation; even a relatively small decrease in the stratospheric ozone concentration can result in an increased incidence of skin cancer in humans and in genetic damage in many organisms. In the stratosphere the CFC molecules break down by the action of solar ultraviolet radiation and release their constituent chlorine atoms. These then react with the ozone molecules, resulting in their removal.CFCs have a lifetime in the atmosphere of about 20 to 100 years, and consequently one free chlorine atom from a CFC molecule can do a lot of damage, destroying ozone molecules for a long time. Although emissions of CFCs around the developed world have largely ceased due to international control agreements, the damage to the stratospheric ozone layer will continue well into the 21st century.Trichloro-trifluoroethaneDichloro-tetrfluoroethaneChloropentafluoroethane
39 The Ozone Layer Chemistry CFCl3 + UV Light ==> CFCl2 + ClCl + O3 ==> ClO + O2ClO + O ==> Cl + O2The chlorine free radical atomis then able to attack anotherozone moleculeand again ...and again... thousands of times!A catalyst!One billion years ago, early aquatic organisms called blue-green algae began using energy from the Sun to split molecules of H2O and CO2 and recombine them into organic compounds and molecular oxygen (O2). This solar energy conversion process is known as photosynthesis. Some of the photosynthetically created oxygen combined with organic carbon to recreate CO2 molecules. The remaining oxygen accumulated in the atmosphere, touching off a massive ecological disaster with respect to early existing anaerobic organisms. As oxygen in the atmosphere increased, CO2 decreased. High in the atmosphere, some oxygen (O2) molecules absorbed energy from the Sun's ultraviolet (UV) rays and split to form single oxygen atoms. These atoms combined with remaining oxygen (O2) to form ozone (O3) molecules, which are very effective at absorbing UV rays. The thin layer of ozone that surrounds Earth acts as a shield, protecting the planet from irradiation by UV light. The amount of ozone required to shield Earth from biologically lethal UV radiation, wavelengths from 200 to 300 nanometers (nm), is believed to have been in existence 600 million years ago. At this time, the oxygen level was approximately 10% of its present atmospheric concentration. Prior to this period, life was restricted to the ocean. The presence of ozone enabled organisms to develop and live on the land. Ozone played a significant role in the evolution of life on Earth, and allows life as we presently know it to exist.Ozone is produced naturally in the stratosphere when highly energetic solar radiation strikes molecules of oxygen, O2, and cause the two oxygen atoms to split apart in a process called photolysis.
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 conditionsAs temperatures in the lower stratosphere cools below -80'C, Polar Stratospheric Clouds (PSC's) start to form.In the area over Antarctica, there are stratospheric cloud ice particles that are not present at warmer latitudes. Reactions occur on the surface of the ice particles that accelerate the ozone destruction caused by stratospheric chlorine. Polar regions get a much larger variation in sunlight than anywhere else, and during the 3 months of winter spend most of time in the dark without solar radiation. Temperatures hover around or below -80'C for much of the winter and the extremely low antarctic temperatures cause cloud formation in the relatively ''dry''stratosphere. These Polar Stratospheric Clouds (PSC's) are composed of ice crystals that provide the surface for a multitude of reactions, many of which speed the degredation of ozone molecules. This phenomenon has caused documented decreases in ozone concentrations over Antarctica.In fact, ozone levels drop so low in spring in the Southern Hemisphere that scientists have observed what they call a "hole" in the ozone layer. The ozone destruction process requires conditions cold enough for stratospheric clouds to form. Once these stratospheric clouds form the process can take place, even in warmer conditions.It was first noticed by a research group from The British Antarctic Survey in the 1970's. Joseph Farman, Brian Gardiner and Jonathan Shanklin, are the BAS scientists who discovered the Antarctic ozone hole. In the 1980's the first measurements of this loss were actually documented. In 1984, when the British first reported their findings, October ozone levels were about 35 percent lower than the average for the 1960s. When the first measurements were taken the drop in ozone levels in the stratosphere was so dramatic that at first the scientists thought their instruments were faulty.The U.S. satellite Nimbus-7 quickly confirmed the results, and the term Antarctic ozone hole entered popular language. More recently an ozone hole has appeared over the North Pole. The ozone hole appeared first over the colder Antarctic because the ozone-destroying chemical process works best in cold conditions. The Antarctic continent has colder conditions than the Arctic, which has no land-mass. As the years have gone by the Ozone Hole has increased rapidly and is as large as the Antarctica continent. The hole lasts for only two months, but its timing could not be worse. Just as sunlight awakens activity in dormant plants and animals, it also delivers a dose of harmful ultraviolet radiation. After eight weeks, the hole leaves Antarctica, only to pass over more populated areas, including The Falkland Islands, South Georgia and the tip of South America. This biologically damaging, high-energy radiation can cause skin cancer, injure eyes, harm the immune system, and upset the fragile balance of an entire ecosystem. News about the ozone hole that forms over Antarctica each October has spread around the world. The ozone hole can be as big as 1.5 times larger than the United States.However, less-well-known is that ozone depletion has been measured everywhere outside the tropics, and that it is, in fact, getting worse. in the middle latitudes (most of the populated world), ozone levels have fallen about 10% during the winter and 5% in the summer. Since 1979, they have fallen about 5% per decade when averaged over the entire year. Depletion is generally worse at higher latitudes, i.e. further from the Equator.
41 Ozone consumption has been greatly reduced, however CFCs may linger for another150 years in the atmosphere1997ozonehole2003ozoneholeOzone layer thickness
42 What do you need to know (about saturated hydrocarbons)? Structural characteristics (know the functional group)SubstituentsNomenclature (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