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Chapter 22 Hydrocarbon Compounds Organic Chemistry and Hydrocarbons Organic originally meant chemicals that came from organisms 1828 German chemist Friedrich Wohler synthesized urea in the lab Today, organic chemistry is the chemistry of virtually all compounds containing the element carbon Organic Chemistry and Hydrocarbons Over a million organic compounds, with a dazzling array of properties Why so many? Carbon’s unique bonding ability! Let’s start with the simplest of the organic compounds: Hydrocarbons Organic Chemistry and Hydrocarbons Hydrocarbons contain only two elements: hydrogen and carbon – simplest hydrocarbons called alkanes, which contain only single covalent bonds – methane (CH4) with one carbon is the simplest alkane. It is the major component of natural gas Models of Methane Organic Chemistry and Hydrocarbons Review structural formula- p. 698 Carbon has 4 valence electrons, thus forms 4 covalent bonds – not only with other elements, but also forms bonds WITH ITSELF. Ethane (C2H6) is the simplest alkane with a carbon to carbon bond Straight-Chain Alkanes Straight-chain alkanes contain any number of carbon atoms, one after the other, in a chain -meaning one linked to the next C-C-C Names C-C-C-C etc. of alkanes will always end with -ane Straight-Chain Alkanes Combined with the -ane ending is a prefix for the number of carbons – Table 22.1, page 700 Homologous series- a group of compounds that have a constant increment of change In alkanes, it is: -CH2- Alkane Hydrocarbons Name Methane Ethane Propane Butane Pentane Hexane Heptane Octane Nonane Decane Molecular Form CH4 C2H6 Alkane Prefixes – C3H8 The root indicates the C4H10 number of carbon atoms C5H12 C6H14 C7H16 C8H18 C9H20 C10H22 Straight-Chain Alkanes Many alkanes used for fuels: methane, propane, butane, octane As the number of carbons increases, so does the boiling and melting pt. – The first 4 are gases; #5-15 are liquids; higher alkanes are solids Condensed structural formulas? Note examples on page 702 Alkane Melting and Boiling Points Functional Groups Most organic chemistry involves replacing one or more of the hydrogen atoms with a ‘substituent group’ – Groups often contain C, O, N, S, or P – They are also called “functional groups”the chemically functional part of the molecule. They change the properties or function of the molecule. Alcohols Alcohols - a class of organic compounds with an -OH group –The -OH functional group in alcohols is called a “hydroxyl” group; thus R-OH is the formula How is this different from the hydroxide ion with basics? (covalent bonding with carbon- not ionic with a metal such as sodium) Methanol Structure Ethanol Ball and Stick Alcohols Both IUPAC and common names For IUPAC: –drop the -e ending of the parent alkane name; add ending of -ol, number the position of -OH –parent is the longest chain that contains the carbon with the hydroxyl attached. Alcohols Common names: –similar to halocarbons, meaning name the alkyl group followed by the word ‘alcohol’ –One carbon alcohol = methyl alcohol Properties of Alcohols Denatured alcohol- means it has been made poisonous by the addition of other chemicals, often methyl alcohol (methanol, or wood alcohol). As little as 10 mL of methanol has been known to cause permanent blindness, and 30 mL has resulted in death!!! Alkenes Multiple bonds can also exist between the carbon atoms Hydrocarbons containing carbon to carbon double bonds are called alkenes C=C C-C=C Called “unsaturated” hydrocarbons if they contain double or triple bonds Alkynes Hydrocarbons containing carbon to carbon triple bonds called alkynes -C C Alkynes are not plentiful in nature Simplest is ethyne- common name acetylene (fuel for torches) Table 22.5, page 715 for b.p. and m.p. Section 22.5 Hydrocarbons from the Earth OBJECTIVES: –Identify three important fossil fuels and describe their origins. Natural Gas Fossil fuels provide much of the world’s energy Natural gas and petroleum contain mostly aliphatic (straight-chain) hydrocarbons Natural gas is an important source of alkanes of low molecular mass Natural Gas Natural gas is typically: – 80% methane, 10% ethane, 4% propane, and 2% butane with the remainder being nitrogen and higher molar mass hydrocarbons – also contains a small amount of He, that is recovered and used in various industries, including balloons Natural Gas Natural gas is prized for combustion, because with adequate oxygen, it burns with a hot, clean blue flame: CH4 + 2O2 → CO2 + 2H2O + heat Insufficient burning has a yellow flame, due to glowing carbon parts, as well as making carbon monoxide Petroleum The compounds found in petroleum (or crude oil) are more complex than those in natural gas Usually straight-chain and branched-chain alkanes, with some aromatic compounds also Crude oil must be refined (separated) before being used Petroleum Fractional Distillation Crude Oil Components Petroleum It is separated by distillation into fractions, according to boiling pt. Fractions containing higher molar mass can be “cracked” into more useful shorter chain components, such as gasoline and kerosene – involves catalyst and heat – starter materials for plastics and paints Petroleum Cracking Coal From huge fern trees and mosses decaying millions of years ago under great pressure Stages in coal formation: 1. Peat- soft, fibrous material much like decayed garden refuse; high water content. After drying will make a low-cost, smoky fuel Coal 2. Lignite- peat left in the ground longer, loses it’s fibrous texture, and is also called brown coal – harder than peat; higher C content (50%); still has high water content 3. Bituminous, or soft coal- formed after more time; lower water content, higher C content (70-80%) Coal 4. Anthracite, or hard coal – carbon content exceeding 80%, making it an excellent fuel source Coal may be found close to the surface (strip-mined), or deep within the earth Pollutants from coal are common; soot and sulfur problems Scrubbing Sulfur From Coal Coal Coal may be distilled for many products – coal gas, coal tar, coke, and ammonia – further distilled into benzene, toluene, naphthalene, phenol, and pitch – Coke is almost pure carbon; produces intense heat and little or no smoke, thus used in industrial processes