Organic Chemistry (C4H10) Organic Chemistry and Hydrocarbons “Organic” originally referred to any chemicals that came from organisms 1828 - German chemist Friedrich Wohler synthesized urea in a lab Today, organic chemistry is the chemistry of virtually all compounds containing the element carbon Friedrich Wohler 1800 – 1882 Used inorganic substances to synthesize urea, a carbon compound found in urine. This re-defined organic chemistry. 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. These are the Hydrocarbons Organic Chemistry and Hydrocarbons Hydrocarbons contain only two elements: hydrogen, carbon Homologous series of hydrocarbons: Saturated hydrocarbons – Alkanes • Only single bonds between carbons • Name ends in ___ane • General formula CnH2n+2 • Methane CH4 Ethane C2H6 Unsaturated hydrocarbons – Contain at least one double or triple bond – Alkenes • Contain one double bond • Name ends in ___ene • General formula CnH2n – Alkynes • Contain one triple bond • Name ends in ___yne • General formula CnH2n-2 Saturated hydrocarbons – (alkanes) single carbon-carbon bonds. Unsaturated hydrocarbons at least one multiple carbon-carbon bond. (alkenes and alkynes) Organic Chemistry and Hydrocarbons Regents Reference Tables P,Q and R Carbon has 4 valence electrons, thus forms 4 covalent bonds – not only with other elements, but also forms bonds WITH ITSELF (nonpolar) Table P gives the prefix used to name the first 10 hydrocarbons in an homologous series. Table Q gives the general formula and examples (name and structure) of the homologous series of hydrocarbons. Straight-Chain Alkanes Straight-chain alkanes contain any number of carbon atoms, one after the other, in a chain pattern meaning one linked to the next (not always straight- can bend) C-C-C C-C-C-C etc. Names of alkanes always will always end with –ane Ratio is CN H2N + 2 Straight-Chain Alkanes Combined with the -ane ending is a prefix for the number of carbons Homologous series- a group of compounds that have a constant increment of change In alkanes, it is: -CH2- (methylene) Straight-Chain Alkanes alkanes used for fuels: methane, propane, butane, octane As the number of carbons increases, so does the boiling and melting pt. Many – The first 4 are gases; #5-15 are liquids; higher alkanes are solids Condensed structural formulas? Naming Straight-Chain Alkanes Names recommended by IUPAC - the International Union of Pure and Applied Chemistry end with –ane; the root part of the name indicates the # of carbons We sometimes still rely on common names, some of which are well-known Naming Straight-Chain Alkanes IUPAC names may be long and cumbersome Common names may be easier or more familiar, but usually do not describe the chemical structure! –Methane is natural gas or swamp gas The prefix of the name tells you how many carbons in the chain.The suffix tells you the type of hydrocarbon. Branched-Chain Alkanes Branched-chain means that other elements besides hydrogen may be attached to the carbon –halogens, oxygen, nitrogen, sulfur, and even other carbons –any atom that takes the place of a hydrogen on a parent hydrocarbon is called a substituent, or the branched part Branched-Chain Alkanes A hydrocarbon substituent is called an alkyl group or sometimes radicals –use the same prefixes to indicate the number of carbons, but -ane ending is now -yl such as: methyl, ethyl, propyl, etc. Gives much more variety to the organic compounds Branched-Chain Alkanes Rules 1. for naming Longest C-C chain is parent 2. Number so branches have lowest # 3. Give position number to branch 4. Prefix (di, tri) more than one branch 5. Alphabetize branches (not prefix) 6. Use proper punctuation ( - and , ) Branched-Chain Alkanes From the name, draw the structure, in a right-to-left manner: 1. Find the parent, with the -ane 2. Number carbons on parent 3. Identify substituent groups (give lowest number); attach 4. Add remaining hydrogens - Page 700 Alkanes Draw 3-ethylpentane Draw 2,3,4-trimethylhexane Since the electrons are shared equally, the molecule is nonpolar –thus, not attracted to water –oil (a hydrocarbon) not soluble in H2O –“like dissolves like” Alkenes Multiple bonds can also exist between the carbon atoms Hydrocarbons containing carbon to carbon double bonds are called alkenes (CnH2n) C=C C-C=C Called “unsaturated” if they contain double or triple bonds Naming Alkenes Find longest parent that has the double bond in it New ending: -ene Number the chain, so that the double bond gets the lower number Name and number the substituents Alkynes Hydrocarbons containing carbon to carbon triple bonds are called alkynes ethyne (CnH2n-2) -C C Alkynes are not plentiful in nature Simplest is ethyne- common name acetylene (fuel for torches) Table 22.3, p. 703 for boiling pt. Isomers Compounds that have the same molecular formula, but different molecular structures, are called structural isomers Structural Isomers Butane and 2-methylpropane (made by breaking carbon off the end, and making it a branch in the middle) Also have different properties, such as b.p., m.p., and reactivity Structural Isomers of Butane, C4H10 Stereoisomers Don’t forget that these structures are really 3-dimensional stereoisomers- molecules of the same molecular structure that differ only in the arrangement of the atoms in space. Two types are a) geometric and b) optical Geometric Isomers There is a lack of rotation around a carbon to carbon multiple bond – has an important structural implication – Two possible arrangements: 1. trans configuration - substituted groups on opposite sides of double bond 2. cis configuration - same side Geometric Isomers Trans-2-butene Substituted groups are on the same side of the double bond (in this case, both are above) Substituted groups are on opposite sides of the double bond (in this case, one is above, the other is below) Cis-2-butene Geometric Isomers Trans-2-butene and Cis-2-butene differ in the geometry of the substituted groups (to double bond) like other structural isomers, have different physical and chemical properties Optical Isomers Asymmetric carbon? C with 4 different groups attached. Molecules containing asymmetric carbons have “handedness”, and exist as stereoisomers. Optical Isomers, and these will each show an asymetric carbon (4 different branches attached) The asymetric carbon Hydrocarbon Rings Cyclic Hydrocarbons The two ends of the carbon chain are attached in a ring in a cyclic hydrocarbon – named as “cyclo- ____” hydrocarbon compounds that do NOT contain rings are known as aliphatic compounds Aromatic Hydrocarbons A special group of unsaturated cyclic hydrocarbons is known as arenes – contain single rings, or groups of rings – also called “aromatic hydrocarbons”, because of pleasant odor – simplest aromatic is benzene (C6H6) – Term “aromatic” applies to materials with bonding like that of benzene Aromatic Hydrocarbons Benzene is a six-carbon ring, with alternating double and single bonds – exhibits resonance, due to location of the double and single bonds-Benzene derivatives possible: – methylbenzene, 3-phenylhexane, ethylbenzene Aromatic Hydrocarbons One derivative of Benzene is called phenylethene, or commonly named STYRENE. Foamed styrene is trademarked by Dow Chemical as CH2 “styrofoam” CH Other manufacturers items usually just called “foam cups” Aromatic Hydrocarbons Benzene derivatives can have two C or more substitutents: – 1,2-dimethylbenzene – 1,3-dimethylbenzene – 1,4-dimethylbenzene C C Can C use ortho for 1,2; meta for 1,3; and para for 1,4 Hydrocarbons From Earth’s Crust Natural Gas Fossil fuels provide much of the world’s energy Natural gas and petroleum contain mostly the aliphatic (or straight-chain) hydrocarbons – formed from marine life buried in sediment of the oceans 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, and is one of it’s major sources 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 Incomplete 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 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 – starts materials for plastics and paints Coal From huge fern trees and mosses decaying millions of years ago under great pressure of rocks / soil. 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 BIG BRUTUS Dragline used to remove the overburden of a strip mining coal field near West Mineral, Kansas. Note the size of the man standing next to it. Coal Coal may be distilled for many products – coal gas, coal tar, coke, and ammonia – further distilled into benzene, toluene, naphthalene, phenol- the aromatics – Coke is almost pure carbon; produces intense heat and little or no smoke, thus used in industrial processes