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CH. 22 HYDROCARBON COMPOUNDS 22.1 HYDROCARBONS Organic Chemistry includes almost all carbon compounds Not limited to compounds found in living cells Hydrocarbon: organic compound made of only hydrogen and carbon atoms HYDROCARBONS Carbon atoms have 4 valence electrons Hydrogen atoms have 1 electron Carbon atoms will make 4 bonds Hydrogen atoms will only make one bond REPRESENTING HYDROCARBONS PROPERTIES OF HYDROCARBONS Nonpolar molecules Will not mix with water Mix with other nonpolar molecules Tend to be gas or liquid (with low BP) at room temperature Combustible in presence of oxygen and heat ALKANES Hydrocarbons with all single covalent bonds Can be straight chain or branched chain (or ring structure) Boiling Point and Melting Point increase with number of carbons in a straight chain compound NAMING STRAIGHT CHAIN ALKANES IUPAC: International Union of Pure and Applied Chemistry Name ends with suffix –ane Prefix indicates the number of carbon atoms Note: the prefixes for the first 4 carbons are different than the prefixes used for inorganic compounds! DRAWING STRUCTURAL FORMULAS Start with the number of carbon atoms, linked by single bonds Fill in as many hydrogen as necessary Condensed structural formulas can be used to save time and space PRACTICE Draw complete structural formulas for straight chain alkanes with a) Three carbon atoms b) Four carbon atoms c) Seven carbon atoms Name each of them. PRACTICE Draw the complete structural formula for a) Ethane b) Nonane c) Methane PRACTICE How many single bonds are there in a propane molecule? How many single bonds are there in a butane molecule? BRANCHED-CHAIN HYDROCARBONS One carbon atom is bonded to 3 or 4 other carbon atoms Branches are named as substituent groups The longest continuous carbon chain is the parent alkane (provides number of carbons for the name prefix) Hydrocarbon substituents are called alkyl groups Methyl Ethyl Propyl Butyl Pentyl, etc. PRACTICE Name this compound using the IUPAC system. *Notice that the longest chain is not written in a straight line. PRACTICE Name the following compounds. PRACTICE Draw the structural formula for 3-ethyl-2,4dimethylhexane. Draw the structural formula for 2,3dimethylbutane. Draw the structural formula for 3,4-diethyl-2,5dimethyloctane. 22.2 UNSATURATED HYDROCARBONS Saturated compound: contains the maximum number of hydrogen atoms per carbon atom (2n+2) Unsaturated compound: contains at least one double or triple bond ALKENES Alkene: a hydrocarbon with at least one double bond Naming Find the longest continuous carbon chain that contains the double bond (this is the parent alkene) Name the parent alkene by the number prefix and end in –ene Number the parent chain so that the double bond has the lowest possible number Any substituents are named the same as with alkanes ALKYNES Alkyne: a hydrocarbon with at least one triple bond Naming Number the parent chain so that the triple bond has the lowest possible number on the longest continuous chain Name the parent chain with the number prefix End the name in –yne Name substituents as with alkanes PRACTICE Draw a complete structural formula for each of the following hydrocarbon compounds. Ethane Ethene Ethyne Propane Propene Propyne 22.3 ISOMERS Isomers have the same molecular formula but different structures Constitutional (structural) isomers: same molecular formula but the atoms are arranged differently Physical properties (BP, MP) differ Chemical reactivities differ STEREOISOMERS Stereoisomers: atoms are joined in same order, but in different arrangements in space Cis-trans isomers Enantiomers CIS-TRANS ISOMERS Cis-trans isomers are most commonly found in compounds with double bonds (alkenes) Cis configuration: similar groups are on the same side of the double bond Trans configuration: similar groups are on opposite sides of the double bond ENANTIOMERS Occurs when a central atom (C) has four different atoms or groups attached When this central atom is carbon, it is called an asymmetric carbon Groups attached to an asymmetric carbon can form mirror images of each other When these mirror images are not superimposable, the two forms are called enantiomers The enantiomers have identical physical properties but can have different chemical reactions PRACTICE 22.4 HYDROCARBON RINGS Cyclic Hydrocarbons AROMATIC HYDROCARBONS Aromatic compounds contain a benzene ring Non-aromatic compounds are called aliphatic Benzene Resonance increases stability Two forms are extremes, the true bonding is an average SUBSTITUTED AROMATIC COMPOUNDS A compound with substituents added to benzene ring use benzene as the parent hydrocarbon When the benzene ring is a substituent, it is called a phenyl group SUBSTITUTED AROMATIC COMPOUNDS With 2 substituent groups on a benzene ring numbering becomes part of the name The different constitutional isomers have different properties 22.5 HYDROCARBONS FROM EARTH’S CRUST Natural Gas Source of low-mass alkanes 80% methane, 10% ethane, 4% propane, 2% butane 4% contains nitrogen, higher mass hydrocarbons, and helium Combustion requires O2 gas Methane burns with a hot, clean flame 22.5 HYDROCARBONS FROM EARTH’S CRUST Petroleum More complex compounds than in natural gas Mostly straight or branched-chain alkanes Includes some aromatic compounds and sulfur-, oxygen-, or nitrogen-containing compounds Petroleum refining begins with distilling crude oil into fractions by boiling point Cracking breaks down larger hydrocarbons into smaller, more useful hydrocarbons BIOREMEDIATION Using oil-eating microbes (mostly bacteria) to clean up an oil-spill Microbes digest crude oil into mostly CO2 and H2O Takes time to work Most effective along shorelines after other means of cleaning 22.5 HYDROCARBONS FROM EARTH’S CRUST Coal Classified by hardness and carbon content Mostly condensed aromatic hydrocarbons with high mass Leaves more soot when burned Forms in multiple stages from pressure and heat over time Peat lignite bituminous anthracite
