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Lecture Organic chemistry: Chapter 3 - L. G. Wade, Jr.

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Chapter 3 - Structure and stereochemistry of alkanes. In this chapter you will learn: Draw and name the isomers of alkanes, and explain the trends in their physical properties; draw alkane conformations, compare their energies, and predict the most stable conformations; draw and name the isomers of cycloalkanes, and explain ring strain; draw the conformations of cycloalkanes, compare their energies, and predict the most stable conformations. | Chapter 3 Organic Chemistry, 7th Edition L. G. Wade, Jr. ã 2010, Prentice Hall Structure and Stereochemistry of Alkanes Hydrocarbons are molecules that are made of carbon and hydrogen ONLY. Hydrocarbons Alkanes General formula: CnH2n+2 Found in everything from natural gas to petroleum. The smaller alkanes have very low boiling points (b.p.) therefore they are gases. CH4 C2H6 C3H8 b.p. -160oC -89oC -42oC Alkane Examples Small Alkanes (CnH2n+2) Methane Ethane Propane Butane: C4H10 Constitutional isomers are compounds with the same molecular formula but the carbons are connected differently. C H 3 C H 2 C H 2 C H 3 n - b u t a n e C H 3 C H C H 3 i s o - b u t a n e C H 3 Pentanes: C5H12 n-pentane iso-pentane neo-pentane C H 3 C H 2 C H 2 C H 2 C H 3 C H 3 C H C H 2 C H 3 C H 3 C C H 3 C H 3 C H 3 C H 3 IUPAC International Union of Pure and Applied Chemistry Common names kept: methane, ethane, propane, butane. Alkanes: suffix “-ane” will be used after the | Chapter 3 Organic Chemistry, 7th Edition L. G. Wade, Jr. ã 2010, Prentice Hall Structure and Stereochemistry of Alkanes Hydrocarbons are molecules that are made of carbon and hydrogen ONLY. Hydrocarbons Alkanes General formula: CnH2n+2 Found in everything from natural gas to petroleum. The smaller alkanes have very low boiling points (b.p.) therefore they are gases. CH4 C2H6 C3H8 b.p. -160oC -89oC -42oC Alkane Examples Small Alkanes (CnH2n+2) Methane Ethane Propane Butane: C4H10 Constitutional isomers are compounds with the same molecular formula but the carbons are connected differently. C H 3 C H 2 C H 2 C H 3 n - b u t a n e C H 3 C H C H 3 i s o - b u t a n e C H 3 Pentanes: C5H12 n-pentane iso-pentane neo-pentane C H 3 C H 2 C H 2 C H 2 C H 3 C H 3 C H C H 2 C H 3 C H 3 C C H 3 C H 3 C H 3 C H 3 IUPAC International Union of Pure and Applied Chemistry Common names kept: methane, ethane, propane, butane. Alkanes: suffix “-ane” will be used after the number of carbons. Example: An alkane with 5 carbons is “penta” for five and the suffix “-ane”: pentane IUPAC Rules Rule 1: Find the longest continuous chain of carbon atoms, and use the name of this chain as the base name of the compound. Rule 2: Number the longest chain, beginning with the end of the chain nearest a substituent. Rule 3: Name the groups attached to the longest chain as alkyl groups. Give the location of each alkyl group by the number of the main chain carbon atom to which it is attached. Write the alkyl groups in alphabetical order regardless of their position on the chain. Rule 1: Find the Longest Chain of Consecutive Carbons. The longest chain is six carbons: hexane Main Chain When there are two longest chains of equal length, use the chain with the greatest number of substituents. Figure: 03_01-04UN.jpg Title: Nomenclature: Same Length Chains Caption: When looking for the longest continuous chain, look to find all the different chains of that .