Chapter_2_notes

Chapter_2_notes - Chem 2261 Notes Nomenclature, Physical...

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Chem 2261 Notes Nomenclature, Physical Properties, and Conformation (Bruice, Chapter 2) 1 Alkane Isomers Alkanes (see table 2.1, p. 72) Alkanes are hydrocarbons containing single bonds only. Alkanes have the general formula C n H 2n+2 where n = any integer. Constitutional Isomers: Compounds with the same molecular formula which differ in the connectivity of their atoms. Examples: 1. C 4 H 10 isomers and structural representations H 3 C H 2 C C H 2 CH 3 Condensed Structure Skeletal Structure butane H 3 C CH CH 3 isobutane CH 3 H 3 C-CH 2 -CH 2 -CH 3 H 3 C-CH-CH 3 CH 3 2. C 5 H 12 isomers, pentane, isopentane, and neopentane n -pentane isopentane neopentane Number of constitutional isomers increases rapidly as alkane chain gets longer. Number of isomers of C n H 2n+2 n number of isomers 4 2 butanes 5 3 pentanes 65 h e x a n e s 7 9 heptanes 8 18 octanes 9 35 nonanes 10 75 decanes 11 159 undecanes 12 355 dodecanes 13 802 tridecanes 20 366,319 eicosanes
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Chem 2261 Notes Nomenclature, Physical Properties, and Conformation (Bruice, Chapter 2) 2 Can you write the structural formulas for the five isomeric C 6 H 14 hexane and nine isomeric C 7 H 16 heptane isomers? C 6 H 14 5 isomers 12 3 4 5 C 7 H 16 9 isomers 3 4 5 6 789 see also Problems 2-4, 8, 10, 49, 52, 60
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Chem 2261 Notes Nomenclature, Physical Properties, and Conformation (Bruice, Chapter 2) 3 Nomenclature of Alkyl Substituents Removal of one H from an alkane = an alkyl (or R) group. Examples (see table 2.2, p. 77) methyl ethyl propyl isopropyl butyl isobutyl sec -butyl tert -butyl H 3 CCH 2 CH 2 CH 2 H 3 CH 3 H 3 2 CH 2 H 3 2 H 3 C H 3 CH 2 H 3 CC CH 3 H 3 2 CH CH 3 CH 3 CH 3 Combination of R-groups with heteroatoms: Replacement of H by OH, NH 2 or X (halogen, F, Cl, Br, or I) results in an alcohol, amine and alkyl halide, respectively. Examples NH 2 = ethyl amine = isopropyl alcohol = sec -butyl bromide Br H 3 2 NH 2 H 3 OH CH 3 H 3 2 CH Br CH 3 OH
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Chem 2261 Notes Nomenclature, Physical Properties, and Conformation (Bruice, Chapter 2) 4 Nomenclature of Alkyl Halides The common names of alkyl halides are obtained by citing the name of the alkyl group followed by the name of the halide corresponding to the halogen (i.e., fluoride for F, chloride for Cl, etc.). In the IUPAC system, alkyl halides are named as substituted alkanes (haloalkanes as opposed to alkyl halides) using the halo prefix corresponding to the halogen substituent (i.e., fluoro for F, chloro for Cl, etc.). For simple, relatively unsubstituted alkyl chains you may see either naming convention. common name IUPAC name ethyl chloride chloroethane propyl fluoride 1-fluoropropane isopropyl iodide 2-iodopropane sec -butyl bromide 2-bromobutane H 3 CCH CH 2 CH 3 Br H 3 CH 3 I H 3 2 CH 2 F H 3 2 Cl For alkyl halides with more complex (e.g., highly branched) alkyl chains or possessing several halogen substituents, the IUPAC naming system is more common and preferable. The IUPAC system is discussed in the next section on nomenclature of substituted alkanes.
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This note was uploaded on 04/21/2008 for the course CHEM 2261 taught by Professor Crowe during the Fall '08 term at LSU.

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Chapter_2_notes - Chem 2261 Notes Nomenclature, Physical...

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