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Introduction to Alkanes: Methane, Ethane, and Propane

Introduction to Alkanes: Methane, Ethane, and Propane. C n H 2 n +2. The Simplest Alkanes. Methane (CH 4 ) CH 4 Ethane (C 2 H 6 ) CH 3 CH 3 Propane (C 3 H 8 ) CH 3 CH 2 CH 3. bp -160°C. bp -89°C. bp -42°C. Isomeric Alkanes: The Butanes. C 4 H 10. n -Butane CH 3 CH 2 CH 2 CH 3

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Introduction to Alkanes: Methane, Ethane, and Propane

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  1. Introduction to Alkanes:Methane, Ethane, and Propane CnH2n+2

  2. The Simplest Alkanes • Methane (CH4) CH4 • Ethane (C2H6) CH3CH3 • Propane (C3H8) CH3CH2CH3 bp -160°C bp -89°C bp -42°C

  3. Isomeric Alkanes: The Butanes C4H10

  4. n-Butane CH3CH2CH2CH3 • Isobutane (CH3)3CH bp -0.4°C bp -10.2°C

  5. Higher n-Alkanes

  6. CH3CH2CH2CH2CH3 n-Pentane CH3CH2CH2CH2CH2CH3 n-Hexane CH3CH2CH2CH2CH2CH2CH3 n-Heptane

  7. The C5H12 Isomers

  8. C5H12 (CH3)2CHCH2CH3 CH3CH2CH2CH2CH3 Isopentane n-Pentane (CH3)4C Neopentane

  9. How many isomers? The number of isomeric alkanes increases as the number of carbons increase. There is no simple way to predict how many isomers there are for a particular molecular formula.

  10. Number of Constitutionally Isomeric Alkanes • CH4 1 • C2H6 1 • C3H8 1 • C4H10 2 • C5H12 3 • C6H14 5 • C7H16 9 • C8H18 18 • C9H20 35 • C10H22 75 • C15H32 4,347 • C20H42 366,319 • C40H82 62,491,178,805,831

  11. Systematic Nomenclature • International Union of Pure and Applied Chemistry • IUPAC • Committee on Organic Nomenclature

  12. The alkanes

  13. Nomenclature of the Alkanes • Alkanes always have the ending -ane. • Side chains (substituents) are named as alkyl groups.

  14. Common alkyl groups (C1 through C4)

  15. IUPAC nomenclature of alkanes • identify the longest chain -- parent • number from the end closest to first branch • Name the groups attached to the chain, using the carbon number as the locator. • Alphabetize substituents. • Use di-, tri-, etc., for multiples of same substituent • combine number and name of substituent with parent name, separating with hyphen

  16. => Longest Chain • The number of carbons in the longest chain determines the base name: ethane, hexane. • If there are two possible chains with the same number of carbons, use the chain with the most substituents.

  17. 1 3 4 5 2 6 7 Number the Carbons • Start at the end closest to the first attached group. • If two substituents are equidistant, look for the next closest group.

  18. Organic nomenclature 4 3 2 1 2-methylbutane

  19. Find the longest continuouscarbon chain 1 2 3 4 5 3-methylpentane

  20. You must choose the longestcontinuous carbon chain 4 3 2 1 5 6 7 4-ethylheptane

  21. IUPAC rules 1. Find the longest straight chain = parent chain 2. Number the parent chain in the direction that gives the lowest number to the substituents at the first point of difference. 3. Two or more identical groups are indicated by di, tri, tetra, etc. Longest chain is 7 (not 6). This is 3-methylheptane. . 2,3,6-trimethylheptane (not 2,5,6-trimethyl heptane) 2,2,6,6,7-pentamethyloctane (not 2,3,3,7,7-pentamethyloctane)

  22. IUPAC rules 4. Different groups are listed in alphabetical order (di, tri, tetra, etc. don’t count; n, sec, tert don’t count; iso does). 5. If the numbering is the same in both directions, choose the numbering to follow the alphabetical order. 6-ethyl-5-isopropyl-2,2-dimethyloctane 5-ethyl-6-methyldecane

  23. IUPAC rules 6. When two or more chains compete for the longest, the choice goes to the one with the greater number of side groups. 2,4,6-trimethyl-5-propyloctane

  24. Number from the end nearestthe first substituent 7 6 5 4 3 2 1 4-ethyl-3-methylheptane

  25. Number from the end nearestthe first substituent 8 7 6 5 4 3 2 1 3-ethyl-5-methyloctane

  26. Use “di-” with two substituents 1 2 3 4 2,3-dimethylbutane

  27. Every substituent must get a number 1 2 3 4 5 6 3,3-dimethylhexane

  28. Number from the end nearestfirst substituent 10 9 8 7 6 5 4 3 2 1 2,7,8-trimethyldecane

  29. Number from the end which hasthe “first difference” 1 2 3 4 5 6 7 8 9 10 3,4,8-trimethyldecane

  30. A More-Highly-SubstitutedCarbon Takes Precedence 5 4 3 2 1 2,2,4-Trimethylpentane

  31. Which end do we number from? 8 7 6 5 4 3 2 1 3-ethyl-6-methyloctane

  32. IUPAC rules Name the following compounds. 6-ethyl-2,2,5,7-tetramethylnonane (not 6,7-diethyl-2,2,5-trimethyloctane. 7-tert-butyl-8-isobutyl-4-isopropyldodecane (hyphenated words aren’t alphabetized). OR 7-(1,1-dimethylethyl)-4-(1-methylethyl)- 8-(2-methylpropyl)dodecane

  33. Good Luck! 7-(1,1-Dimethylbutyl)-3-ethyl-7-methyldodecane

  34. Branched Substituents isopropyl sec-butyl isobutyl tert-butyl (t-butyl) neo-pentyl

  35. Halogens and other side groups • Fluoro –F • Chloro –Cl • Bromo –Br • Iodo –I • Nitro –NO2

  36. Bromoethane “Ethyl bromide”

  37. 2-Chloro-2-methylpropane “tert-Butyl chloride”

  38. 2-Bromo-3-methylpentane

  39. 1 2 3 Complex Substituents • If the branch has a branch, number the carbons from the point of attachment. • Name the branch off the branch using a locator number. • Parentheses are used around the complex branch name. 1-methyl-3-(1,2-dimethylpropyl)cyclohexane =>

  40. The isopropyl group can be named as a “complex” substituent 1-methylethyl

  41. If you can name this,you can name almost anything! 1 2 3 4 5 6 7 8 9 4-isopropyl-2,6,6-trimethylnonane

  42. Now, rename the isopropyl group. Notice the alphabetical order! 1 2 3 4 5 6 7 8 9 2,6,6-trimethyl-4-(1-methylethyl)nonane

  43. Naming complex substituents -- this one is alphabetized under d 1,3-dimethylbutyl

  44. deciding on alphabetical order for complex groups • Complex groups are alphabetized under the first letter of the name • (1,3-dimethylbutyl) = d • (1,1,2-trimethylpropyl) = t • (1-ethyl-1,2-dimethylbutyl) = e

  45. Naming complex substituents 2-ethyl-1,1-dimethylbutyl

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