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Alkanes

Alkanes. Hydrocarbons. Aliphatic. Aromatic. Hydrocarbons. Aliphatic. Aromatic. Alkanes. Alkenes. Alkynes. H. H. H. H. C. C. H. H. Hydrocarbons. Alkanes are hydrocarbons in which all of the bonds are single bonds. Aliphatic. Alkanes. H. H. C. C. H. H. Hydrocarbons.

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Alkanes

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  1. Alkanes

  2. Hydrocarbons Aliphatic Aromatic

  3. Hydrocarbons Aliphatic Aromatic Alkanes Alkenes Alkynes

  4. H H H H C C H H Hydrocarbons • Alkanes are hydrocarbons in which all of the bonds are single bonds. Aliphatic Alkanes

  5. H H C C H H Hydrocarbons • Alkenes are hydrocarbons that contain a carbon-carbon double bond. Aliphatic Alkenes

  6. HC CH Hydrocarbons • Alkynes are hydrocarbons that contain a carbon-carbon triple bond. Aliphatic Alkynes

  7. H H H H H H Hydrocarbons • The most common aromatic hydrocarbons are those that contain a benzene ring. Aromatic

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

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

  10. Structure of Methane • tetrahedral • bond angles = 109.5° • bond distances = 110 pm • but structure seems inconsistent withelectron configuration of carbon

  11. Structure of Ethane • tetrahedral geometry at each carbon • C—H bond distance = 110 pm • C—C bond distance = 153 pm C2H6 CH3CH3

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

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

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

  15. Nomenclature of Alkanes • Rules for naming compounds are given by the International Union for Pure and Applied Chemistry (IUPAC). • To name alkanes: • Find the longest chain and use it as the name of the compound. • Number the carbon atoms starting with the end closest to the substituent. • Name and give the location of each substituent. • When two or more substituents are present list them in alphabetical order.

  16. 1. Determine the number of carbons in the parent hydrocarbon 2. Number the chain so that the substituent gets the lowest possible number Nomenclature of Alkanes

  17. 3. Number the substituents to yield the lowest possible number in the number of the compound (substituents are listed in alphabetical order) 4. Assign the lowest possible numbers to all of the substituents

  18. 5. When both directions lead to the same lowest number for one of the substituents, the direction is chosen that gives the lowest possible number to one of the remaining substituents 6. If the same number is obtained in both directions, the first group receives the lowest number

  19. 7. In the case of two hydrocarbon chains with the same number of carbons, choose the one with the most substituents 8. Certain common nomenclatures are used in the IUPAC system

  20. Nomenclature of Alkanes

  21. Types of Carbons • primary (1o) - bonded to only 1 other carbon • secondary (2o) - bonded to 2 other carbons • tertiary (3o) - bonded to 3 other carbons • quaternary (4o) - bonded to 4 other carbons

  22. Conformations are different spatial arrangements of a molecule that are generated by rotation about single bonds.

  23. Ethane Eclipsed conformation

  24. Ethane Staggered conformation

  25. H H H H H H H H H H H H Projection formulas of the staggeredconformation of ethane Newman Sawhorse

  26. H H H H H H H H H H H H Anti relationships 180° Two bonds are anti when the angle between them is 180°.

  27. Gauche relationships H 60° H H H H H H H H H H H Two bonds are gauche when the angle between them is 60°.

  28. An important point: The terms anti and gauche applyonly to bonds (or groups) on adjacentcarbons, and only to staggeredconformations.

  29. 12 kJ/mol 0° 60° 120° 180° 240° 300° 360°

  30. Conformational Analysis of Butane: C2-C3 Rotation

  31. The most stable conformation of unbranchedalkanes has anti relationships between carbons Hexane

  32. Reactions with Alkanes • The C-C and C-H bonds are very strong. Therefore, alkanes are very unreactive. • At room temperature alkanes do not react with acids, bases, or strong oxidizing agents. • Alkanes do combust in air (making them good fuels): 2C2H6(g) + 7O2(g)  4CO2(g) + 6H2O(l) H = -2855 kJ

  33. Alkanes are very unreactive compounds becausethey have only strong s bonds and atoms with no partial charges However, alkanes do react with Cl2 and Br2

  34. Reaction of Alkane with Cl2 or Br2

  35. Petroleum is a complex mixture of alkanes and cycloalkanes that can be separated by distillation

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