Chapter 10

1. Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chapter 10 An Introduction to Organic Chemistry: The Saturated Hydrocarbons Denniston Topping Caret 5th Edition

2. 10.1 The Chemistry of Carbon Why are there so many organic compounds? • Carbon forms stable, covalent bonds with other carbon atoms • Consider three allotropic forms of elemental carbon • Graphite in planar layers • Diamond is a three-dimensional network • Buckminsterfullerene is 60 C in a roughly spherical shape

3. Why are there so many organic compounds? 10.1 The Chemistry of Carbon Carbon atoms form stable bonds with other elements, such as: Oxygen Nitrogen Sulfur Halogen Presence of these other elements confers many new physical and chemical properties on an organic compound

4. Why are there so many organic compounds? 10.1 The Chemistry of Carbon Carbon atoms form double or triple bonds with: Other carbon atoms (double & triple) Oxygen (double only) Nitrogen (double & triple) These combinations act to produce a variety of organic molecules with very different properties

5. Why are there so many organic compounds? 10.1 The Chemistry of Carbon Carbon atoms can be arranged with these other atoms; is nearly limitless Branched chains Ring structures Linear chains Two organic compounds may even have the same number and kinds of atoms but completely different structures and thus, different properties These are called isomers

6. Many carbon compounds exist in the form of isomers Isomers are compounds with the same molecular formula but different structures An isomer example: both are C4H10 but have different structures Butane Methylpropane Isomers 10.1 The Chemistry of Carbon

7. Isomers All have the same molecular formula: C4H8 10.1 The Chemistry of Carbon

8. Important Differences Between Organic and Inorganic Compounds • Bond type • Organics have covalent bonds • Electron sharing • Inorganics usually have ionic bonds • Electron transfer • Structure • Organics • Molecules • Nonelectrolytes • Inorganics • Three-dimensional crystal structures • Often water-soluble, dissociating into ions -electrolytes 10.1 The Chemistry of Carbon

9. Important Differences Between Organic and Inorganic Compounds • Melting Point & Boiling Point • Organics have covalent bonds • Intermolecular forces broken fairly easily • Inorganics usually have ionic bonds • Ionic bonds require more energy to break • Water Solubility • Organics • Nonpolar, water insoluble • Inorganics • Water-soluble, readily dissociate 10.1 The Chemistry of Carbon

10. Comparison of Major Properties of Organic and Inorganic Compounds 10.1 The Chemistry of Carbon

11. Bonding Characteristics and Isomerism • One reason for the power of carbon is that it can form 4 covalent bonds • It appears to have only 2 available electrons • Carbon can hybridize its orbitals to move 2 electrons out of it 2s orbital 10.1 The Chemistry of Carbon

12. Hybrid Orbitals • Each carbon-hydrogen bond in methane arises from an overlap of a C(sp3) and an H(1s) orbital • 4 equivalent sp3 orbitals point toward the corners of a regular tetrahedron • The 4 sp3 hybrid orbitals of carbon combine with the 1s orbitals on 4 H to produce methane – CH4 10.1 The Chemistry of Carbon

13. Families of Organic Compounds • Hydrocarbons contain only carbon and hydrogen • They are nonpolar molecules • Not soluble in water • Are soluble in typical nonpolar organic solvents • Toluene • Pentane 10.1 The Chemistry of Carbon

14. Families of Organic Compounds • Hydrocarbons are constructed of chains or rings of carbon atoms with sufficient hydrogen atoms to fulfill carbon’s need for four bonds • Substituted hydrocarbon is one in which one or more hydrogen atoms is replaced by another atom or group of atoms 10.1 The Chemistry of Carbon

15. Division of the Family of Hydrocarbons 10.1 The Chemistry of Carbon

16. Hydrocarbon Saturation • Alkanes are compounds that contain only carbon-carbon and carbon-hydrogen single bonds • A saturated hydrocarbon has no double or triple bonds • Alkenes and alkynes are unsaturated because they contain at least one carbon to carbon double or triple bond 10.1 The Chemistry of Carbon

17. Cyclic Structure of Hydrocarbons • Some hydrocarbons are cyclic • Form a closed ring • Aromatic hydrocarbons contain a benzene ring or related structure 10.1 The Chemistry of Carbon

18. Common Functional Groups 10.1 The Chemistry of Carbon

19. 10.2 Alkanes • The general formula for a chain alkane is CnH2n+2 • In this formula n = the number of carbon atoms in the molecule • Alkanes are saturated hydrocarbons • Contain only carbon and hydrogen • Bonds are carbon-hydrogen and carbon-carbon single bonds

20. Formulas Used in Organic Chemistry • Molecular formula - lists kind and number of each type of atom in a molecule, no bonding pattern • Structural formula - shows each atom and bond in a molecule • Condensed formula - shows all the atoms in a molecule in sequential order indicating which atoms are bonded to which • Line formula - assume a carbon atom at any location where lines intersect • Assume a carbon at the end of any line • Each carbon in the structure is bonded to the correct number of hydrogen atoms 10.2 Alkanes

21. The Tetrahedral Carbon Atom 10.2 Alkanes • Lewis dot structure • The tetrahedral shape around the carbon atom • The tetrahedral carbon drawn with dashes and wedges • The stick drawing of the tetrahedral carbon atom • Ball and stick model of methane

22. Drawing Methane and Ethane 10.2 Alkanes Staggered form of ethane

23. Comparison of Ethane and Butane Structures 10.2 Alkanes

24. Names and Formulas of the First Ten Straight-Chain Alkanes 10.2 Alkanes

25. Butane Bp –0.4 oC Mp –139 oC Isobutane Bp –12 oC Mp –145 oC Structural Isomers • Constitutional/Structural Isomers differ in how atoms are connected • Two isomers of butane have different physical properties • The carbon atoms are connected in different patterns 10.2 Alkanes

26. Comparison of Physical Properties of Five Isomers of Hexane Compare the basic linear structure of hexane • All other isomers have one or more carbon atoms branching from the main chain • Branched-chain forms of the molecule have a much smaller surface area • Intermolecular forces are weaker • Boiling and melting points are lower than straight chains 10.2 Alkanes

27. Physical Properties of Organic Molecules • Nonpolar • Not water soluble • Soluble in nonpolar organic solvents • Low melting points • Low boiling points • Generally less dense (lighter) than water • As length (molecular weight) increases, melting and boiling points increase as does the density 10.2 Alkanes

28. Properties of Alkanes 10.2 Alkanes

29. Properties of Alkanes • Most of the alkanes are hydrophobic: water hating • Straight chain alkanes comprise a homologous series: compounds of the same functional class that differ by a –CH2- group • Nonpolar alkanes are: • Insoluble in water (a highly polar solvent) • Less dense than water and float on it 10.2 Alkanes

30. Alkyl Groups 10.2 Alkanes • An alkyl group is an alkane with one hydrogen atom removed • It is named by replacing the -ane of the alkane name with -yl • Methane becomes a methyl group

31. Alkyl Groups • All six hydrogens on ethane are equivalent • Removing one H generates the ethyl group • All 3 structures shown at right are the same 10.2 Alkanes

32. Names and Formulas of the First Five Alkyl Groups 10.2 Alkanes

33. Alkyl Group Classification • Alkyl groups are classified according to the number of carbons attached to the carbon atom that joins the alkyl group to a molecule • All continuous chain alkyl groups are 1º • Isopropyl and sec-butyl are 2º groups 10.2 Alkanes

34. Iso- Alkyl Groups • Propane: removal of a hydrogen generates two different propyl groups depending on whether an end or center H is removed 10.2 Alkanes n-propyl isopropyl

35. Sec- Alkyl Groups • n-butane gives two butyl groups depending on whether an end (1º) or interior (2º) H is removed 10.2 Alkanes n-butyl sec-butyl

36. Structures and Names of Some Branched-Chain Alkyl Groups 10.2 Alkanes

37. More Alkyl Group Classification • Isobutane gives two butyl groups depending on whether a 1o or 3o H is removed 10.2 Alkanes 1o C 3o C isobutyl t-butyl

38. Nomenclature • The IUPAC (International Union of Pure and Applied Chemistry) is responsible for chemical names • Before learning the IUPAC rules for naming alkanes, the names and structures of eight alkyl groups must be learned • These alkyl groups are historical names accepted by the IUPAC and integrated into modern nomenclature 10.2 Alkanes

39. Carbon Chain Length and Prefixes 10.2 Alkanes

40. IUPAC Names for Alkanes • The base or parent name for an alkane is determined by the longest chain of carbon atoms in the formula • The longest chain may bend and twist, it is seldom horizontal • Any carbon groups not part of the base chain are called branches or substituents • These carbon groups are also called alkyl groups 10.2 Alkanes

41. IUPAC Names for Alkanes • Rule 1 applied • Find the longest chain in each molecule • A=7 B=8 10.2 Alkanes

42. IUPAC Names for Alkanes • Number the carbon atoms in the chain starting from the end with the first branch • If both branches are equally from the ends, continue until a point of difference occurs 10.2 Alkanes

43. 1 6 7 8 2 4 5 3 2 1 3 4 5 6 this branch would be on C-4 if you started at correct C-8 7 IUPAC Names for Alkanes Number the carbon atoms correctly • Left: first branch is on carbon 3 • Right: first branch is on carbon 3 (From top) not carbon 4 (if number from right) 10.2 Alkanes

44. IUPAC Names for Alkanes • Write each of the branches/substituents in alphabetical order before the base/stem name (longest chain) • Halogens usually come first • Indicate the position of the branch on the main chain by prefixing its name with the carbon number to which it is attached • Separate numbers and letters with a hyphen • Separate two or more numbers with commas 10.2 Alkanes

45. IUPAC Names for Alkanes 10.2 Alkanes Name : 4-ethyl-2-methylhexane

46. IUPAC Names for Alkanes • Hyphenated and number prefixes are not considered when alphabetizing groups • Name the compound below • 5-sec-butyl-4-isopropylnonane 10.2 Alkanes

47. IUPAC Names for Alkanes • When a branch/substituent occurs more than once • Prefix the name with • di • tri • tetra • Then list the number of the carbon branch for that substituent to the name with a separate number for each occurrence • Separate numbers with commas • e.g., 3,4-dimethyl or 4,4,6-triethyl 10.2 Alkanes

48. IUPAC Names for Alkanes 10.2 Alkanes 5-ethyl-2,3-dimethylheptane ethyl>dimethyl

49. Practice: IUPAC Name 1 2 10.2 Alkanes 3 4 5 6 6-ethyl-6-isobutyl-3,3-dimethyldecane 7 8 9 10

50. 10.3 Cycloalkanes • Cycloalkanes have two less hydrogens than the corresponding chain alkane • Hexane=C6H14; cyclohexane=C6H12 • To name cycloalkanes, prefix cyclo- to the name of the corresponding alkane • Place substituents in alphabetical order before the base name as for alkanes • For multiple substituents, use the lowest possible set of numbers; a single substituent requires no number