Chapter 22 “Hydrocarbon Compounds”

1. Chapter 22“Hydrocarbon Compounds” Mr. Gower Troy High School (C4H10)

2. Organic Chemistry and Hydrocarbons • “Organic” originally referred to any chemicals that came from organisms • 1828 - German chemist Friedrich Wohler synthesized urea in a lab • Today, organic chemistry is the chemistry of virtually all compounds containing the element carbon

3. Friedrich Wohler • 1800 – 1882 • Used inorganic substances to synthesize urea, a carbon compound found in urine. • This re-defined organic chemistry.

4. Organic Chemistry and Hydrocarbons • Over a million organic compounds, with a dazzling array of properties • Why so many? Carbon’s unique bonding ability! • Let’s start with the simplest of the organic compounds. These are the Hydrocarbons.

5. Organic Chemistry and Hydrocarbons • Hydrocarbons contain only two elements: 1) hydrogen, and 2) carbon • simplest hydrocarbons called “alkanes”, which contain only carbon to carbon singlecovalent bonds (CnH2n+2) • methane (CH4) with one carbon is the simplest alkane. It is the major component of natural gas.

6. Organic Chemistry and Hydrocarbons • Review structural formulas - p.694 • Carbon has 4 valence electrons, thus forms 4 covalent bonds • not only with other elements, but also forms bonds WITH ITSELF (nonpolar) • Ethane (C2H6) is the simplest alkane with a carbon to carbon bond

7. Organic Chemistry and Hydrocarbons One carbon atom can form a single covalent bond with four hydrogen atoms.

8. Organic Chemistry and Hydrocarbons Formulas and Models for Methane and Ethane Ball-and-stick model Space-filling model

9. Straight-Chain Alkanes • Straight-chain alkanes contain any number of carbon atoms, one after the other, in a chain pattern - meaning one linked to the next (not always straight) C-C-C C-C-C-C etc. • Names of alkanes always will always end with -ane

10. Alkanes Straight-Chain Alkanes Ethane is the simplest of the straight-chain alkanes, which contain any number of carbon atoms, one after the other, in a chain.

11. Straight-Chain Alkanes • Combined with the -ane ending is a prefix for the number of carbons -Table 22.1, page 695 • Homologous series- a group of compounds that have a constant increment of change • In alkanes, it is: -CH2- (methylene)

12. Alkanes A group of compounds forms a homologous series if there is a constant increment of change in molecular structure from one compound in the series to the next.

13. Alkane MP and BP- Van der Waals Forces.

14. Straight-Chain Alkanes • Many alkanes used for fuels: methane, propane, butane, octane • As the number of carbons increases, so does the boiling and melting pt. • The first 4 are gases; #5-15 are liquids; higher alkanes are solids • Condensed structural formulas? Note examples on page 696

15. Alkanes

16. Naming Straight-Chain Alkanes • Names recommended by IUPAC - the International Union of Pure and Applied Chemistry • end with –ane; the root part of the name indicates the # of carbons • We sometimes still rely on common names, some of which are well-known

17. Naming Straight-Chain Alkanes • IUPAC names may be long and cumbersome • Common names may be easier or more familiar, but usually do not describe the chemical structure! • Methane is natural gas or swamp gas

18. Branched-Chain Alkanes • Branched-chain means that other elements besides hydrogen may be attached to the carbon • halogens, oxygen, nitrogen, sulfur, and even other carbons • any atom that takes the place of a hydrogen on a parent hydrocarbon is called a substituent, or the branchedpart

19. Alkanes Branched-Chain Alkanes An atom or group of atoms that can take the place of a hydrogen atom on a parent hydrocarbon molecule is called a substituent.

20. Branched-Chain Alkanes • A hydrocarbon substituent is called an alkyl group or sometimes radicals • use the same prefixes to indicate the number of carbons, but -ane ending is now -yl such as: methyl, ethyl, propyl, etc. • Gives much more variety to the organic compounds

21. Branched-Chain Alkanes • Rules for naming – (go from right to left) - page 698 1. Longest C-C chain is parent 2. Number so branches have lowest # 3. Give position number to branch 4. Prefix (di, tri) more than one branch 5. Alphabetize branches (not prefix) 6. Use proper punctuation ( - and , )

22. - Page 699

23. Branched-Chain Alkanes • From the name, draw the structure, in a right-to-left manner: 1. Find the parent, with the -ane 2. Number carbons on parent 3. Identify substituent groups (give lowest number); attach 4. Add remaining hydrogens

24. - Page 700

25. Alkanes A hydrocarbon substituent is called an alkyl group. An alkane with one or more alkyl groups is called a branched-chain alkane.

26. Practice- page 699

27. Alkanes • Draw 3-ethylpentane • Draw 2,3,4-trimethylhexane • Since the electrons are shared equally, the molecule is nonpolar • thus, not attracted to water • oil (a hydrocarbon) not soluble in H2O • “like dissolves like”

28. 22.1 Section Quiz. 1. Choose the correct words for the spaces. Because carbon has ______ valence electrons, it can form ______________ bonds. a. four, four covalent b. four, four ionic c. six, six covalent d. six, four or fewer covalent

29. 22.1 Section Quiz. 2. Alkanes are hydrocarbons that contain only ___________ bonds. a. carbon-carbon b. single covalent c. carbon-hydrogen d. ionic

30. 22.1 Section Quiz 3. Choose the correct words for the spaces. Hydrocarbons are highly soluble in _______ solvents because they are ________ molecules. a. nonpolar, nonpolar b. nonpolar, polar c. polar, nonpolar d. polar, polar

31. Alkenes • Multiple bonds can also exist between the carbon atoms • Hydrocarbons containing carbon to carbon double bonds are called alkenes(CnH2n) C=C C-C=C • Called “unsaturated” if they contain double or triple bonds

32. Naming Alkenes • Find longest parent that has the double bond in it • New ending: -ene • Number the chain, so that the double bond gets the lower number • Name and number the substituents • Samples on page 702

33. Alkenes Alkenes are hydrocarbons that contain one or more carbon-carbon double covalent bonds.

34. Alkenes Because rotation is restricted around the double bond, atoms in ethene lie in one plane. Ethene

35. Alkynes • Hydrocarbons containing carbon to carbon triple bonds are called alkynes (CnH2n-2) -C C- • Alkynes are not plentiful in nature • Simplest is ethyne- common name acetylene (fuel for torches) • Table 22.3, p. 703 for boiling pt. ethyne

36. Alkynes At least one carbon-carbon bond in an alkyne is a triple covalent bond. Other bonds may be single or double carbon-carbon bonds and single carbon-hydrogen bonds.

37. Alkynes Straight-chain and branched-chain alkanes, alkenes, and alkynes are aliphatic hydrocarbons. • Alkenes and alkynes are unsaturated!

38. Alkenes

39. Alkynes The triple bond restricts rotation in an ethyne molecule, which has a linear shape.

40. 22.2 Section Quiz. 1. Alkenes and alkynes are called unsaturated compounds because they contain a. single bonds only. b. double or triple bonds. c. oxygen atoms. d. hydrogen atoms.

41. 22.2 Section Quiz. 2. What is the correct name for a compound with a C-C-C=C-C carbon skeleton? a. 3-pentyne b. 2-pentene c. 3-pentene d. 4-pentene

42. 22.2 Section Quiz. 3. Which of the following substances is an alkyne? a. C6H12 b. C2H4 c. C2H2 d. C4H8

43. Structural Isomers • Compounds that have the same molecular formula, but different molecular structures, are called structural isomers • Butane and 2-methylpropane (made by breaking carbon off the end, and making it a branch in the middle) • Also have different properties, such as b.p., m.p., and reactivity

44. Structural Isomers of Butane, C4H10

45. Stereoisomers • Don’t forget that these structures are really 3-dimensional • stereoisomers- molecules of the same molecular structure that differ only in the arrangement of the atoms in space. Two types are a) geometric and b) optical

46. Geometric Isomers • There is a lack of rotation around a carbon to carbon multiple bond • has an important structural implication • Two possible arrangements: 1.trans configuration - substituted groups on opposite sides of double bond 2. cisconfiguration - same side

47. Geometric Isomers Substituted groups are on opposite sides of the double bond (in this case, one is above, the other is below) Trans-2-butene Substituted groups are on the same side of the double bond (in this case, both are above) Cis-2-butene

48. Geometric Isomers • Trans-2-butene and Cis-2-butene shown on page 705 • differ in the geometry of the substituted groups (to double bond) • like other structural isomers, have different physical and chemical properties ( note page 705-middle)

49. Geometric Isomers In the trans configuration, the methyl groups are on opposite sides of the double bond. In the cis configuration, the methyl groups are on the same side of the double bond.

50. Optical Isomers • Asymmetric carbon? C with 4 different groups attached. Conceptual Problem 22.4, p.706 • Molecules containing asymmetric carbons have “handedness”, and exist as stereoisomers. • Figure 22.9, page 705