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Chapter 25 Hydrocarbon Compounds. Section 25.1 Hydrocarbons l OBJECTIVES: –Describe the bonding in hydrocarbons.

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Presentation on theme: "Chapter 25 Hydrocarbon Compounds. Section 25.1 Hydrocarbons l OBJECTIVES: –Describe the bonding in hydrocarbons."— Presentation transcript:

1 Chapter 25 Hydrocarbon Compounds

2 Section 25.1 Hydrocarbons l OBJECTIVES: –Describe the bonding in hydrocarbons.

3 Section 25.1 Hydrocarbons l OBJECTIVES: –Distinguish between straight- chain and branched-chain alkanes.

4 Organic Chemistry and Hydrocarbons l Organic originally meant chemicals that came from organisms l 1828 German chemist Friedrich Wohler synthesized urea in a lab l Today, organic chemistry is the chemistry of virtually all compounds containing the element carbon

5 Organic Chemistry and Hydrocarbons l Over a million organic compounds, with a dazzling array of properties l Why so many? Carbon’s unique bonding ability! l Let’s start with the simplest of the organic compounds: Hydrocarbons

6 Organic Chemistry and Hydrocarbons l Hydrocarbons contain only two elements: hydrogen and carbon –simplest hydrocarbons called alkanes, which contain only single covalent bonds –methane (CH 4 ) with one carbon is the simplest alkane. It is the major component of natural gas

7 Organic Chemistry and Hydrocarbons l Review structural formula- p.744 l Carbon has 4 valence electrons, thus forms 4 covalent bonds –not only with other elements, but also forms bonds WITH ITSELF. l Ethane (C 2 H 6 ) is the simplest alkane with a carbon to carbon bond

8 Straight-Chain Alkanes l Straight-chain alkanes contain any number of carbon atoms, one after the other, in a chain -meaning one linked to the next C-C-C C-C-C-C etc. l Names of alkanes always will always end with -ane

9 Straight-Chain Alkanes l Combined with the -ane ending is a prefix for the number of carbons –Table 25.1, page 745 l Homologous series- a group of compounds that have a constant increment of change l In alkanes, it is: -CH 2 -

10 Straight-Chain Alkanes l Many alkanes used for fuels: methane, propane, butane, octane l 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 l Condensed structural formulas? Note examples on page 746

11 Naming Straight-Chain Alkanes l 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 l We sometimes still rely on common names, some of which are well-known

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

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14 Branched-Chain Alkanes l Branched-chain means that other elements besides hydrogen may be attached to the carbon –halogens, oxygen, nitrogen, sulfur, etc. –any atom that takes the place of a hydrogen on a parent hydrocarbon is called a substituent, or the branched part

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

16 Branched-Chain Alkanes l Rules for naming - page Longest chain is parent 2. Number so branches have low # 3. Give position number to branch 4. Prefix more than one branch 5. Alphabetize branches 6. Use proper punctuation ( -, )

17 Branched-Chain Alkanes l Sample 25-2, page 749 l From the name, draw the structure: 1. Find the parent, with the -ane 2. Number carbons on parent 3. Identify substituent groups; attach 4. Add remaining hydrogens Sample 25-3, page 750

18 Alkanes l 3-ethylpentane l 2,3,4-trimethylhexane l Since the electrons are shared equally, the molecule is nonpolar –thus, not attracted to water –oil (a hydrocarbon) not soluble in H 2 O –“like dissolves like”

19 Section 25.2 Unsaturated Hydrocarbons l OBJECTIVES: –Explain the difference between unsaturated and saturated hydrocarbons.

20 Section 25.2 Unsaturated Hydrocarbons l OBJECTIVES: –Differentiate between the structures of alkenes and alkynes.

21 Alkenes l Multiple bonds can also exist between the carbon atoms l Hydrocarbons containing carbon to carbon double bonds are called alkenes C=C C-C=C l Called “unsaturated” if they contain double or triple bonds

22 Naming Alkenes l Find longest parent that has the double bond in it l New ending: -ene l Number the chain, so that the double bond gets the lower number l Name and number the substituents l Samples on page 752

23 Alkynes l Hydrocarbons containing carbon to carbon triple bonds called alkynes -C C- l Alkynes are not plentiful in nature l Simplest is ethyne- common name acetylene (fuel for torches) l Table 25.2, page 753 for b.p. and m.p.

24 Section 25.3 Isomerism l OBJECTIVES: –Distinguish among structural, geometric, and stereoisomers.

25 Section 25.3 Isomerism l OBJECTIVES: –Identify the asymmetric carbon or carbons in stereoisomers.

26 Structural Isomers l Compounds that have the same molecular formula, but different molecular structures, are called structural isomers l Butane and 2-methylpropane l Also have different properties, such as b.p., m.p., and reactivity

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

28 Geometric Isomers l Trans-2-butene and Cis-2-butene shown on page 754 l differ only in the geometry of their substituted groups l like other structural isomers, have different physical and chemical properties (also note page 755-top)

29 Stereoisomers l Don’t forget that these structures are really 3-dimensional l stereoisomers- molecules of the same molecular structure that differ only in the arrangement of the atoms in space- bottom page 755 l Asymmetric carbon? C with 4 different groups attached (Sample 25-4, p.756)

30 Section 25.4 Hydrocarbon Rings l OBJECTIVES: –Identify common cyclic ring structures.

31 Section 25.4 Hydrocarbon Rings l OBJECTIVES: –Explain resonance in terms of the aromatic ring of benzene.

32 Cyclic Hydrocarbons l The two ends of the carbon chain are attached in a ring in a cyclic hydrocarbon –sample drawings on page 759 –named as “cyclo- ____” l hydrocarbon compounds that do NOT contain rings are known as aliphatic compounds

33 Aromatic Hydrocarbons l A special group of unsaturated cyclic hydrocarbons is known as arenes –contain single rings, or groups of rings –originally called “aromatic hydrocarbons”, because of pleasant odor –simplest arene is benzene (C 6 H 6 ) –Term “aromatic” applies to materials with bonding like that of benzene

34 Aromatic Hydrocarbons l Benzene is a six-carbon ring, with alternating double and single bonds –exhibits resonance, due to location of the double and single bonds-p.760 l Benzene derivatives possible: –methylbenzene, 3-phenylhexane, ethylbenzene- page 760

35 Aromatic Hydrocarbons l Benzene derivatives can have two or more substitutents: –1,2-dimethylbenzene –1,3-dimethylbenzene –1,4-dimethylbenzene l Can use ortho for 1,2; meta for 1,3; and para for 1,4 (page 761)

36 Section 25.5 Hydrocarbons from the Earth l OBJECTIVES: –Identify three important fossil fuels and describe their origins.

37 Section 25.5 Hydrocarbons from the Earth l OBJECTIVES: –Name some products obtained from natural gas, petroleum, and coal.

38 Natural Gas l Fossil fuels provide much of the world’s energy l Natural gas and petroleum contain mostly aliphatic (straight-chain) hydrocarbons l Natural gas is an important source of alkanes of low molecular mass

39 Natural Gas l Natural gas is typically: –80% methane, 10% ethane, 4% propane, and 2% butane with the remainder being nitrogen and higher molar mass hydrocarbons –also contains a small amount of He, and is one of it’s major sources

40 Natural Gas l Natural gas is prized for combustion, because with adequate oxygen, it burns with a hot, clean blue flame: –CH 4 + 2O 2  CO 2 + 2H 2 O + heat l Insufficient burning has a yellow flame, due to glowing carbon parts, as well as making carbon monoxide

41 Petroleum l The compounds found in petroleum (or crude oil) are more complex than those in natural gas l Usually straight-chain and branched-chain alkanes, with some aromatic compounds also l Crude oil must be refined (separated) before being used

42 Petroleum l It is separated by distillation into fractions, according to boiling pt. l Fractions containing higher molar mass can be “cracked” into more useful shorter chain components, such as gasoline and kerosene –involves catalyst and heat –starts materials for plastics and paints

43 Coal l From huge fern trees and mosses decaying millions of years ago under great pressure l Stages in coal formation: 1. Peat- soft, fibrous material much like decayed garden refuse; high water content. After drying will make a low-cost, smoky fuel

44 Coal 2. Lignite- peat left in the ground longer, loses it’s fibrous texture, and is also called brown coal –harder than peat; higher C content (50%); still has high water content 3. Bituminous, or soft coal- formed after more time; lower water content, higher C content (70-80%)

45 Coal 4. Anthracite, or hard coal –carbon content exceeding 80%, making it an excellent fuel source l Coal may be found close to the surface (strip-mined), or deep within the earth l Pollutants from coal are common; soot and sulfur problems

46 Coal l Coal may be distilled for many products –coal gas, coal tar, coke, and ammonia –further distilled into benzene, toluene, naphthalene, phenol, and pitch –Coke is almost pure carbon; produces intense heat and little or no smoke, thus used in industrial processes


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