Chapter 22 “Hydrocarbon Compounds”

Chapter 22“Hydrocarbon Compounds” Pre-AP Chemistry Charles Page High School Stephen L. Cotton (C4H10)

Section 22.1Hydrocarbons • OBJECTIVES: • Describe the relationship between number of valence electrons and bonding in carbon.

Section 22.1Hydrocarbons • OBJECTIVES: • Define and describe alkanes.

Section 22.1Hydrocarbons • OBJECTIVES: • Relate the polarity of hydrocarbons to their solubility.

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

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

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

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

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

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

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)

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

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

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

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

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

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 , )

- Page 699

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

- Page 700

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”

Section 22.2Unsaturated Hydrocarbons • OBJECTIVES: • Describe the difference between unsaturated and saturated hydrocarbons.

Section 22.2Unsaturated Hydrocarbons • OBJECTIVES: • Distinguish the structures of alkenes and alkynes.

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

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

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

Section 22.3Isomers • OBJECTIVES: • Explain why structural isomers have different properties.

Section 22.3Isomers • OBJECTIVES: • Describe the conditions under which geometric isomers are possible.

Section 22.3Isomers • OBJECTIVES: • Identify optical isomers.

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

Structural Isomers of Butane, C4H10

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

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

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

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)

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

Optical Isomers, and these will each show an asymetric carbon (4 different branches attached) The asymetric carbon

Section 22.4Hydrocarbon Rings • OBJECTIVES: • Identify cyclic ring structures.

Section 22.4Hydrocarbon Rings • OBJECTIVES: • Describe bonding in benzene.

Cyclic Hydrocarbons • The two ends of the carbon chain are attached in a ring in a cyclic hydrocarbon • sample drawings on page 709 • named as “cyclo- ____” • hydrocarbon compounds that do NOT contain rings are known as aliphatic compounds

Aromatic Hydrocarbons • A special group of unsaturated cyclic hydrocarbons is known as arenes • contain single rings, or groups of rings • also called “aromatic hydrocarbons”, because of pleasant odor • simplest aromatic is benzene (C6H6) • Term “aromatic” applies to materials with bonding like that of benzene

Aromatic Hydrocarbons • Benzene is a six-carbon ring, with alternating double and single bonds • exhibits resonance, due to location of the double and single bonds-p.710 • Benzene derivatives possible: • methylbenzene, 3-phenylhexane, ethylbenzene (top page 711)

Aromatic Hydrocarbons • One derivative of Benzene is called phenylethene, or commonly named STYRENE. • Foamed styrene is trademarked by Dow Chemical as “styrofoam” • Other manufacturers items usually just called “foam cups” CH2 CH

Aromatic Hydrocarbons • Benzene derivatives can have two or more substitutents: • 1,2-dimethylbenzene • 1,3-dimethylbenzene • 1,4-dimethylbenzene • Can use ortho for 1,2; meta for 1,3; and para for 1,4 (page 711) C C C C

Section 22.5Hydrocarbons From Earth’s Crust • OBJECTIVES: • Identify three important fossil fuels and describe their origins.

Section 22.5Hydrocarbons From Earth’s Crust • OBJECTIVES: • Describe the composition of natural gas, petroleum, and coal.

Section 22.5Hydrocarbons From Earth’s Crust • OBJECTIVES: • Describe what happens when petroleum is refined.

Natural Gas • Fossil fuels provide much of the world’s energy • Natural gas and petroleum contain mostly the aliphatic (or straight-chain) hydrocarbons – formed from marine life buried in sediment of the oceans • Natural gas is an important source of alkanes of low molecular mass

Natural Gas • 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

Natural Gas • Natural gas is prized for combustion, because with adequate oxygen, it burns with a hot, clean blue flame: • CH4 + 2O2 CO2 + 2H2O + heat • Incomplete burning has a yellow flame, due to glowing carbon parts, as well as making carbon monoxide

Chapter 22 “Hydrocarbon Compounds”