Chapter 25 “Hydrocarbon Compounds” Chemistry Golden Valley High School Stephen L. Cotton

Section 25.1 Hydrocarbons OBJECTIVES: Describe the relationship between number of valence electrons and bonding in carbon.

Define and describe alkanes. Section 25.1 Hydrocarbons OBJECTIVES: Define and describe alkanes.

Relate the polarity of hydrocarbons to their solubility. Section 25.1 Hydrocarbons OBJECTIVES: Relate the polarity of hydrocarbons to their solubility.

Organic Chemistry and Hydrocarbons Organic originally meant 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: Hydrocarbons

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

Organic Chemistry and Hydrocarbons 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 -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 25.1, page 745 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

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 branched part

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 748 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 , )

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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

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Properties of 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”

Quiz Draw. 2,3 diethyl pentane 3,3, 4 tri-methyl octane 2,3 ethyl, methyl hexane Name C C C-C-C-C-C-C

Section 25.2 Unsaturated Hydrocarbons OBJECTIVES: Describe the difference between unsaturated and saturated hydrocarbons.

Section 25.2 Unsaturated 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 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.

Explain why structural isomers have different properties. Section 25.3 Isomers OBJECTIVES: Explain why structural isomers have different properties.

Describe the conditions under which geometric isomers are possible. Section 25.3 Isomers OBJECTIVES: Describe the conditions under which geometric isomers are possible.

Identify optical isomers. Section 25.3 Isomers 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 (make by breaking Carbon off the end, and making 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. cis configuration - 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 754 differ in the geometry of the substituted groups (to double bond) like other structural isomers, have different physical and chemical properties

Optical Isomers Asymmetric carbon? C with 4 different groups attached. Conceptual Problem 25.12, p.755 Molecules containing asymmetric carbons have “handedness”, and exist as stereoisomers.

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

Section 25.4 Hydrocarbon Rings OBJECTIVES: Identify cyclic ring structures.

Section 25.4 Hydrocarbon 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 759 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.760 Benzene derivatives possible: methylbenzene, 3-phenylhexane, ethylbenzene page 761

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 761) C C C C

Section 25.5 Hydrocarbons From Earth’s Crust OBJECTIVES: Identify three important fossil fuels and describe their origins.

Section 25.5 Hydrocarbons From Earth’s Crust OBJECTIVES: Describe the composition of natural gas, petroleum, and coal.

Section 25.5 Hydrocarbons 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

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

Petroleum It is separated by distillation into fractions, according to boiling pt. 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

Coal From huge fern trees and mosses decaying millions of years ago under great pressure of rocks / soil. 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

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%)

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

Note the man standing beside it BIG BRUTUS Dragline used to remove the overburden of a strip mining coal field near West Mineral, Kansas Note the man standing beside it

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

End of Chapter 25