Chapter 22 Hydrocarbon Compounds

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

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

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

Models of Methane

Organic Chemistry and Hydrocarbons l Review structural formula- p. 698 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

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 will always end with -ane

Straight-Chain Alkanes l Combined with the -ane ending is a prefix for the number of carbons –Table 22.1, page 700 l Homologous series- a group of compounds that have a constant increment of change l In alkanes, it is: -CH 2 -

Alkane Hydrocarbons

Alkane Prefixes – The root indicates the number of carbon atoms NameMolecular Form MethaneCH 4 EthaneC2H6C2H6 PropaneC3H8C3H8 ButaneC 4 H 10 PentaneC 5 H 12 HexaneC 6 H 14 HeptaneC 7 H 16 OctaneC 8 H 18 NonaneC 9 H 20 DecaneC 10 H 22

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 702

Alkane Melting and Boiling Points

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 –Methane is natural gas or swamp gas

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

Section 26.2 Alcohols and Ethers l OBJECTIVES: –Describe the structures and naming of alcohols and ethers.

Section 26.2 Alcohols and Ethers l OBJECTIVES: –Define an addition reaction, and give several examples.

Section 26.2 Alcohols and Ethers l OBJECTIVES: –Compare the properties of alcohols and ethers.

Functional Groups l Most organic chemistry involves replacing one or more of the hydrogen atoms with a ‘substituent group’ –Groups often contain C, O, N, S, or P –They are also called “functional groups”- the chemically functional part of the molecule. They change the properties or function of the molecule.

Functional Groups l Functional group - a specific arrangement of atoms in an organic compound, that is capable of characteristic chemical reactions. –What is the best way to classify organic compounds? By their functional groups.

Functional Groups l The symbol “R” is used to represent any carbon chains or rings l Table 23.1, page shows some of the major categories, and their functional groups l We will concentrate on the alcohol functional group.

Alcohols l Alcohols - a class of organic compounds with an -OH group –The -OH functional group in alcohols is called a “hydroxyl” group; thus R-OH is the formula l How is this different from the hydroxide ion with basics? (covalent bonding with carbon- not ionic with a metal such as sodium)

Methanol Structure

Ethanol Ball and Stick

Alcohols l Arranged into categories according to the number of R groups attached to the carbon with the hydroxyl –1 R group: primary alcohol –2 R groups: secondary alcohol –3 R groups: tertiary alcohol l Note drawings on page 778

Alcohols l Both IUPAC and common names l For IUPAC: –drop the -e ending of the parent alkane name; add ending of -ol, number the position of -OH –parent is the longest chain that contains the carbon with the hydroxyl attached.

Alcohols l The hydroxyl is given the lowest position number l Alcohols containing 2, 3, and 4 of the -OH substituents are named diols, triols, and tetrols respectively –Examples on page 779

Alcohols l Common names: –similar to halocarbons, meaning name the alkyl group followed by the word ‘alcohol’ –One carbon alcohol = methyl alcohol

Alcohols l More than one -OH substituents are called glycols (ethylene glycol?) l ** Examples on page 779 ** l Phenols - compounds in which a hydroxyl group is attached directly to an aromatic ring. Cresol is the common name of o, m, and p isomers of methylphenol

Properties of Alcohols l Much like water, alcohols are capable of hydrogen bonding between molecules –this means they will boil at a higher temp. than alkanes and halocarbons with a comparable number of atoms

Properties of Alcohols l Alcohols are derivates of water; the -OH comes from water, and thus are somewhat soluble l Alcohols of up to 4 carbons are soluble in all proportions; more than 4 carbons are usually less soluble, because…?

Properties of Alcohols l Many aliphatic alcohols used in laboratories, clinics, and industry –Isopropyl alcohol (2-propanol) is rubbing alcohol; used as antiseptic, and a base for perfume, creams, lotions, and other cosmetics l Ethylene glycol (1,2-ethanediol) - commonly sold as antifreeze

Properties of Alcohols l Glycerol (1,2,3-propanetriol) - used as a moistening agent in cosmetics, foods, and drugs; also a component of fats and oils l Ethyl alcohol (ethanol) used in the intoxicating beverages; an important industrial solvent

Properties of Alcohols l Denatured alcohol- means it has been made poisonous by the addition of other chemicals, often methyl alcohol (methanol, or wood alcohol). As little as 10 mL of methanol has been known to cause permanent blindness, and 30 mL has resulted in death!!!

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

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

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 ( -, )

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

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”

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

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

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” hydrocarbons if they contain double or triple bonds

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 711

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 22.5, page 715 for b.p. and m.p.

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

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

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

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

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)

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)

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

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

Cyclic Hydrocarbons l The two ends of the carbon chain are attached in a ring in a cyclic hydrocarbon –sample drawings on page 706 –named as “cyclo- ____” l hydrocarbon compounds that do NOT contain rings are known as aliphatic compounds

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

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

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)

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

Section 22.5 Hydrocarbons from the Earth l OBJECTIVES: –Identify three important fossil fuels and describe their origins.

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

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, that is recovered and used in various industries, including balloons

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

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

Petroleum Fractional Distillation

Crude Oil Components

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 –starter materials for plastics and paints

Petroleum Cracking

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

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 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

Scrubbing Sulfur From Coal

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