Chapter 22 “Hydrocarbon Compounds”

Mr. GowerTroy High School

(C4H10)

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 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

• 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

Organic Chemistry and Hydrocarbons

One carbon atom can form a single covalent bond with four hydrogen atoms.

Organic Chemistry and Hydrocarbons

Ball-and-stick model

Space-filling model

Formulas and Models for Methane and Ethane

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

AlkanesStraight-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.

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)

AlkanesA 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.

Alkane MP and BP- Van der Waals Forces.

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

Alkanes

Naming Straight-Chain Alkanes

• Names recommended by IUPAC - the International Union of Pure and Applied Chemistryend 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

Alkanes

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

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 6981. Longest C-C chain is parent2. Number so branches have lowest #3. Give position number to branch4. Prefix (di, tri) more than one branch5. 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 -ane2. Number carbons on parent3. Identify substituent groups (give

lowest number); attach4. Add remaining hydrogens

- Page 700

Alkanes

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

Practice- page 699

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”

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

22.1 Section Quiz.

2. Alkanes are hydrocarbons that contain only ___________ bonds.

a. carbon-carbon

b. single covalent

c. carbon-hydrogen

d. ionic

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

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

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

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

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

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.

Alkynes

Straight-chain and branched-chain alkanes, alkenes, and alkynes are aliphatic hydrocarbons.

Alkenes and alkynes are unsaturated!

Alkenes

Alkynes

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

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.

22.2 Section Quiz.

22.2 Section Quiz.

2. What is the correct name for a compound with a C-C-C=C-C carbon skeleton?

a. 3-pentyneb. 2-pentenec. 3-pentened. 4-pentene

22.2 Section Quiz.

3. Which of the following substances is an alkyne?

a. C6H12

b. C2H4

c. C2H2

d. C4H8

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. cis configuration - same side

Substituted groups are on opposite sides of the double bond (in this case, one is above, the other is below)

Substituted groups are on the same side of the double bond (in this case, both are above)

Geometric Isomers

Trans-2-butene

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)

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.

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

Stereoisomers

1. Structural isomers have different properties because they have

a. a different number of bonds.b. different types of bonds.c. different substituents.d. a different order of atoms.

22.3 Section Quiz

2. Substituent groups on opposite sides of a double bond are said to be in the _______ configuration. If the groups are on the same side of the bond, then they are in the _______ configuration.

a. cis, transb. trans, cisc. trans, isod. stereo, cis

22.3 Section Quiz

3. Geometric isomers have different arrangements of atoms

a. and different molecular formulas.

b. but only single bonds.c. around an asymetric carbon.d. around a double bond.

22.3 Section Quiz

4. A carbon atom that has four different substituents always forms

a. an optical isomer.b. a saturated hydrocarbon.c. a geometric isomer.d. an unsaturated hydrocarbon.

22.3 Section Quiz

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

Cyclic HydrocarbonsThree Ways to Represent Cyclic Hydrocarbons

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

The Structure of Benzene•Benzene can be shown as switching, or resonating, between two arrangements of alternating double and single bonds.

Aromatic HydrocarbonsThe three symbols below can be used to represent the benzene ring. If the bonds are shown as alternating single and double bonds (on right), it is important to remember that bonds don’t actually alternate and that all six bonds are identical.

Aromatic Hydrocarbons

Space-filling Model of Benzene

Aromatic HydrocarbonsSubstituted Aromatic Compounds

Compounds with a substituent on a benzene ring are named as a derivative of benzene. When benzene is a substituent, it is called a phenyl group.

Aromatic Hydrocarbons

A benzene ring can have two or more substituents.

Aromatic HydrocarbonsThe molecules of many dyes include benzene rings.

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”

CHCH2

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

CC

22.4 Section Quiz.1. Choose the correct words for the spaces. Alkanes that do not contain a ring structure are _______ hydrocarbons. Alkanes that do contain ring structures are called _________ hydrocarbons.

a. aliphatic, aromaticb. aromatic, aliphaticc. aliphatic, cyclicd. aromatic, cyclic

22.4 Section Quiz.

2. The carbon-carbon bonds in a benzene molecule are

a. alternating double and single bonds.b. identical hybrid bonds.c. all double bonds.d. all single bonds.

22.4 Section Quiz.

3. When an alkane has a benzene ring as a substituent, the ring is called _______ group.

a. a benzeneb. a toluenec. a phenyld. an arene

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

Natural Gas

Wells are drilled to reach natural gas and petroleum.

22.5

Petroleum

In fractional distillation, the crude oil is heated so that it vaporizes and rises through the fractionating column. The column is hotter at the bottom and cooler at the top.

22.5

Petroleum

22.5

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

CoalCoal Formation

• Coal formed when tree ferns and mosses died and were subjected to continued pressure and heat underground.

22.5

Coal

Coal consists largely of condensed aromatic compounds of extremely high molar mass. These compounds have a high proportion of carbon compared with hydrogen.

22.5

Coal

•Coal is mined from both surface mines and underground mines.

22.5

BIG BRUTUS

Dragline used to remove the overburden of a strip mining coal field near West Mineral,

Kansas.

Note the size of the man

standing next to 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