Nivaldo J. Tro

http://www.cengage.com/chemistry/tro

Mark Erickson • Hartwick College

Chapter 6Organic Chemistry

Carbon• Of the millions of known compounds in our world, 95% have a

single element in common: CARBON.

• What is so special about carbon?

Carbon• Smallest member, and only nonmetal, of group 4A• Forms 4 covalent bonds• Forms single, double, and triple bonds• Bonds to itself, forming chains and rings

Organic Chemistry• The study of carbon-containing compounds and their

chemistry is called organic chemistry.

• The properties of carbon-containing molecules determine the properties of the substance they compose.

Organic vs. Inorganic• Early 1800s

– Organic Compounds• Came from living organisms• Chemically fragile• Unsuccessful synthesis . . . required a vital force?

– Inorganic Compounds• Came from the earth• Chemically durable• Successfully synthesized by 19th-century chemists

Urea• Synthesized by Friedrich Wohler

in 1828

• Organic, but synthesized from an inorganic compound

• Subsequent death of vitalism – The idea that life was

somehow beyond physical laws was proven wrong.

– Living organisms must follow the physical laws of the universe.

Organic Compounds

Two Major Types of Organic Compounds

• Hydrocarbons– Contain only carbon and hydrogen

• Functionalized Hydrocarbons– Hydrocarbons that contain additional atoms or groups of

atoms called functional groups

• Both groups can be further divided into subfamilies.

The Hydrocarbon Family• Alkanes

– Only single bonds

• Alkenes– One or more double bonds

• Alkynes– One or more triple bonds

• Aromatic– Six-membered rings with

alternating single and double bonds

Alkanes• All carbon atoms connected by single bonds

• General molecular formula: CnH2n+2

• Simplest is methane, CH4

• Each atom attains an octet; the molecular geometry of methane is tetrahedral.

• Example of larger alkanes:

C C C C H

H

H

H

H

H

H

H

H

H

C C C C C C H

H

H

H

H

H

H

H

H

H

H

H

H

H

Butane Hexane

Polarity of Hydrocarbons• Carbon-hydrogen bonds are mostly nonpolar but any polarity

would be symmetrically arranged about the central carbon atom(s).

• Methane’s tetrahedral geometry makes it a nonpolar molecule.– All other hydrocarbons are nonpolar as well.

• Nonpolar substances are unable to mix with polar substances.

Structural Formulas• Show the relative positions of atoms in a molecule

• Two-dimensional

• Similar to Lewis structures but dashes represent bonding electron pairs

• Condensed structural formulas are compactly written structural formulas.

• Example: Pentane (C5H12)

C C C C C H

H

H

H

H

H

H

H

H

H

H

H

Structural formula

CH3CH2CH2CH2CH3

Condensed structural formula

Propane Formulas

Alkanes

Alkanes

Naming Alkanes• Straight chain alkanes are

named with a base name reflecting the number of carbon atoms in the longest continuous chain and using the suffix -ane.

Concept Check 6.1• Give the molecular, structural, and condensed formulas for

the straight-chained alkanes with seven and eight carbons and name them.

Concept Check 6.1 SolutionC7H16: heptane

C8H18: octane

C C C C C C C

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

CH3CH2CH2CH2CH2CH2CH3

C C C C C C C

H

H

H

H

H

H

H

H

H

H

H

H

H

H

C

H

H

H

H

CH3CH2CH2CH2CH2CH2CH2CH3

Alkanes• The most important property of the alkanes is their

flammability, the combustion reaction between oxygen and the alkane that produces carbon dioxide and water.

Saturation• Alkanes are saturated; they contain the maximum number of

hydrogen atoms per carbon atom.

• Alkenes and alkynes are unsaturated. They contain at least one double or triple bond, respectively. They have fewer hydrogen atoms per carbon atom than alkanes.

Alkenes• Flammable and nonpolar like alkanes• Double bond makes them more chemically reactive than

alkanes by addition across the double bond.• Straight chain alkenes are named with a base name reflecting

the number of carbon atoms in the longest continuous carbon chain and using the suffix -ene. This chain is numbered from the end giving the C-C double bond the lowest possible number

Bananas exposed to ethene ripen faster.

C C

H

H

H

Hethene

Concept Check 6.2• Draw the structural formula for 1-hexene.

Concept Check 6.2 Solution• The hex prefix indicates that there are six carbons.

• The –ene ending indicates that it is an alkene (contains a carbon-carbon double bond).

• The “1” indicates where the double bond begins (on carbon #1), with the longest continuous carbon chain numbered from the end giving the double bond the lowest number.

C C C C C

H

H H

H

H

H

H

H

H

C1 2 3 4 5

H

H

H6

Alkenes

Alkynes• Like alkenes, not commonly encountered directly

• Ethyne (acetylene) is used in welding torches.

• Straight chain alkynes are named with a base name depending on the number of atoms in the longest carbon chain with the suffix –yne and numbered from the end giving the C-C triple bond the lowest possible number.

C CC C

H

H

H

H

H

H

2-butyne

Alkynes

Concept Check 6.3• Draw the structural formula for 1-hexyne.

Concept Check 6.3 Solution• The hex prefix indicates that there are six carbons.

• The –yne ending indicates that it is an alkyne (contains a carbon-carbon triple bond).

• The “1” indicates that the triple bond begins on carbon #1, with the longest continuous carbon chain numbered from the end giving the triple bond the lowest number.

C C C C CH

H

H

H

H

H

H

C1 2 3 4 5

H

H

H6

Isomers• It is possible for organic compounds to share a molecular

formula but have different structures based on the branching of the carbon chain.

• Isomers can differ in their physical and chemical properties.

Unsaturated Isomers• Alkenes and alkynes exhibit isomerism based on the position

of the multiple bond.

Naming Hydrocarbons: IUPAC RecommendationsAlkanes

– Determine the base name of the longest continuous carbon chain.

– Consider branches to be substituents of the base chain.

– Number the base chain beginning with the end closest to the first branch.

– Order the name:

• Number of the substituent followed by a dash

• Name of the substituent

• Base name of the compound

Concept Check 6.4• Name the following alkane:

CH3 CH2 CH CH2 CH2 CH3

CH3

Concept Check 6.4 Solution• The longest continuous carbon chain has six carbons and is

named hexane. It is numbered from the end giving the substituent the lowest possible number.

• Methyl substituent at carbon #3

• The compound is named 3-methylhexane

CH3 CH2 CH CH2 CH21 2 3 4 5

CH36

CH3

longest continuouscarbon chain

Numbering from this end gives the substituent the lowest possible number.

methyl substituent located on carbon #3

Naming Hydrocarbons:IUPAC Recommendations• When two or more substituents are present, number each and

list them alphabetically.

– Use a numbering system that contains the lowest possible numbers.

– For two or more substituents on the same carbon, use that number twice.

– Use prefixes to denote identical substituents.

Concept Check 6.5• Name the following alkane:

C C C C C C C

CH3

CH3

H

H

H

H

H

H

H

CH2CH3

H

H

H

H

H

H

Concept Check 6.5 Solution

• Heptane is the longest continuous carbon chain.• Two methyls and an ethyl branching substituents• Substituents named as 5-ethyl and 2,2-dimethyl

according to their positions on the chain, then listed alphabetically in the name.

C C C C C C C

CH3

CH3

H

H

H

H

H

H

H

CH2CH3

H

H

H

H

H

H

5-ethyl-2,2-dimethylheptane

1 2 3 4 5 6 7

Naming Alkenes and Alkynes• Similar to alkanes except for the addition of a number at the

beginning to indicate the position of the multiple bond(s)

1-butene 4-methyl-2-pentene

2-pentyne 5-ethyl-3-heptyne

Kekulé and Aromaticity• Early structure elucidation

– Carbon’s tendency toward four bonds

• Dreamed that he saw chains of six carbon atoms as snakes– One snake bit its own tail

• Proposed benzene as a ring of six carbon atoms

• Structure is still accepted today

Update on Kekulé’s Benzene Ring• Kekulé proposed a ring containing alternating double and

single bonds.• The bonds in benzene have since been found to be all of the

same length.• Each bond is now considered to be midway between a

double and a single bond.• Modern representation is a circle within a hexagon.

The Benzene Ring• Particularly stable

• When the ring contains substituents, it is called a phenyl ring.

• Also called aromatic ring due to the notable aroma of many compounds containing such a ring

• Two or more such rings fused together make polycyclic aromatic hydrocarbons.

Common Examples

Functionalized Hydrocarbons• Basic hydrocarbon structures form a foundation for a major

grouping of organic compounds.• Contain additional atoms or groups of atoms called functional

groups.• Insertion of functional groups to a hydrocarbon dramatically

alters its properties.

Representing Functionality• Compounds containing the same functional group are called a

family.

• Generic symbolism is R–FG where R is the hydrocarbon part of the molecule and FG is the functional group. – Symbol for an alcohol, R–OH.

• Functional groups help organize and classify organic compounds.

• Compounds with the same functional groups have similar chemical and physical properties.

Functionalized Hydrocarbons

Concept Check 6.6• For the following compound, identify the

functional group the name of its family.

C C C C

H

H

H

H H

O

H

H

OH

Concept Check 6.6 Solution• For the following compound, identify the

functional group the name of its family.

C C C C

H

H

H

H H

O

H

H

OH

Functionalgroup

Family: Carboxylic acids

Chlorinated Hydrocarbons• Found in pesticides, solvents, and refrigerant liquids• One or more chlorine atoms substitute for one or more

hydrogen atoms• Lower flammability and reactivity than hydrocarbons

DDT• Muller demonstrated

DDT’s effectiveness against insects and relative non-toxicity to humans.

• Stability made it efficient• Dramatically decreased

malaria in many countries• Muller awarded Nobel

Prize in 1948• Resistance and

bioamplification led to DDT’s ban.

CFCs• Chlorofluorocarbons are a subfamily of chlorinated

hydrocarbons.• Chemically stable . . .• Until they reach the high-energy sunlight in the upper

atmosphere• Ozone destruction led to bans.

Alcohols• General formula: R–OH

• Addition of the –OH makes alcohols polar.

• Increased intermolecular attractive forces make alcohols liquids.

• Naming involves modifying the hydrocarbon name with an ending of -ol.

Ethanol• Alcoholic beverages

• Gasoline additive

• Sugar fermentation

• CNS depressant

• Adverse health effects

Other Alcohols• Isopropyl alcohol is commonly known as rubbing alcohol.

• Methanol is toxic to the human liver.

• Ethanol is administered as an antidote.

Aldehydes and Ketones• Commonly found in pleasant flavors and aromas

• Contain the carbonyl group: carbon double bonded to an oxygen atom

Formulas• Aldehydes

– General formula: RCHO, includes carbonyl group

– Named according to length of the carbon chain with the ending of -al or -aldehyde

– Methanal (formaldehyde) is the simplest aldehyde.

• Preservation of biological specimens

Formulas• Ketones

– Similar to aldehydes but have two R groups with the carbonyl

– Names end in -one– Acetone is the simplest

ketone.

• Fingernail polish remover

Carboxylic Acids• Commonly found in

sour foods• General formula:

RCOOH• One oxygen atom is

bonded as a carbonyl group (C=O), and the other is an –OH group.

Esters• Esters have pleasant odors.

• General formula: R–COO–R′, where R can be a hydrocarbon or a hydrogen atom, R′ must be a hydrocarbon.

• Esters are named according to the relevant R and R′ groups, and have an –ate ending.

Ethers• Ethers contain the functional group –O–.• General formula: R–O–R′ where R and R′ are

hydrocarbons.• Named according to the R and R′ groups and given

the ending -ether

Amines• Amines are organic compounds that contain nitrogen.

• General formula: NR3 (R can be a hydrocarbon or a hydrogen atom)

• Notable for disagreeable odors

• Named for R groups present and ending in -amine

Concept Check 6.7• Match each the following compounds with the

following families: ketone, aldehyde, ester, carboxylic acid, alcohol, and amine.

C

O

HCH3CH2CH2CH2OH CH3CH2CH2NH2

CH3CH2CCH3

O

CH3CH2COCH2CH3

O

CH3CH2COH

O

Concept Check 6.7 Solution• The functional groups are circled.

C

O

HCH3CH2CH2CH2OH CH3CH2CH2NH2

CH3CH2CCH3

O

CH3CH2COCH2CH3

O

CH3CH2COH

O

aldehyde alcohol amine

ketone ester carboxylic acid

Chapter SummaryMolecular Concept

• Organic vs. inorganic

• Hydrocarbons

• Alkanes

• Alkenes

• Alkynes

• IUPAC naming

• Other functional groups

Societal Impact

• Organic compounds make our everyday lives possible.

• Hydrocarbons are the primary molecules our society uses for fuel.