© 2014 Pearson Education, Inc. Lecture Presentation Chapter 20 Organic Chemistry Sherril Soman Grand Valley State University

© 2014 Pearson Education, Inc.

Lecture Presentation

Chapter 20

Organic Chemistry

Sherril SomanGrand Valley State University


• Our sense of smell helps us identify food, people, and other organisms, and alerts us to dangers such as polluted air or spoiled food.

• Odorants must be volatile.• However, many volatile substances have no

scent at all.• Most common smells are caused by

organic molecules.• The study of compounds containing carbon

combined with one or more of the elements hydrogen, nitrogen, oxygen, and sulfur, including their properties and their reactions, is known as organic chemistry.

Fragrances and Odors



What Is Organic Chemistry?

• Organic chemistry is a branch of chemistry that focuses on compounds that contain carbon.– Except CO, CO2, carbonates, and carbides

• Even though organic compounds only contain a few elements, the unique ways carbon atoms can attach together to form molecules leads to millions of different organic compounds.


• Life as we know it is because of organic chemistry.

• Organic molecules can be very large and complex.

• It is this complexity of large organic molecules that allows the complex functions of the cells to occur.

The Chemistry of Life


• Organic compounds are easily decomposed into simpler substances by heating, but inorganic substances are not.

• Inorganic compounds were readily synthesized in the lab, but synthesis of organic compounds in the lab is hard.

Differences Between Organic and Inorganic Compounds


• Organic compounds tend to be molecular.• They are mainly composed of just six

nonmetallic elements.– C, H, O, N, S, and P

• Compounds are found in all three states.– Solids, liquids, and gases– Solids tend to have low melting points

• Solubility in water varies depending on which of the other elements are attached to C and how many there are.– CH3OH is miscible with water; C10H21OH is

insoluble.

What’s Special About Organic Compounds?


• Carbon atoms can do some unique things that other atoms cannot.

• Carbon can bond to as many as four other atoms.

• Bonds to carbon are very strong and nonreactive.

What’s So Special About Carbon?


• Carbon atoms can attach together in long chains.

• Carbon atoms can attach together to form rings.

• Carbon atoms can form single, double, or triple bonds.

What’s So Special About Carbon?


• Hydrocarbons contain only C and H.– Aliphatic or aromatic

• Insoluble in water– No polar bonds to attract water molecules

• Aliphatic hydrocarbons– Saturated or unsaturated aliphatics

• Saturated = alkanes; unsaturated = alkenes or alkynes

– May be chains or rings– Chains may be straight or branched.

• Aromatic hydrocarbons

Hydrocarbons




• Molecular formulas show the kinds of atoms in the molecule, but they do not show how they are attached.

• Structural formulas show you the attachment pattern in the molecule.

• Models not only show you the attachment pattern, but give you an idea about the shape of the molecule.

Formulas


• Attached atoms listed in order– Central atom with attached atoms

• Follow normal bonding patterns– Use to determine position of multiple bonds

• () used to indicate more than one identical group attached to same previous central atom– Unless () group is listed first, in which case

attached to next central atom

Condensed Structural Formulas


Uses of Hydrocarbons






Physical Properties of Aliphatic Hydrocarbons

• Boiling points and melting points increase as the size of the molecule increases.– Nonpolar molecules– Main attractive forces are dispersion forces

• Less dense than water

• Insoluble in water


Saturated Hydrocarbons

• A saturated hydrocarbon has all C─C single bonds.– It is saturated with hydrogens.

• Saturated aliphatic hydrocarbons are called alkanes.

• Chain alkanes have the general formula CnH2n+2.

• Ring alkanes have all C─C single bonds, but have fewer hydrogens than a chain with the same number of carbons.


• Unsaturated hydrocarbons have one or more C═C double bonds or C≡C triple bonds.

• Unsaturated aliphatic hydrocarbons that contain C═C are called alkenes.– The general formula of a monounsaturated chain alkene

is CnH2n.– Remove two more H for each additional double bond.

• Unsaturated aliphatic hydrocarbons that contain C≡C are called alkynes.– The general formula of an alkyne with one triple bond

is CnH2n−2.– Remove four more H for each additional triple bond.

Unsaturated Hydrocarbons


Aromatic Hydrocarbons

• Aromatic hydrocarbons contain a ring structure that seems to have C═C, but doesn’t behave that way.

• The most prevalent example is benzene.– C6H6

– Other compounds have the benzene ring with other groups substituted for some of the hydrogens.


• Each angle, and beginning and end, represent a C atom.

• H omitted on C– Included on functional groups

• Multiple bonds indicated– Double line is double bond; triple line is

triple bond

Carbon Skeleton Formulas


Formulas


• Isomers are different molecules with the same molecular formula.

• Structural isomers are isomers that have a different pattern of atom attachment.– Also known as constitutional isomers

• Stereoisomers are isomers with the same pattern of atom attachments, but the atoms have a different spatial orientation.

Isomerism


Butane, BP = 0 °C Isobutane, BP = −12 °C

Structural Isomers of C4H10


Rotation about a Bond Is Not Isomerism


Possible Structural Isomers


Stereoisomers

• Stereoisomers are different molecules whose atoms are connected in the same order, but with a different spatial direction.

• Optical isomers are stereoisomers that are nonsuperimposable mirror images of each other.

• Geometric isomers are stereoisomers that are not optical isomers.


Nonsuperimposable Mirror Images

The mirror image cannot be rotated so all its atoms align with the same atoms of the original molecule.


• Any molecule with a nonsuperimposable mirror image is said to be chiral.

• Any carbon with four different substituents will be a chiral center.

• A pair of nonsuperimposable mirror images are called a pair of enantiomers.

Chirality


Optical Isomers of 3-Methylhexane


• Light that has been filtered so that only those waves traveling in a single plane are allowed through

Plane Polarized Light


• Enantiomers have all the same physical properties except one—the direction they rotate the plane of plane-polarized light– Each one of the enantiomers will rotate the plane the

same amount, but in opposite directions.– Dextrorotatory = rotates the plane to the right– Levorotatory = rotates the plane to the left

Optical Activity


Mixtures of Enantiomers

• An equimolar mixture of a pair of enantiomers is called a racemic mixture.

• Because half the molecules are rotating the plane to the left and the other half are rotating it to the right, the rotations cancel, and the racemic mixture does not rotate the plane.

• If the mixture is nonracemic, the amount of rotation can be used to determine the percentages of each enantiomer in the mixture.


Chemical Behavior of Enantiomers

• A pair of enantiomers will have the same chemical reactivity in a nonchiral environment.

• But in a chiral environment they may exhibit different behaviors.– Enzyme selection of one enantiomer of a pair


• Also know as paraffins

• Aliphatic

• General formula CnH2n+2 for chains

• Very unreactive

• Come in chains or/and rings– CH3 groups at ends of chains, CH2 groups

in the middle

• Saturated

• Branched or unbranched

Alkanes




Physical Properties of n–Alkanes


• Each name consists of three parts– Prefix

• Indicates position, number, and type of branches • Indicates position, number, and type of each

functional group– Parent

• Indicates the length of the longest carbon chain or ring– Suffix

• Indicates the type of hydrocarbono -ane, -ene, -yne

• Certain functional groups

Naming


1. Find the longest continuous carbon chain. 2. Number the chain from end closest to a branch.

− If first branches are equal distance, use next substituent

3. Name branches as alkyl groups.− Locate each branch by preceding its name with

the carbon number on the chain.

4. List branches alphabetically.− Do not count n-, sec-, t-, count iso

5. Use prefix if more than one of same group present.− “Di-,” “tri-,” “tetra-,” “penta-,” “hexa-”− Do not count in alphabetizing

Naming Alkanes


Prefixes


Alkyl Groups


• Also known as olefins• Aliphatic, unsaturated

– C═C double bonds

• Formula for one double bond = CnH2n.

– Subtract 2 H from alkane for each double bond.

• Trigonal shape around C– Flat

• Polyunsaturated = many double bonds

Alkenes


Alkenes

ethene = ethylenepropene = propylene

Produced by ripening fruit

C CH

H H

H

C CH

H CH3

H

Used to make polyethylene Used to make polypropylene



• Pi bond electrons not held as tight as sigma; therefore, alkenes are more polarizable than alkanes.

• Cis generally more polar than trans• Trans lower boiling point• More carbon groups attached to the double

bond = higher boiling point.– For equal numbers of C

• Densities similar to alkanes• Trans higher melting point than cis

– Molecules are more symmetrical and pack better.

Physical Properties of Alkenes


• Also known as acetylenes

• Aliphatic, unsaturated

• CC triple bond

• Formula for one triple bond = CnH2n − 2.– Subtract 4 H from alkane for each triple bond.

• Linear shape

• Internal alkynes have both triple bond carbons attached to C.

• Terminal alkynes have one carbon attached to H.

Alkynes



Alkynes

Used in welding torches

Ethyne = acetylene


Physical Properties of Alkynes

• Higher boiling points than similar sized alkenes– Similar size = same number of carbons– More pi bond = more polarization = higher boiling point

• Slightly higher densities than similar alkenes

• There are no alkyne cis or trans isomers.

• Internal alkynes have higher boiling points than terminal alkynes.– With the same number of C


• Change suffix on main name from -ane to -ene for base name of alkene, or to -yne for the base name of the alkyne.

• Number chain from end closest to multiple bond.

• Number in front of main name indicates first carbon of multiple bond.

Naming Alkenes and Alkynes


Geometric Isomerism

• Because the rotation around a double bond is highly restricted, you will have different molecules if groups have different spatial orientation about the double bond.– Stereoisomers

• This is often called cis–trans isomerism.

• When groups on the doubly bonded carbons are cis, they are on the same side of the double bond.

• When groups on the doubly bonded carbons are trans, they are on opposite sides.


Cis–Trans Isomerism



Reactions of Hydrocarbons

• All hydrocarbons undergo combustion.

• Combustion is always exothermic.

– About 90% of U.S. energy generated by combustion

CH3CH2CH3(g) + 5 O2(g) → 3 CO2(g) + 4 H2O(g)

CH2═CHCH2CH3(g) + 6 O2(g) → 4 CO2(g) + 4 H2O(g)

CH≡CCH3(g) + 4 O2(g) → 3 CO2(g) + 2 H2O(g)


Chemical Energy

• Burning hydrocarbons releases heat and light energy.– Combustion

• Alkane + oxygen carbon dioxide + water

• Larger alkane, more heat released


• Substitution– Replace H with a halogen atom.– Initiated by addition of energy in the form of heat

or ultraviolet light

• To start breaking bonds– Generally get multiple products with multiple

substitutions– Methane + chlorine chloromethane + HCl

Alkane Reactions


Alkene and Alkyne Reactions: Addition

• Adding a molecule across the multiple bond

• Hydrogenation = adding H2

– Converts unsaturated molecule to saturated

– Alkene or alkyne + H2 → alkane

– Generally requires a catalyst

• Halogenation = adding X2

• Hydrohalogenation = adding HX– HX is polar.– When adding a polar reagent to a double or triple

bond, the positive part attaches to the carbon with the most H’s.


Addition Reactions


Aromatic Hydrocarbons

• Contain benzene ring structure

• Even though they are often drawn with C═C, they do not behave like alkenes.


Resonance Hybrid

• The true structure of benzene is a resonance hybrid of two structures.


• (Name of substituent)benzene– Halogen substituent = change ending to “o”

• Or name of a common derivative

Naming Monosubstituted Benzene Derivatives


Naming Benzene as a Substituent

• When the benzene ring is not the base name, it is called a phenyl group.


• Number the ring starting at attachment for first substituent, and then move toward the second.– Order substituents alphabetically.– Use “di-” if both substituents are the same.

Naming Disubstituted: Benzene Derivatives


• Alternatively, use relative position prefix.– Ortho- = 1,2; meta- = 1,3; para- = 1,4

2-chlorotolueneortho-chlorotoluene

o-chlorotoluene

3-chlorotoluenemeta-chlorotoluene

m-chlorotoluene

4-chlorotoluenepara-chlorotoluene

p-chlorotoluene

Naming Disubstituted: Benzene Derivatives


• Contain multiple benzene rings fused together– Fusing = sharing a common bond

Polycyclic Aromatic Hydrocarbons


• Other organic compounds are hydrocarbons in which functional groups have been substituted for hydrogens.

• A functional group is a group of atoms that shows a characteristic influence on the properties of the molecule.– Generally, the reactions that a compound will

perform are determined by what functional groups it has.

– Because the kind of hydrocarbon chain is irrelevant to the reactions, it may be indicated by the general symbol.

Functional Groups



• R—OH• Ethanol = CH3CH2OH

– Grain alcohol = fermentation of sugars in grains

– Alcoholic beverages• Proof number = 2 times percentage of

alcohol– Gasohol

• Isopropyl alcohol = (CH3)2CHOH– 2-propanol– Rubbing alcohol– Poisonous

• Methanol = CH3OH– Wood alcohol = thermolysis of wood– Paint solvent– Poisonous

Alcohols


• Main chain contains OH.• Number main chain from end closest to OH.• Give base name -ol ending and place

number of C on chain where OH attached in front.

• Name as hydroxy group if higher precedence group present.

Naming Alcohols


Nucleophilic substitutionCH3─OH + HCl CH3Cl + H2O

Acid catalyzed elimination (dehydration)

CH3─ CH2OH CH2═CH2 + H2OH2SO4

Reactions of Alcohols


Reactions of Alcohols

Oxidation

CH3CH2OH CH3CHO CH3COOH −2 H −2 H

A common oxidizing agent is Na2Cr2O7.

Alcohols with very active metals

2 CH3─OH + 2 K 2 CH3O−K+ + H2



• Contain the carbonyl group– Aldehydes = at least 1 side H– Ketones = both sides R groups

• Many aldehydes and ketones have pleasant tastes and aromas.

• Some are pheromones.• Formaldehyde = H2C=O

– Pungent gas– Formalin = a preservative– Wood smoke, carcinogenic

• Acetone = CH3C(=O)CH3

– Nail-polish remover

Aldehydes and Ketones




• Acetophenone = pistachio

• Carvone = spearmint

• Ionone = raspberries

• Muscone = musk

Ketone Odors and Flavors


• Main chain contains C═O.– Unless COOH present

• Number main chain from end closest to C═O.

• For aldehydes, give base name -al ending.– Always on C1

• For ketones, give base name -one ending and place number of C on chain where C═O attached in front.

Naming Aldehydes and Ketones


• Aldehydes and ketones are generally synthesized by the oxidation of alcohols.

• Therefore, reduction of an aldehyde or ketone results in an alcohol.

• Common reducing agents are H2 with a Ni catalyst, NaBH4, and LiAlH4.

Reactions





Reactions





Reactions


Carbonyl Group

C═O group is highly polar.Many reactions involve addition across C═O,

with positive part attached to O.


Addition to C═O

Polar molecules add across the C═O, with the positive part attaching

to O.

−


• RCOOH• Sour tasting• Weak acids• Citric acid

Found in citrus fruit

• Ethanoic acid = acetic acidVinegar

• Methanoic acid = formic acidInsect bites and stings

Carboxylic Acids


Synthesis of Carboxylic Acids

• Made by the oxidation of aldehydes and alcohols.


• Carboxylic acid group always on end of main chain– Has highest naming precedence of functional

groups

• C of group always C1– Position not indicated in name

• Change ending to -oic acid

Naming Carboxylic Acids


Examples of Naming Carboxylic Acids



• R—COO—R

• Sweet odor

• Made by reacting carboxylic acid with an alcoholRaCOOH + RbOH ⇔ RaCOORb + H2O

Esters


• Carboxylic acid group always on end of main chain– Unless carboxylic acid group present

• C of ester group on C1– Position not indicated in name

• Begin name with alkyl group attached to O.

• Name main chain with -oate ending.

Naming Esters


• A condensation reaction is any organic reaction driven by the removal of a small molecule, such as water.

• Esters are made by the condensation reaction between a carboxylic acid and an alcohol.

The reaction is acid catalyzed.

Condensation Reactions





• Acid anhydrides are made by the condensation reaction between to carboxylic acid molecules.

The reaction is driven by heat.




Synthesis of Aspirin(Acetylsalicylic Acid)


Ethers

• Ethers have the general formula ROR.

• The two R groups may be different or identical.


Ethers

• Diethyl ether is the most common ether.

• It is useful as a laboratory solvent and can dissolve many organic compounds.

• It has a low boiling point.


• N containing organic molecules• Very bad smelling• Form when proteins decompose• Organic bases• Name alkyl groups attached to the N, then

add -amine to the end.

Amines


• Many amines are biologically active.– Dopamine – a neurotransmitter– Epinephrine – an adrenal hormone– Pyridoxine – vitamin B6

• Alkaloids are plant products that are alkaline and biologically active.– Toxic– Coniine from hemlock– Cocaine from coca leaves– Nicotine from tobacco leaves– Mescaline from peyote cactus– Morphine from opium poppies

Amines


Amine Reactions

• Weak bases– React with strong acids to form ammonium salts

RNH2 + HCl → RNH3+Cl−

• React with carboxylic acids in a condensation reaction to form amides

RCOOH + H—NHR‘⇔ RCONHR’ + H2O


• Polymers are very large molecules made by repeated linking together of small molecules. – Monomers

Polymers


• Natural polymers are polymers found in both the living and nonliving environment.

• Modified natural polymers are natural polymers that have been chemically altered.

• Synthetic polymers are polymers made in a lab from one, two, or three small molecules linked in a repeating pattern.– Plastics, elastomers (rubber), fabrics, adhesives

• Composites are materials made of polymers mixed with various additives.– Additives such as graphite, glass, metallic flakes

Polymers


• Polysaccharides – polymers made of repeating small sugar molecule units – Cellulose (cotton) – Starch

• Proteins – polymers made of repeating amino acid units• Nucleic acids (DNA) – polymers made of repeating

nucleotide units• Natural latex rubber – polyisoprene• Shellac – a resin secreted by lac bugs• Gutta-percha – a polyisoprene latex from the sap of the

gutta-percha plant – Used to fill space for root canal

• Amber, lignin, pine rosin – resins from trees• Asphalt – polymeric petroleum

Natural Polymers



• Cellulose acetate – an ester of cellulose and acetic acid– Rayon – Film

• Vulcanized rubber – latex rubber hardened by cross-linking with sulfur

• Nitrocellulose – an ester of cellulose with nitric acid – Gun cotton– Celluloid

• Ping-Pong™ balls

• Casein – a polymer of the protein casein made by treating cow’s milk with acid – Buttons, moldings, adhesives

Modified Natural Polymers


Polymerization

• Polymerization is the process of linking the monomer units together.

• There are two processes by which polymerization may proceed—addition polymerization and condensation polymerization.

• Monomer units may link head to tail, or head to head, or tail to tail during polymerization.– Head to tail most common– Regular pattern gives stronger attractions between

chains than random arrangements



• Monomers add to the growing chain in such a manner that all the atoms in the original monomer wind up in the chain.– No other side products formed; no atoms

eliminated

• First monomer must “open” to start reaction.– Done with heat, or the addition of an initiator

• The process is a chain reaction.– Each added unit ready to add another

Addition Polymerization


Condensation Polymerization

• Monomer units are joined by removing small molecules from the combining units.– Polyesters, polyamides lose water

• No initiator is needed.

• The process is a chain reaction.

• Each monomer has two reactive ends, so the chain can grow in two directions.


• Transparent or translucent• Chemical resistance• Thermal and electrical insulators• Low density• Varying strengths

– Kevlar• Mold or extrude• Elasticity

– Regain original shape if quick stress applied• Foamed• Tend to soften when heated, rather than

quickly melt

Characteristics of Plastics

Documents

© 2014 Pearson Education, Inc. Lecture Presentation Chapter 20 Organic Chemistry Sherril Soman Grand Valley State University