Chapter 20 Organic Chemistry Lecture Presentation Chapter 20 Organic Chemistry Sherril Soman Grand Valley State University

Fragrances and Odors 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.

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.

The Chemistry of Life 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.

Differences Between Organic and Inorganic Compounds 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.

What’s Special About Organic 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 So Special About Carbon? 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.

Hydrocarbons contain only C and H. Insoluble in water 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

Formulas 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.

Condensed Structural 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

Uses of Hydrocarbons

Uses of Hydrocarbons

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 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.

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.

Carbon Skeleton Formulas 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

Formulas

Isomers are different molecules with the same molecular formula. Isomerism 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.

Structural Isomers of C4H10 Butane, BP = 0 °C Isobutane, BP = −12 °C

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.

Chirality 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.

Optical Isomers of 3-Methylhexane

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

Optical Activity 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

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

General formula CnH2n+2 for chains Very unreactive Alkanes 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

Physical Properties of n–Alkanes

Each name consists of three parts Naming 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 hydrocarbon -ane, -ene, -yne Certain functional groups

Naming Alkanes 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

Prefixes

Alkyl Groups

Aliphatic, unsaturated Formula for one double bond = CnH2n. Alkenes 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 ethene = ethylene propene = propylene H H C C 3 Produced by ripening fruit Used to make polypropylene Used to make polyethylene

Physical Properties of Alkenes 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.

Also known as acetylenes Aliphatic, unsaturated CºC triple bond Alkynes Also known as acetylenes Aliphatic, unsaturated CºC 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 Ethyne = acetylene Used in welding torches

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

Naming Alkenes and Alkynes 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.

This is often called cis–trans isomerism. 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)

Burning hydrocarbons releases heat and light energy. Chemical Energy Burning hydrocarbons releases heat and light energy. Combustion Alkane + oxygen ® carbon dioxide + water Larger alkane, more heat released

Alkane Reactions Substitution To start breaking bonds 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

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.

Naming Monosubstituted Benzene Derivatives (Name of substituent)benzene Halogen substituent = change ending to “o” Or name of a common derivative

Naming Benzene as a Substituent When the benzene ring is not the base name, it is called a phenyl group.

Naming Disubstituted: Benzene Derivatives 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-chlorotoluene ortho-chlorotoluene o-chlorotoluene 3-chlorotoluene meta-chlorotoluene m-chlorotoluene 4-chlorotoluene para-chlorotoluene p-chlorotoluene

Polycyclic Aromatic Hydrocarbons Contain multiple benzene rings fused together Fusing = sharing a common bond

Functional Groups 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.

Isopropyl alcohol = (CH3)2CHOH Alcohols 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

Naming 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.

Nucleophilic substitution CH3─OH + HCl ® CH3Cl + H2O Reactions of Alcohols Nucleophilic substitution CH3─OH + HCl ® CH3Cl + H2O Acid catalyzed elimination (dehydration) CH3─ CH2OH ® CH2═CH2 + H2O H2SO4

Alcohols with very active metals Reactions of Alcohols Oxidation CH3CH2OH ® CH3CHO ® CH3COOH −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 and Ketones 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

Ketone Odors and Flavors Acetophenone = pistachio Carvone = spearmint Ionone = raspberries Muscone = musk

Naming Aldehydes and Ketones 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. 79

Reactions 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.

Therefore, reduction of an aldehyde or ketone results in an alcohol. Reactions 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. 81

Therefore, reduction of an aldehyde or ketone results in an alcohol. Reactions 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. 82

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. d+ d−

Ethanoic acid = acetic acid Methanoic acid = formic acid Carboxylic Acids RCOOH Sour tasting Weak acids Citric acid Found in citrus fruit Ethanoic acid = acetic acid Vinegar Methanoic acid = formic acid Insect bites and stings

Synthesis of Carboxylic Acids Made by the oxidation of aldehydes and alcohols.

Naming Carboxylic Acids 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

Examples of Naming Carboxylic Acids

RaCOOH + RbOH ⇔ RaCOORb + H2O Esters R—COO—R Sweet odor Made by reacting carboxylic acid with an alcohol RaCOOH + RbOH ⇔ RaCOORb + H2O

Carboxylic acid group always on end of main chain Naming 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.

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

Condensation Reactions A condensation reaction is any organic reaction driven by the removal of a small molecule, such as water. Acid anhydrides are made by the condensation reaction between to carboxylic acid molecules. The reaction is driven by heat. 94

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.

Amines 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.

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

RCOOH + H—NHR‘⇔ RCONHR’ + H2O 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 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

Natural 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

Modified 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

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

Addition Polymerization 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

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.

Characteristics of Plastics 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