Carbon: More than Just Another Element Lectures written by John Kotz Chemistry and Chemical Reactivity 6th Edition John C. Kotz Paul M. Treichel Gabriela C. Weaver CHAPTER 11 Carbon: More than Just Another Element Lectures written by John Kotz © 2006 Brooks/Cole Thomson

ORGANIC CHEMISTRY

cinnamaldehyde eugenol

Types of Organic Compounds Vast majority of over 20 million known compounds are based on C: organic compounds. Generally contain C and H + other elements Great variety of compounds

Isomerism Isomers have identical composition but different structures Two forms of isomerism Constitutional (or structural) Stereoisomerism Constitutional Same empirical formula but different atom-to-atom connections Same atom-to-atom connections but different arrangement in space.

Structural Isomers

Stereoisomers: Geometric Geometric isomers can occur when there is a C=C double bond. Trans-2-butene Cis-2-butene

Stereoisomers: Optical Optical isomers are molecules with non-superimposable mirror images. Such molecules are called CHIRAL Pairs of chiral molecules are enantiomers. Chiral molecules in solution can rotate the plane of plane polarized light.

Chiral Compounds—Polarized Light

Stereoisomers Isomers Chirality generally occurs when a C atom has 4 different groups attached. Lactic acid

Stereoisomers Isomers Lactic acid isomers are nonsuperimposable

Chirality: Handedness in Nature These molecules are non-superimposable mirror images.

Chirality: Handedness in Nature These amino acids are non-superimposable mirror images.

Stereoisomers in Nature Right- and left-handed seashells The DNA here is right-handed

The egg cases of the whelk have a right-handed twist.

Hydrocarbons Compounds of C and H Subgroups: Alkanes: C-C single bonds Alkenes: C=C double bonds Alkynes: carbon-carbon triple bonds Aromatic: based on benzene

Hydrocarbons Alkanes have the general formula CnH2n+2 CH4 = methane C2H6 = ethane C3H8 = propane C4H10 = butane C5H12 = pentane

Methane Hydrate, CH4(H2O)x

A colony of worms on an outcropping of methane hydrate on the ocean floor. See the interchapter “The Chemistry of Fuels and Energy Sources”

Hydrocarbons & Structural Isomerism Isomers of C5H12? C5H12 has 3 structural isomers. C6H14 has 5 C7H14 has 9 Note names of isomers

Hydrocarbons: Alkanes Alkanes are colorless gases, liquids, and solids Generally unreactive (but undergo combustion) Not polar (or low polarity) and so are not soluble in water.

Hydrocarbons: Cycloalkanes All compounds are flexible. Cyclohexane, C6H12, has interconverting “chair” and “boat” forms.

Alkenes: Compounds with C=C Double Bonds How many isomers are possible for a compound with the formula C4H8?

Alkenes— Many Occur Naturally

Reactions of Alkenes: ADDITION REACTIONS Alkenes are unsaturated — more bonds can form to the C atoms Molecules such as Br2, H2, HCl, HBr, and H2O add to the double bond

An Addition Reaction Fat placed in Br2 vapor The fat in bacon is partially unsaturated. The fat adds Br2 to the C=C bonds. Fats can be “hydrogenated” with H2.

An Addition Reaction Fat placed in Br2 vapor

An Addition Reaction Fats can be “hydrogenated” with H2. Peanut butter has partially hydrogenated vegetable oil.

Trans Fatty Acids tend to raise total blood cholesterol CH3(CH2)7CH=CH(CH2)7CO2H Trans Fatty Acids tend to raise total blood cholesterol

Trans Fatty Acids Food Percentages of Trans-Fatty Acids Butter 3.6 Soft Margarine 5.2 Hard Margarine 12.4 Vegetable Oils, Including Safflower, Sunflower, and Soy Beefburger, Fried or Grilled 0.8 Chocolate Cake with Icing 7.1

Alkynes Alkynes have carbon-carbon triple bonds. C2H2: common name = acetylene systematic name = ethyne Preparation: CaC2(s) + H2O(liq) --> C2H2 (g) + Ca(OH)2(s) ∆Hfo(C2H2, g) = +226.7 kJ/mol ∆Hrxn for C2H2 + O2 = –1300 kJ/mol

Aromatic Compounds Benzene, C6H6, in the top 25 chemicals produced in the U.S. Starting point for hundreds of other compounds.

Resonance in Benzene C6H6 has two resonance structures with alternating double bonds. The π electrons are delocalized over the ring.

Resonance in Benzene CC bond order is _______________ C–C single bond = 154 pm C=C bond = 134 pm CC bonds in benzene = 139 pm π electrons delocalized

Bonding in Benzene

Other Aromatic Hydrocarbons Toluene Naphthalene

Benzene Derivatives Aniline Phenol TNT trinitrotoluene C6H5NH2 C6H5OH C6H4CH3(NO2)3

Naming Benzene Derivatives 1,4-dimethylbenzene Common name: Para-xylene

Reactions of Aromatics Substitutions — not additions — are typical. AlCl3 is a catalyst. Catalysts typically used in aromatic substitutions.

Functional Groups See CD-ROM Screens 11.5 & 11.6

Alcohols Characterized by –OH group Name: add –ol to name of hydrocarbon Methanol Butanol

Structures of Alcohols C3H5OH: how many structural isomers? Naming: Add -ol to name of 3-C hydrocarbon. Indicate position of OH with number.

Alcohol Properties Alcohols are a derivative of water Many alcohols dissolve in water Methanol dissolves in water. Butanol is NOT soluble in water.

“Sterno” Alcohols burn in air A mixture of ethanol + calcium acetate = STERNO

GLYCOLS Alcohols with Two OH Groups Propylene glycol Ethylene glycol

Alcohol Reactions Screen 11.6 Substitution Elimination—the reverse of addition

TYPES OF ALCOHOLS

More Alcohol Reactions Ethanol is a PRIMARY ALCOHOL. It is oxidized to an ALDEHYDE and then to an ACID.

More Alcohol Reactions SECONDARY ALCOHOLS are oxidized to KETONES — and reaction stops there.

Sugars: Related to Alcohols Sugars are carbohydrates, compounds with the formula Cx(H2O)y. What is the difference between a and b D-glucose?

Sucrose and Ribose Deoxyribose, the sugar in the DNA backbone.

Amines Alcohols are derivatives of H2O (R–OH) and amines are derivatives of NH3. Trimethylamine Dimethylamine Methylamine

Amines generally have terrible odors! Pyridine Cadaverine

Amines, like NH3, are bases

Amines Many natural products and drugs (such as nicotine and cocaine) are bases. H+ Nicotine

Compounds with Carbonyl Group Aldehyde Carboxylic acid Ketone

Structures of Aldehydes Cinnamaldehyde Odors from aldehydes and ketones

Carboxylic acid group with acidic H+ Carboxylic Acids Benzoic acid Acetic acid Carboxylic acid group with acidic H+ All are WEAK acids Acids are found in many natural substances: bread, fruits, milk, wine

Formic acid, HCO2H, gives the sting to ants. Carboxylic Acids Aspirin, acetylsalicylic acid

Acids + Alcohols --> ESTERS Esters have generally pleasant odors

Acids + Alcohols --> ESTERS One of the important reactions in nature!

Acids + Alcohols --> ESTERS Many fruits such as bananas and strawberries contain esters.

Glycerol Alcohol with 3 OH Groups Combine this with long chain acids ------> ??? Fatty acids ---> fats and oils

Fats and Oils R = organic group with NO C=C bonds C12 = Lauric acid C16 = Palmitic acid C18 = Stearic acid What is the functional group in a fat or oil? R = organic group with C=C bonds C18 = oleic acid

Fats with C=C bonds are usually LIQUDS Fats and Oils Fats with C=C bonds are usually LIQUDS Oleic acid: a monounsaturated fatty acid C=C bond

Fats and Oils Fats with saturated acids (no C=C bonds) are SOLIDS. Saturated fats are more common in animals.

Fats and Polar Bears Bears gorge on blubber in the winter. During the summer bears rely on stored fat for energy. Burn 1-1.5 kg of fat per day. Water for metabolism comes from fat burning.

Trans Fatty Acids Oleic acid is a mono–unsaturated cis-fatty acid Trans fatty acids have deleterious health effects. Trans fatty acids raise plasma LDL cholesterol and lower HDL levels. C=C bond

Fats and Oils: Saponification

Acids + Amines --> AMIDES N-methylacetamide

Acids + Amines --> AMIDES Acetoaminophen Tylenol, Datril, Momentum, ...

Alpha-Amino Acids

Peptides and Proteins – H2O Adding more peptide links ---> PROTEIN

Polymers Giant molecules made by joining many small molecules called monomers Average production is 150 kg per person annually in the U.S.

Polymer Classifications Thermoplastics (polyethylene) soften and flow when heated Thermosetting plastics — soft initially but set to solid when heated. Cannot be resoftened. Other classification: plastics, fibers, elastomers, coatings, adhesives

Polymer Preparation Addition polymers — directly adding monomer units together Condensation polymers — combining monomer units and splitting out a small water (water)

Polyethylene: Addition Polymer A polymer with a molar mass of 1e6 has about 360,000 units.

Mechanism of Addition Polymerization

Types of Polyethylene Linear, high density PE (HDPE) Branched, low density PE, LDPE Cross-linked PE, CLPE

Types of Polyethylene Table 11.12: others are PVC, acrylonitrile, polypropylene, polymethyl methacrylate

Polystyrene Polystyrene is nonpolar material and dissolves in organic solvents. PS foam is mostly air, and when it dissolves it collapses to a much smaller volume.

Slime! Slime is polyvinylalcohol cross-linked with boric acid

Bubble Gum! A copolymer Styrene + butadiene

Condensation Polymers

Polyesters, PET Jackets made from recycled PET soda bottles Soda bottles, mylar film.

Polyesters: Mechanism

Polyamides: Nylon

Polyamides: Nylon Each monomer has 6 C atoms in its chain. A polyamide link forms on elmination of HCl Result = nylon 66 Proteins are polyamides

Polymer Recycling Symbols LDPE = Low density PE = 0.910-0.925 g/cm3 HDPE = High density PE = 0.941-0.965 PP = Polypropylene = 0.90 V = PVC (Vinyl chloride) = 1.30-1.58