Chapter 21

Functional Groups and Classes of Organic Compounds

  1. Introduction

    A functional group - definition

    bonds within functional groups are usually where chemical reactivity takes place

    functional groups undergo the same type of chemical reaction, no matter what molecule you find the functional group

    compounds that contain the same functional group will have similar properties and can be grouped and studied as a group.

    1. Alcohols
      alcohols - definition

      R-OH is the general formula

      Rules for alcohol nomenclature p 663

      Examples of naming alcohols p 664

      1. Properties and Uses of Alcohols
        Table 21-1 p 664

        higher bp than alkanes of similar molecular masses but totally different bp’s e.g. ethanol v propane

        bp of alcohols increase as the number of hyroxyl groups increases in a molecule

        Table 21-2 p 664 - Multiple Hyroxyl Groups and Boiling Points

        bp trends can be explained by hydrogen bonding - extra energy needed to break hydrogen bonds between alcohol molecules before conversion from a liquid to a gas

        more than one hydroxyl group may mean more than one hydrogen bond

        alcohols are generally soluble in water because of the hydrogen bonding

        solubility decreases as size of molecule increases because the portion of the chain which is nonpolar is increasing in size

        table 21-3 p 665 _ Solubility of Some Alcohols in Water

        Glycerol is 1,2,3-propanetriol which forms multiple hydrogen bonds with water in air or in surrounding material - reason it is in cold creams, lipsticks, body lotions, etc. Keeps moisture near itself and on whatever it is spread

        figure 21-1 page 665 - Glycerol model and products

        alcohols are used as alternative fuels and as octane enhancers: gasohol is a mixture of ethanol and gasoline in a one to nine ratio. Gasohol produces 60% as much energy per gram as does the combustion of gasoline and it increases water absorption in the fuel. It does burn more cleanly and using it decreases the amount of petroleum used.

        Simple alcohols are poisonous to some extent. Ethanol (in alcoholic beverages) is broken down by alcohol dehydrogenase to a a compound, acetaldehyde, which is converted to acetic acid in the body. Acetic acid is found in vinegar and in small amounts is harmless. But the amount produced by consuming a liter of hard liquor is usually fatal.

        Other alcohols are converted into more toxic compounds. e.g. methanol (wood alcohol) is converted t formaldehyde and formic acid, both of which are toxic. Toxic effects of methanol include damage to the optic nerve, coma, and death.

    2. Alkyl Halides

      alkyl halides - definition

      X used to represent halogen

      R-X is the general formula for alkyl halides

      Alkyl Halide Nomenclature - p 666

      Sample Problem 21-1 p 667

      1. Properties and Uses of Alkyl Halides

        some of the most widely used organic compounds

        e.g. CFC’s or chlorofluorocarbons - alkyl halides that contain fluorine and chlorine

        Freon-11 and Freon-12 p 668

        Figure 21-2 p 668

        Both are odorless, nontoxic, nonflammable and very stable. They change physical states easily. Used to manufacture plastic foam and used as liquid refrigerants (currently banned for that purpose). When they get into the atmosphere they destroy the ozone layer in the upper atmosphere in the following way

        CCl2F2 + solar radiation ----> Cl + CClF2

        Cl + O3 ----> ClO + O2

        ClO + O ----> Cl + O2 and step 2 continues
        Ozone absorbs ultraviolet radiation. The less ozone there is the more radiation reaches us which can increase the occurrence of skin cancer.

        Tetrafluoethene, C2F4, is teflon. It is inactive and stable to about 325oC.

        Figure 21-3 p 669

    3. Ethers
      ethers - definition

      general formula: R - O - R where the two R’s may be the same or different hydrocarbon group

      Ether nomenclature p 670

      Sample Problem 21-2 p 670

      1. Properties and Uses of Ethers

        Solubilities of ethers and alcohols in water are similar because ethers can also form hydrogen bonds with water molecules.

        boiling points of ethers is much lower than alcohols of similar mass but about the same as alkanes of similar mass

        Table 21-4 p 671 - Comparison of the BP’s of an Ether, Alkane, and Alcohols

        Ethers cannot form hydrogen bonds with each other since they do nt have a hydrogen atom bonded to a highly electronegative atom. Thus, no extra energy is needed to break hydrogen bonds for ethers to boil.

        Ethers are not very reactive. Thus they are used as solvents where water cannot be used.

        MTBE, methyl-tertiary-butyl ether is the most widely used ether. It is a gasoline octane enhancer. It replaced tetraethyl lead.

        Homework 21.1

  2. More Classes of Organic Compounds

    1. Aldehydes and Ketones

      Both of these contain the carbonyl group.

      Carbonyl group - definition

      p 672 carbonyl group

      Where it is located distinguishes aldehydes from ketones.

      aldehydes - definition

      ketones - definition

      General formula for aldehydes and ketones p 672

      Aldehyde Nomenclature p 672

      Examples of aldehydes p 672

      Ketone Nomenclature p 672

      Examples of ketones p 673

      1. Properties and Uses of Aldehydes and Ketones

        Simplest aldehyde is methanal or formaldehyde which was used to preserve dead animals and in certain types of insulation. Also used to make plastics such as bakelite which is made from formaldehyde and phenol.

        Simplest ketone is propanone or acetone. Found in nail polish removers because it dissolves substances in nail polish. Used less in this capacity.

        Both classes of compounds are used for odors and flavors. Cinnamaldehde contributes to the odor and flavor of cinnamon.

        Figure 21-4 p 673 Examples of odors and flavors that come from aldehydes and ketones

    2. Carboxylic Acids
      carboxylic acids - definition

      General formula p 674

      Carboxylic Acid Nomenclature - p 674

      Examples of carboxylic acids p 674

      1. Properties and Uses of Carboxylic Acids

        like inorganic acids these acids lose a hydrogen to water to form a negative ion

        p 674 reaction of carboxylic acid in water

        Usually weaker than inorganic acids. Acetic acid is a carboxylic acid and it is weak. The IUPAC name for acetic acid is ethanoic acid.

        Some of these acids are found in plants and animals e.g. citric acid

        Figure 21-5 p 674 citric acid

        Table 21-5 p 675 Examples of carboxylic acids found in plants and animals.

        Ethanoic and citric acids are used in foods to give them a tart (acidic) flavor.

        Benzoic, propanoic, and sorbic acids are used as preservatives. All three kill microorganisms that cause foods to spoil.

        Most widely used are methanoic and ethanoic acids. Inexpensive to make and so are used as starting materials for chemical processes. e.g. ethanoic acid is used in the production of polyvinyl acetate, PVA, which is used in latex paint, adhesives, and textile coatings.

    3. Esters
      esters - definition

      General formula p 675

      Ester Nomenclature Rules p 675

      Examples of esters p 675

      1. Properties and Uses of Esters

        common in plants and responsible for some distinctive flavors and odors

        Table 21-6 p 676 Common Flavors and Odors Produced by Esters

        At one time they were obtained from natural sources but are now synthesized in the lab.

        Used as food additives

        Figure 21-6 p 676 Structure of isamyl acetate which is found in bananas and is used as an artificial flavoring

      2. Amines
        amines - definition

        General formula p 677

        Usually named using the common system - not the IUPAC system

        Amine Nomenclature p 677

        Examples p 677

        Categorized as primary, secondary, or tertiary, depending on the number of hydrogen atoms of the ammonia molecule that have been replaced.

        Primary amine - definition

        Secondary amine - definition

        Tertiary amine - definition

      3. Properties and Uses of Amines

        chemical properties depend on the electronic structure of the nitrogen atom which has one pair of unshared (nonbonding) electrons. Makes them weak bases in aqueous solutions. The unshared pair of electrons attracts a positive hydrogen atom in a water molecule. e.g. p 677

        Table 21-7 page 679 Classes of Organic Compounds

        Homework 21.2

  3. Organic Reactions
    1. Substitution Reactions

      Substitution reaction - definition

      e.g. halogen + alkane in which the halogen replaces or substitutes for a hydrogen in the alkane

      alkane + halogen ---> alkyl halide + hydrogen halide

      reaction page 682

      Can replace other hydrogens e.g. reacting HF with tetrachloromethane page 682

    2. Addition Reactions

      addition reaction - definition

      One example is the reaction called hydrogenation - a reaction in which one or more hydrogen atoms are added to an unsaturated molecule.

      Vegetable oils contain unsaturated fatty acids, which are long chains of carbon atoms with many double bonds.

      example of hydrogenation reaction page 683

      The reaction does not change the length of the carbon chain, only the number of double bonds (that number is decreased). This change in bonding changes the substance from an oil which is a liquid into a fat which is a solid e.g. vegetable oil into margarine.

    3. Condensation Reactions

      condensation reaction - definition

      When the molecules or parts of a molecule combine water is usually a product of the reaction.

      e.g. page 683 - two amino acids which contain both amine and carboxyl groups; a hydrogen from the amine group of one amino acid combines with the hydroxyl group the carboxyl group of the other amino acid to form a molecule of water; when repeated, this reaction forms a protein.

    4. Elimination Reactions

      elimination reaction - definition

      e.g. page 684 - heating ethanol in the presence of sulfuric acid to produce ethene and water.

      e.g. figure 21-9 - dehydration of sucrose by concentrated sulfuric acid

      Homework 21.3

  4. Polymers

    polymers - definition

    monomers - definition

    can have different or same monomers to form a polymer

    copolymer - definition

    examples in include starch, cellulose, proteins, some plastics and synthetic fibers

    1. Polymer Thermal Properties and Structure

      Polymers are classified by the way they are heated.

      themoplastic polymer - definition

      thermosetting polymer - definition

      Which one is determined by their structure i.e. linear, branched or cross-linked figure 21-10

      Linear polymer - molecules are free to move when heated - they are thermoplastic.

      Branched polymer - have side chains which prevent the molecules fro sliding across each other easily - still likely to be thermoplastic.

      cross-linked polymer - adjacent molecules in the chain have formed bonds and so molecules cannot slide past each other - retain their shape when heated - thermosetting polymers

    2. Addition Polymers

      addition polymer - definition

      e.g. ethene can polymerize with each other to form polyethene (polyethylene) page 686

      the letter n indicates that the reaction can be repeated many times

      1. Forms of Polyethylene and Related Polymers

        Figure 21-11 different forms of polyethylene

        different molecular structures

        HDPE - linear polymer - tends to remain stiff and rigid, used in milk and juice bottles

        LDPE - branched-chain polyethylene - less rigid than HDPE and is used in plastic bags

        cPE - cross link between molecules - tougher and more rigid than HDPE

        Table 21-8 page 687 Additional Polymers

        Polystyrene - a polymer whose properties can be altered

        Pure polystyrene can be melted and molded for use in clear plastic cold drink cups. Can also be made into tiny beads and then soaked in a liquid such as pentane. This causes bubbles to form in the polystyrene and we get polystyrene cups.

        Figure 21-12 page 687 - Two forms of polystyrene

      2. Natural and Synthetic Rubber

        Natural rubber comes from trees. Figure 21-13 page 688.

        Consists of isoprene as the monomer which undergoes an addition reaction to form polyisoprene.

        Natural rubber gets gooey when heated and is dissolved by many solvents such as gasoline.

        1839, Charles Goodyear, added sulfur to molten sulfur made the rubber hard and tough. Process is called vulcanization.

        Vulcanization is a cross-linking process between adjacent polyisoprene molecules that occurs when the molecules are heated with sulfur atoms. Figure 21-14 page 689

        World War II required the development of synthetic rubber since Japan controlled much of the natural rubber trees in the world.

        Styrene-butadiene rubber (SBR) is a copolymer synthetic rubber and is used primarily in tires.

        Another synthetic rubber is neoprene, made from the polymerization of 2-chlorobutadiene which is similar to isoprene except for a chlorine where isoprene has a methyl group - bottom of page 689.

    3. Condensation Polymers
      Condensation polymer - definition

      1. Nylon and Polyamides
        Nylon is a polyamide polymer because it contains the amide group - page 691.

        Polyamides can be knitted or woven into different forms such as stockings and other types of clothing.

        Treating a polyamide with radiation produces extensive cross-linking and the final product is very rigid and strong e.g. Kevlar

      2. Polyester
        Polyethylene terephthalate (PET) is used in tires, food packaging, and bottles. Used to make polyester which is used in some type of clothing. Polyester fabric is made wrinkle resistant by the cross-linking of its polymer strands.

        figure 21-16 - polyester thread

        Homework 21.4

        End of Notes

        Functional Group is an atom or group of atoms that is responsible for specific propertie sof an organic compound.

        Alcohols are organic compounds that contain one or more hydroxyl groups.

        Alkyl halides are organic compounds in which one or more halogen atoms are substituted for one or more hydrogen atoms in a hydrocarbon.

        Ethers are organic compounds in which two hydrocarbon groups are bonded to the same atom of oxygen.

        Aldehydes are organic compounds in which the carbonyl group is attached to a carbon atom at the end of a carbon-atom chain.

        Ketones are organic compounds in which the carbonyl group is attached to carbon atoms within the chain.

        A carbonyl group is a carbon atom with a double bond to an oxygen atom.

        Carboxylic acids are organic compounds that contain the carboxyl functional group.

        A carboxyl group is a carbon atom with a double bond to an oxygen atom and a single bond to a hydroxyl group.

        Esters are organic compounds with carboxylic acid groups in which the hydrogen of the hydroxyl group has been replaced by an alkyl group.

        Amines are organic compounds that can be considered to be derivatives of ammonia, NH3

        A primary amine is one in which one hydrogen atom of an ammonia molecule has been replaced by an alkyl group.

        A secondary amine is one in which two hydrogen atoms of an ammonia molecule have been replaced by alkyl groups.

        A tertiary amine is one in which all three hydogen atoms of an ammonia moelcule have been replaced by alkyl groups.

        A substitution reaction is on ein which one or more atoms replace another atom or group of atoms in a molecule.

        An addition reaction is one in which an atom or molecule is added to an unsaturated molecule and increases the saturation of the molecule.

        A hydrogenation reaction is an addition reaction in which one or more hydrogen atoms are added to an unsatureated molecule.

        A condensation reaction is one in which two molecules o rparts of the same molcule combine.

        An elimination reaction is one in which a simple molecule, such as water or ammonia, is removed from adjacent carbon atoms of a larger molecule.

        Polymers are large molecules made of many small units joined to each other through organic reactions.

        Monomers are small units of polymers.

        Copolymer is a polymer made from two or more different monomers.

        A thermoplastic polymer melts when heated and can be reshaped many times

        A thermosetting polymer does not melt when heated but keeps its original shape.

        An addition polymer is a polymer formed by chain addition reactions between monomers that contain a double bond.

        Vulcanization is a cross-linking process between adjacent polyisoprene molecules that occurs when the molecules are heated with sulfur atoms.

        A condensation polymer is a polymer formed by condensation reactions.