Unit 12: Organic Chemistry

Unit 12: Organic Chemistry Chapter 22-24 General Chemistry 1 Edmond North High School

Organic Chemistry • Organic chemistry is the chemistry of compounds containing carbon. • Carbon has the ability to form long chains. • Without this property, large biomolecules such as proteins, lipids, carbohydrates, and nucleic acids could not form.

The Bonding of Carbon • Because carbon has four valence electrons, it can form four covalent bonds. • Carbon forms single, double, and triple bonds to achieve a filled octet. • A unique feature of carbon is its ability to bond with other carbons to form long chains or rings of various length.

Saturated Hydrocarbons • A hydrocarbon in which all the carbon atoms are connected to each other by single bonds is called a saturated hydrocarbon. • Another name for a saturated hydrocarbon is an alkane. • Although burning alkanes for fuel is their most common use, they are also used as solvents in paint removers, glues, and other products. • Alkanes are the simplest hydrocarbons.

Alkanes • The carbons in an alkane can be arranged in a chain or a ring, and both chains and rings can have branches of other carbon chains attached to them. • This means they are hydrocarbon chains where all the bonds between carbons are single bonds. • Alkanes that have no branches are called straight-chain alkanes.

Alkanes • The structural formulas for the first four straight-chain (or normal) alkanes are shown below. methane ethane propane butane

Alkanes • Some alkanes have a branched structure. • In these compounds, a chain of one or more carbons is attached to a carbon in the longest continuous chain, which is called the parent chain.

Alkanes • The carbon atoms in alkanes can also link up to form closed rings. The most common rings contain five or six carbons. • The structures of these compounds can be drawn showing all carbon and hydrogen atoms.

Alkanes • Structural diagrams can be simplified by using straight lines to represent the bonds between atoms in the rings. • In these ring diagrams, each corner represents a carbon atom.

Alkanes • Structural diagrams of straight- and branched-chain hydrocarbons also can be written in a simplified way by leaving out some of the bonds. • For example, the formula for propane can be written as CH3—CH2—CH3. • In this type of shorthand structure, the bonds between C and H are understood. • In an even more simplified type of shorthand, the condensed structural formula for propane can be written as CH3CH2CH3. • Here, the bonds both between C and C and between C and H are understood.

Naming Alkanes • To name a branched alkane, you must be able to answer three questions about its structure. • How many carbons are in the longest continuous chain of the molecule? • How many branches are on the longest chain and what is their size? • To which carbons in the longest chain are the branches attached? • For convenience, the carbon atoms in organic compounds are given position numbers. • In straight-chain hydrocarbons, the numbering can begin at either end. It makes no difference. • In branched hydrocarbons, the numbering begins at the end closest to the branch.

Naming Alkanes • Name the compound pictured. • Four carbons are in the longest continuous chain, so butane is the parent chain and will be part of the compound’s name. • There is only one branch, and it contains one carbon. • Instead of calling this a methane branch, change the -ane in methane to -yl. Thus, this is a methyl branch. • Because the methyl branch is attached to the second carbon of the butane chain, this compound has the name 2-methylbutane.

Isomers • Compounds that have the same formula but different structures are called isomers. • Butane and 2-methylpropane are known as structural isomers. • Each has the molecular formula C4H10, but they have different structural formulas because the carbon chains have different shapes.

Properties of Alkanes • Properties are affected by the structure or arrangement of atoms present in a molecule. • Another factor that affects properties of alkanes is chain length. • In general, the more carbons present in a straight-chain alkane, the higher its melting and boiling points. • A property shared by all alkanes is their relative unreactivity. • Because alkanes don’t have any polar bonds, they undergo only a small number of reactions and will dissolve only those organic compounds that are nonpolar or that have low polarity, such as oils and waxes.

Cycloalkanes • The cycloalkanes are ringed, saturated hydrocarbons. • Five- and six-membered rings are most stable.

Unsaturated Hydrocarbons • A hydrocarbon that has one or more double or triple bonds between carbons is called an unsaturated hydrocarbon. • In saturated hydrocarbons, carbon atoms share only one pair, whereas in unsaturated hydrocarbons, the carbon atoms participating in double or triple bonds share two or three pairs.

Alkenes • A hydrocarbon in which one or more double bonds link carbon atoms together is called an alkene. • Alkenes are named using the root names of the alkanes, with the -ane ending changed to -ene.

Naming Alkenes • Use the following steps in naming alkenes. • Count the number of carbons in the longest continuous chain that contains the double bond, and assign the appropriate alkene name. • Number the carbons consecutively in the longest chain, starting at the end of the chain that will result in the lowest possible number for the first carbon to which the double bond is attached. • Write the number corresponding to the first carbon in the double bond, followed by a hyphen and then the alkene name. • Name: CH2 = CHCH2CH3

Alkenes • Double bonds prevent the carbons from rotating. • If two different groups are attached to the carbons, the alkene can have two different structures called geometric isomers. • In a cis- isomer, the similar groups are on the same side of the double bond. • In a trans- isomer, the similar groups are on opposite sides of the double bond.

Alkynes • Another type of unsaturated hydrocarbon, called an alkyne, contains a triple bond between two carbon atoms.

Nomenclature of Alkynes 4-methyl-2-pentyne • Analogous to naming of alkenes. • Suffix is -yne rather than –ene.

Aromatic Hydrocarbons • Another group of unsaturated hydrocarbons has distinctive, six-carbon ring structures and are called aromatic hydrocarbons. • The simplest compound in this group is benzene, with the molecular formula C6H6. • Benzene contains six carbons joined together in a flat ring. • Aromatic hydrocarbons were originally named because most of them have distinctive aromas.

Benzene • Aromatic hydrocarbons usually contain benzene rings-six membered rings of carbon atoms with alternating C-C single and C=C double bonds. • In this hexagon, each corner represents a carbon atom. • The circle in the middle of the structure represents the cloud of six electrons that are shared equally by the six carbon atoms in the molecule.

Aromatic Nomenclature • Many aromatic hydrocarbons are known by their common names.

Substituted Hydrocarbons • Substituted hydrocarbons have a structure the same as hydrocarbons except for the substitution of atoms of another element for part of the hydrocarbons. • The part of a molecule having a specific arrangement of atoms that is largely responsible for the chemical behavior of the parent molecule is called a functional group. • Functional groups can be atoms, groups of atoms, or bond arrangements.

Functional Groups • Carbon atoms can also form strong covalent bonds with other elements, the most common of which are oxygen, nitrogen, fluorine, chlorine, bromine, iodine, sulfur, and phosphorus. • Atoms of these elements occur in organic substances as parts of functional groups. • A functional group in an organic molecule is an atom or group of atoms that always reacts in a certain way. • The addition of a functional group to a hydrocarbon structure always produces a substance with physical and chemical properties that differ from those of the parent hydrocarbon.

Functional Groups • The symbols R and R′ represent any carbon chains or rings bonded to the functional group. • And * represents a hydrogen atom, carbon chain, or carbon ring.

Organic Compounds and Their Functional Groups • The simplest functional groups can be thought of as substituent groups attached to a hydrocarbon. • The elements in group 7A of the periodic table—fluorine, chlorine, bromine, and iodine—are the halogens. • Any organic compound that contains a halogen substituent is called a halocarbon. • If you replace any of the hydrogen atoms in an alkane with a halogen atom, you form an alkyl halide.

Organic Compounds Containing Halogens • An aryl halide is an organic compound containing a halogen atom bonded to a benzene ring or other aromatic group. • The structural formula for an aryl halide is created by first drawing the aromatic structure and then replacing its hydrogen atoms with the halogen atoms specified.

Alcohols • An oxygen-hydrogen group covalently bonded to a carbon atom is called a hydroxyl group (—OH). • An organic compound in which a hydroxyl group replaces a hydrogen atom of a hydrocarbon is called an alcohol. • The general formula for an alcohol is ROH. • Alcohols are named from parent hydrocarbon; suffix changed to -oland number designates carbon to which hydroxyl is attached. • Alcohols are more acidic than other hydrocarbons.

Ethers • An ether is an organic compound containing an oxygen atom bonded to two carbon atoms. • Ethers have the general formula ROR′. • The simplest ether is one in which oxygen is bonded to two methyl groups. • Note the relationship between methanol and methyl ether in the following diagram. • Tend to be quite unreactive. • Therefore, they are good polar solvents. • Found in many fruits and perfumes

Amines • Another class of organic compounds contains nitrogen. • Amines contain nitrogen atoms bonded to carbon atoms in aliphatic chains or aromatic rings and have the general formula RNH2. • Generally have strong, unpleasant odors.

The Carbonyl Group • The arrangement in which an oxygen atom is double-bonded to a carbon atom is called a carbonyl group. • This group, which can be represented as shown below, is the functional group in organic compounds known as aldehydes and ketones.

Aldehydes • An aldehyde is an organic compound in which a carbonyl group located at the end of a carbon chain is bonded to a carbon atom on one side and a hydrogen atom on the other. • Aldehydes have the general formula *CHO, where * represents an alkyl group or a hydrogen atom.

Ketones • A carbonyl group also can be located within a carbon chain rather than at the end. • A ketone is an organic compound in which the carbon of the carbonyl group is bonded to two other carbon atoms. • Ketones have the general formula shown to the right.

Carboxylic Acids • A carboxylic acid is an organic compound that has a carboxyl group. • A carboxyl group consists of a carbonyl group bonded to a hydroxyl group. • Thus, carboxylic acids have the general formula shown to the right. • Tart tasting. • Carboxylic acids are weak acids.

Organic Compounds Derived From Carboxylic Acids • Several classes of organic compounds have structures in which the hydrogen or the hydroxyl group of a carboxylic acid is replaced by a different atom or group of atoms. • The two most common classes are esters and amides.

Ester • An ester is any organic compound with a carboxyl group in which the hydrogen of the hydroxyl group has been replaced by an alkyl group, producing the following arrangement.

Amides • An amide is an organic compound in which the —OH group of a carboxylic acid is replaced by a nitrogen atom bonded to other atoms. • The general structure of an amide is shown to the right.

Monomers and Polymers • A large molecule that is made up of many smaller, repeating units is called a polymer. • A polymer forms when hundreds or thousands of these small individual units, which are called monomers, bond together in chains. • The monomers that bond together to form a polymer may all be alike, or they may be different.

Polymers • A reaction in which the monomer units are bonded together to from a polymer is called a polymerization reaction. • The repeating group of atoms in the monomer is called the structural unit of the polymer. • The letter n is used to represent the number of structural units. • The properties of a polymer are different from those of the monomers that formed it.

Rubber • Another process that often occurs in combination with addition or condensation reactions is the linking together of many polymer chains. • This is called cross-linking, and it gives additional strength to a polymer. • In 1844, Charles Goodyear discovered that heating the latex from rubber trees with sulfur can cross-link the hydrocarbon chains in the liquid latex. • The solid rubber that is formed can be used in tires and rubber balls.

Addition Reactions • In an addition reaction, monomers that contain double bonds add onto each other, one after another, to form long chains. • The product of an addition polymerization reaction contains all of the atoms of the starting monomers.

Condensation Reactions • Many times two organic reactants form a larger organic product, such as the aspirin. • This type of reaction is known as a condensation reaction. • In a condensation reaction, two smaller organic molecules combine to form a more complex molecule, accompanied by the loss of a small molecule such as water. • Typically, the molecule lost is formed from one particle from each of the reactant molecules.

Elimination Reactions • The formation of alkenes from alkanes is an elimination reaction, a reaction in which a combination of atoms is removed from two adjacent carbon atoms forming an additional bond between the carbon atoms. • The atoms that are eliminated usually form stable molecules, such as H2O, HCl, or H2.

Oxidation-Reduction Reactions • Many organic compounds can be converted to other compounds by oxidation and reduction reactions. • For example, suppose that you wish to convert methane, the main constituent of natural gas, to methanol, a common industrial solvent and raw material for making formaldehyde and methyl esters.

Molecules of Life • Many of the most important molecules in your body are polymers. • Proteins, carbohydrates, and nucleic acids, all extremely large molecules, are formed from small monomer subunits. • Although lipids are usually not considered to be polymers, they, too, are formed from smaller molecules that have been linked together. • Complex reactions in your cells use some of these molecules and a few others to make a fourth group of biomolecules, the nucleic acids. • The study of the chemistry of living things is called biochemistry.

Proteins • A protein is an organic polymer composed of amino acids bonded together in one or more chains. • An amino acid has a central carbon atom, to which are bonded a carboxyl group, an amino group, a hydrogen atom, and a variable side chain designated as R. • Amino acids bond to each other by forming a peptide bond, an amide group formed by a condensation reaction between the carboxyl group of one amino acid and the amino group of another.

Enzymes • This folding produces surface features responsible for the protein’s function. • An enzyme is a function-specific protein that has an active site in order to catalyze biological reactions. • The reactants in an enzyme-catalyzed process are called substrates. • The substrate(s) bind to the enzyme at a location called the enzyme’s active site.

Carbohydrates • Familiar carbohydrates include sugars, starches, and cellulose. • Simple carbohydrates consist of a chain of carbon atoms having hydroxyl (–OH) groups and a carbonyl group, often in the form of an aldehyde group.

Unit 12: Organic Chemistry