Organic Chemistry Chapter 24

Organic Chemistry Organic chemistry is the chemistry of compounds containing carbon. In this chapter we will discuss the structural features of organic molecules, nomenclature, and a few important chemical reactions.

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

Why is Carbon Unique? 1. Forms four covalent bonds 2. Bonds covalently to: H, O, N, P, S, and all other nonmetals (except noble gases) 3. Carbon atoms join to form: – a. Chains and b. Rings

Common Elements in Organic Compounds

Examples of Organic Chemicals Foods Carbohydrates Fats Proteins Clothing silk, linen, wool, cotton, Dacron, Nylon, Orlon, etc. Plastics Pharmaceuticals Detergents and Soaps Pesticides Gasoline and oils Water purification

Organic vs Inorganic: Differences OrganicInorganic BondingCovalentIonic Physical State (room temp) Gas/liquid common Solids common Melting pointsTend to be lowTend to be very high Sol. In waterTend to be insoluble Much higher percent soluble ConductivityNonconductorsConduct in soln. and molten

Hydrocarbons The simplest organic compounds are hydrocarbons, compounds containing only carbon and hydrogen. The three main groups of hydrocarbons are: saturated hydrocarbons, hydrocarbons with only single bonds between the carbon atoms. unsaturated hydrocarbons, hydrocarbons that contain double or triple bonds between carbon atoms.

Hydrocarbons The simplest organic compounds are hydrocarbons, compounds containing only carbon and hydrogen. The three main groups of hydrocarbons are: aromatic hydrocarbons, hydrocarbons that contain a benzene ring (a six- membered ring of carbon atoms with alternating single and double carbon- carbon bonds described by resonance formulas).

Hydrocarbons The simplest organic compounds are hydrocarbons, compounds containing only carbon and hydrogen. The saturated and unsaturated hydrocarbons are often referred to as the aliphatic hydrocarbons.

Classification of Hydrocarbons

Alkanes Alkanes have the general formula C n H 2n+2 where n = 1,2,3,… only single covalent bonds saturated hydrocarbons because they contain the maximum number of hydrogen atoms that can bond with the number of carbon atoms in the molecule CH 4 C2H6C2H6 C3H8C3H8 methaneethanepropane

Alkanes The alkanes are acyclic, saturated hydrocarbons that form a homologous series of compounds, with the general formula C n H 2n+2. The simplest hydrocarbon is methane, CH 4. molecular formula structural formula

Alkanes The structural formulas for the first four straight-chain (or normal) alkanes are shown below. methaneethanepropanebutane

Alkanes Chemists often use condensed structural formulas, where the bonds around each carbon atom are not explicitly written. methaneethanepropanebutane

Alkanes The alkanes constitute a homologous series of compounds in which one compound differs from a preceding one by a fixed group of atoms, in this case, a –CH 2 – group. Members of a homologous series have similar chemical properties, and their physical properties change throughout the series in a regular way.

Hydrocarbons: They are nonpolar molecules and consequently are not soluble in water but are soluble in typical nonpolar organic solvents like toluene or pentane.

Alkanes The alkanes constitute a homologous series of compounds in which one compound differs from a preceding one by a fixed group of atoms, in this case, a –CH 2 – group. Note that the melting and boiling points increase with an increase in the number of carbon atoms.

Constitutional Isomerism and Branched-Chain Alkanes In addition to straight-chain alkanes, branched-chain alkanes are possible. For example, isobutane (or 2- methylpropane) has the structure or

Constitutional Isomerism and Branched-Chain Alkanes In addition to straight-chain alkanes, branched-chain alkanes are possible. Note that isobutane, C 4 H 10, has the same molecular formula as normal butane. Butane and isobutane are constitutional (or structural) isomers, compounds with the same molecular formula but different structural formulas.

Models of isobutane and butane.

Structural isomers are molecules that have the same molecular formula but different structures

How many structural isomers does pentane, C 5 H 12, have? CCCC C HHHHH H HHHHH H CCC C HCH 3 HH H HHHH H CC C H H H HH H n-pentane 2-methylbutane 2,2-dimethylpropane

Cycloalkanes The cycloalkanes are cyclic, saturated hydrocarbons that form another homologous series with the general formula C n H 2n in which the carbon atoms are joined in a ring. Below is the structure for cyclobutane.

Cycloalkanes The cycloalkanes are cyclic, saturated hydrocarbons that form another homologous series with the general formula C n H 2n in which the carbon atoms are joined in a ring.

Alkane Nomenclature 1.The parent name of the hydrocarbon is that given to the longest continuous chain of carbon atoms in the molecule. CH 3 CH 2 CHCH 2 CH methylheptane 2.An alkane less one hydrogen atom is an alkyl group. CH 4 CH 3 methane methyl

Alkane Nomenclature

3.When one or more hydrogen atoms are replaced by other groups, the name of the compound must indicate the locations of carbon atoms where replacements are made. Number in the direction that gives the smaller numbers for the locations of the branches. CH 3 CHCH 2 CH methylpentane CH 3 CH 2 CHCH methylpentane

Alkane Nomenclature 4.Use prefixes di-, tri-, tetra-, when there is more than one alkyl branch of the same kind. CH 3 CH CH 2 CH ,3-dimethylhexane CH 3 CHCCH 2 CH ,3-dimethylhexane

Alkane Nomenclature 5.Use previous rules for other types of substituents. When there are two or more different branches, the name of each branch, with its position number, precedes the base name. The branch names are placed in alphabetical order. CH 3 CH CH 3 Br 1234 NO 2 2-bromo-3-nitrobutane CH 2 CHCH 3 Br 1234 NO 2 1-bromo-3-nitrobutane

What is the IUPAC name of the following compound? CH 3 CHCH 2 CHCH 2 CH 3 C2H5C2H5 CH 2 CH 3 2-methyl-4-ethyloctane What is the structure of 2-propyl-4-methylhexane? CH 3 CHCH 2 CHCH 2 CH 3 C2H5C2H5

Reactions of Alkanes With Oxygen All hydrocarbons burn in an excess of O 2 to produce carbon dioxide, water, and heat. For example, a propane gas grill uses the reaction

Substitution Reactions of Alkanes A substitution reaction is a reaction in which a part of the reacting molecule is substituted for an H atom on a hydrocarbon. For example, the reaction of ethane with Cl 2. Cl-Cl + H-Cl +

Alkane Reactions CH 4 (g) + 2O 2 (g) CO 2 (g) + 2H 2 O (l)  H 0 = kJ Combustion Halogenation CH 4 (g) + Cl 2 (g) CH 3 Cl (g) + HCl (g) light Cl 2 + energy Cl + Cl Cl + CH H H H CH H H + HCl CH H H + Cl Cl CCl H H H + Cl

Cycloalkanes Alkanes whose carbon atoms are joined in rings are called cycloalkanes. They have the general formula C n H 2n where n = 3,4,…

Cycloalkanes

Alkenes and Alkynes The alkenes and alkynes are unsaturated hydrocarbons (cyclic or acyclic) that contain carbon-carbon double or triple bonds. Under proper conditions, molecular hydrogen can be added to an alkene or an alkyne to produce a saturated compound in a process called catalytic hydrogenation.

Alkenes and Geometric Isomers Alkenes are hydrocarbons with the general formula C n H 2n and contain a carbon-carbon double bond. (also called olefins) The simplest alkene is ethylene.

Alkenes and Geometric Isomers Alkenes are hydrocarbons with the general formula C n H 2n and contain a carbon-carbon double bond. (also called olefins) Geometric isomers are isomers in which some atoms occupy different relative positions in space.

achiralchiral

Alkenes and Geometric Isomers Alkenes are hydrocarbons with the general formula C n H 2n and contain a carbon-carbon double bond. (also called olefins) For example, 2-butene has two geometric isomers, called cis-2-butene and trans-2- butene. cis-2-butenetrans-2-butene

Alkenes Alkenes have the general formula C n H 2n where n = 2,3,… contain at least one carbon-carbon double bond also called olefins CH 2 CHCH 2 CH 3 1-butene CH 3 CH CH 3 2-butene CC Cl HH CC H H cis-dichloroethylenetrans-dichloroethylene

Cis-Trans Isomerization in the Vision Process

Oxidation Reactions of Alkenes Because alkenes are hydrocarbons, they undergo complete combustion reactions with oxygen. Unsaturated hydrocarbons can also be partially oxidized under relatively mild conditions. For example, when aqueous potassium permanganate is added to an alkene (or alkyne), the purple color of KMnO 4 fades as a brown precipitate of MnO 2 forms.

Test for unsaturation using KMnO 4 (aq) solution.

Addition Reactions of Alkenes Alkenes are more reactive than alkanes because many reactants add to the double bond. An addition reaction is a reaction in which parts of a reactant are added to each carbon atom of a carbon-carbon double bond which converts to a carbon-carbon single bond.

Addition Reactions of Alkenes Alkenes are more reactive than alkanes because many reactants add to the double bond. A simple example is the addition of a halogen, such as Br 2, to propene. + Br 2

Alkene Reactions Cracking Addition Reactions CH 2 CH 2 (g) + HBr (g) CH 3 CH 2 Br (g) CH 2 CH 2 (g) + Br 2 (g) CH 2 Br CH 2 Br (g) C 2 H 6 (g) CH 2 CH 2 (g) + H 2 (g) Pt catalyst

Alkynes Alkynes are unsaturated hydrocarbons containing a carbon-carbon triple bond. The general formula is C n H 2n-2. The simplest alkyne is acetylene (ethyne).

Alkynes Alkynes have the general formula C n H 2n-2 where n = 2,3,4,… contain at least one carbon-carbon triple bond 1-butyne2-butyne CH CCH 2 CH 3 CC Production of acetylene CaC 2 (s) + 2H 2 O (l) C 2 H 2 (g) + Ca(OH) 2 (aq)

Alkyne Reactions Addition Reactions Hydrogenation CH CH (g) + H 2 (g) CH 2 CH 2 (g) CH CH (g) + HBr (g) CH 2 CHBr (g) CH CH (g) + Br 2 (g) CHBr CHBr (g) CH CH (g) + 2Br 2 (g) CHBr 2 CHBr 2 (g)

Nomenclature of Alkenes and Alkynes The following four IUPAC rules are applied in naming the branched-chain alkenes and alkynes. The rules are essentially the same as those for alkanes, except that names end in –ene for alkenes and –yne for alkynes. The position of the double (or triple) bond is indicated in the name by bond position number.

Nomenclature of Alkenes and Alkynes The following four IUPAC rules are applied in naming the branched-chain alkenes and alkynes. 3-methyl-1-pentene

Nomenclature of Alkenes and Alkynes The following four IUPAC rules are applied in naming the branched-chain alkenes and alkynes. Recall that alkenes also exhibit cis and trans isomerism and so either cis or trans must be included in the name.

Aromatic Hydrocarbons Aromatic hydrocarbons usually contain benzene rings-six membered rings of carbon atoms with alternating C-C single and C=C double bonds. The structure of benzene is

Aromatic Hydrocarbons Aromatic hydrocarbons usually contain benzene rings-six membered rings of carbon atoms with alternating C-C single and C=C double bonds.. Aromatic compounds are found everywhere from pain relievers to flavoring agents.

Aromatic Hydrocarbons C C C CC C H H H H H H C C C CC C H H H H H H

Aromatic Compound Nomenclature CH 2 CH 3 ethylbenzene Cl chlorobenzene NH 2 aminobenzene NO 2 nitrobenzene Br 1,2-dibromobenzene Br 1,3-dibromobenzene

Aromatic Compound Reactions H H H H H H Br H H H H H + HBr+ Br 2 FeBr 3 catalyst H H H H H H CH 2 CH 3 H H H H H + HCl+ CH 3 CH 2 Cl AlCl 3 catalyst Substitution reaction

Polycyclic Aromatic Hydrocarbons

Derivatives of Hydrocarbons A functional group is a reactive portion of a molecule that undergoes predictable reactions. In the previous sections we discussed the hydrocarbons and their reactions. All other organic compounds can be considered to be derivatives of hydrocarbons.

Organic Compounds Containing Oxygen Many of the important functional groups in organic compounds contain oxygen. Examples are alcohols ethers aldehydes ketones carboxylic acids esters

Organic Compounds Containing Oxygen An alcohol is a compound obtained by substituting a hydroxyl group (-OH) for an –H atom on a carbon atom of a hydrocarbon group. Some examples are methanolethanol2-propanol

Functional Group Chemistry Alcohols contain the hydroxyl functional group and have the general formula R-OH.

C 6 H 12 O 6 (aq) 2CH 3 CH 2 OH (aq) + 2CO 2 (g) enzyme CH 2 CH 2 (g) + H 2 O (g) CH 3 CH 2 OH (g) H 2 SO 4 Biological production of ethanol Commercial production of ethanol Metabolic oxidation of ethanol CH 3 CH 2 OH CH 3 CHO + H 2 alcohol dehydrogenase

Organic Compounds Containing Oxygen An ether is a compound with an oxygen “bridge” between two alkyl groups. An example is diethyl ether This is the most common ether, often called simply ether, used as an anesthetic.

Functional Group Chemistry Ethers have the general formula R-O-R’. CH 3 OH + HOCH 3 CH 3 OCH 3 + H 2 O H 2 SO 4 catalyst Condensation Reaction

Organic Compounds Containing Oxygen An aldehyde is a compound containing a carbonyl group with at least one H atom attached to it. An example is ethanal

Organic Compounds Containing Oxygen A ketone is a compound containing a carbonyl group with two hydrocarbon groups attached to it. An example is 2-butanone

Functional Group Chemistry Aldehydes and ketones contain the carbonyl ( ) functional group. O C R C H O aldehydes have the general formulaR C R’ O ketones have the general formulaH C H O H C O CH 3 C O H3CH3C formaldehydeacetaldehydeacetone

Organic Compounds Containing Oxygen A carboxylic acid is a compound containing the carboxyl group, -COOH. An example is ethanoic acid

Functional Group Chemistry Carboxylic acids contain the carboxyl ( -COOH ) functional group.

Organic Compounds Containing Oxygen An ester is a compound formed from a carboxylic acid, RCOOH, and an alcohol, R’OH. The general structure is

Functional Group Chemistry Esters have the general formula R’COOR, where R is a hydrocarbon group. CH 3 COOH + HOCH 2 CH 3 CH 3 C O CH 2 CH 3 + H 2 O O ethyl acetate

Organic Compounds Containing Nitrogen Most organic bases are amines, which are compounds that are structurally derived by replacing one or more hydrogen atoms of ammonia with hydrocarbon groups. primary aminesecondary aminetertiary amine

Functional Group Chemistry Amines are organic bases with the general formula R 3 N. CH 3 NH 2 + H 2 O RNH OH - CH 3 CH 2 NH 2 + HCl CH 3 CH 2 NH 3 + Cl -

Organic Compounds Containing Nitrogen Most organic bases are amines, which are compounds that are structurally derived by replacing one or more hydrogen atoms of ammonia with hydrocarbon groups.

Organic Compounds Containing Nitrogen Amides are compounds derived from the reaction of ammonia, or of a primary or secondary amine, with a carboxylic acid. The general formula for a common amide is

Sources and Uses of Alkanes and Cycloalkanes Fossil fuels are the principal source of all types of organic compounds. Crude oil is a mixture of alkanes, cycloalkanes, and aromatic hydrocarbons.

Sources and Uses of Alkanes and Cycloalkanes Fossil fuels are the principal source of all types of organic compounds. Because fossil fuels are mixtures of hydrocarbons, it is usually necessary to separate these mixtures by distillation.

Chemistry In Action: The Petroleum Industry Crude Oil

Sources and Uses of Alkanes and Cycloalkanes The alkanes serve as the starting point for most plastics and pharmaceuticals.

Class Exercises Organic Functional Groups Chart Organic Nomenclature I Organic Nomenclature II Drawing organic structures

WORKED EXAMPLES

Worked Example 24.1

Worked Example 24.3

Worked Example 24.5