© 2013 Pearson Education, Inc. Outline 12.1The Nature of Organic Molecules 12.2Families of Organic...

© 2013 Pearson Education, Inc.

Outline

12.1 The Nature of Organic Molecules

12.2 Families of Organic Molecules: Functional Groups

12.3 The Structure of Organic Molecules: Alkanes and Their Isomers

12.4 Drawing Organic Structures

12.5 The Shapes of Organic Molecules

12.6 Naming Alkanes

12.7 Properties of Alkanes

12.8 Reactions of Alkanes

12.9 Cycloalkanes

12.10 Drawing and Naming Cycloalkanes


Goals1. What are the basic properties of organic compounds?

Be able to identify organic compounds and the types of bonds contained in them.

2. What are functional groups, and how are they used to classify organic molecules? Be able to classify organic molecules into families by functional group.

3. What are isomers? Be able to recognize and draw constitutional isomers.

4. How are organic molecules drawn?

Be able to convert between structural formulas and condensed or line structures.

5. What are alkanes and cycloalkanes, and how are they named?

Be able to name an alkane or cycloalkane from its structure, or write the structure, given the name.

• What are the general properties and chemical reactions of alkanes?

Be able to describe the physical properties of alkanes and the products formed in the combustion and halogenation reactions of alkanes



• Organic chemistry is the study of carbon compounds.

• Carbon is tetravalent; it always forms four bonds.

• Organic molecules have covalent bonds.



• When carbon bonds to a more electronegative element, polar covalent bonds result.

• Organic molecules have specific three-dimensional shapes.

Chloromethane, CH3Cl



• Organic molecules often contain nitrogen and oxygen in addition to carbon and hydrogen.– Nitrogen can form single, double, and triple bonds to

carbon.– Oxygen can form single and double bonds.– Hydrogen can only form single bonds to carbon.

• Covalent bonding– Individual molecules– Lower melting and boiling points than inorganic salts– Many organic compounds are liquids or low melting

solids at room temperature, and a few are gases.



• Most organic compounds are insoluble in water.

• Almost all of those that are soluble do not conduct electricity.

• Only small polar organic molecules or large molecules with many polar groups interact with water molecules and thus, dissolve in water.

• Lack of water solubility for organic compounds has important consequences.

• The interior of a living cell is a water solution that contains many hundreds of different compounds. Cells use membranes composed of water-insoluble organic molecules to enclose their interiors and to regulate the flow of substances across the cell boundary.



• Organic compounds can be classified into families according to structural features.

• The chemical behavior of family members is often predictable based on their specific grouping of atoms.

• There are a few general families of organic compounds whose chemistry falls into simple patterns.

• The structural features that allow classification of organic compounds into families are called functional groups.



• A Functional group is an atom or group of atoms within a molecule that has a characteristic physical and chemical behavior.

• Each functional group is part of a larger molecule, and a molecule may have more than one class of functional group present.

• A given functional group tends to undergo the same reactions in every molecule that contains it.

• The chemistry of an organic molecule is primarily determined by the functional groups it contains, not by its size or complexity.



Continued



• The first four families are hydrocarbons, organic compounds that contain only carbon and hydrogen.

– Alkanes have only single bonds and contain no functional groups.

– Alkenes contain a carbon–carbon double-bond functional group.

– Alkynes contain a carbon–carbon triple-bond functional group.

– Aromatic compounds contain a six-membered ring of carbon atoms with three alternating double bonds.



• The next four families have functional groups that contain only single bonds and a carbon atom bonded to an electronegative atom.

– Alkyl halides have a carbon–halogen bond.

– Alcohols have a carbon–oxygen bond.

– Ethers have two carbons bonded to the same oxygen.

– Amines have a carbon–nitrogen bond.

• The next six families contain a carbon–oxygen double bond: aldehydes, ketones, carboxylic acids, anhydrides, esters, and amides.

• The remaining three families have functional groups that contain sulfur: thioalcohols (known simply as thiols), sulfides, and disulfides. These play an important role in protein function.



• The general rule for all hydrocarbons except methane is that each carbon must be bonded to at least one other carbon.

• The carbon atoms bond together to form the “backbone” of the compound, with the hydrogens on the periphery.

• The general formula for alkanes is CnHn+2 where n is the number of carbons in the compound.

• As larger numbers of carbons and hydrogens combine, the ability to form isomers arises.

• Compounds that have the same molecular formula but different structural formulas are called isomers.



• There are two ways in which molecules that have the formula C4H10 can be formed.



• A straight-chain alkane is an alkane that has all its carbons connected in a row.

• A branched-chain alkane is an alkane that has a branching connection of carbons.

• Constitutional isomers are compounds with the same molecular formula, but with different connections among their atoms.

• Constitutional isomers of a given molecular formula are chemically distinct from one another. They have different structures and physical properties.



• When the molecular formula contains atoms other than carbon and hydrogen, the constitutional isomers obtained can also be functional group isomers.

• These are isomers that differ in both molecular connection and family classification.

• Ethyl alcohol and dimethyl ether both have the formula C2H6O, but have very different properties.



• A condensed structure is a shorthand way of drawing structures in which C–C and C–H bonds are understood rather than shown.



• Occasionally, not all the CH2 groups (called methylenes) are shown.

• CH2 is shown once in parentheses, with a subscript indicating the number of methylene units strung together.

CH3CH2CH2CH2CH2CH3 = CH3(CH2)4CH3



• A line structure (or line-angle structure) is a shorthand way of drawing structures in which carbon and hydrogen atoms are not shown. – A carbon is understood to be wherever a line begins or

ends and at every intersection of two lines.– Hydrogens are understood to be wherever they are

needed to have each carbon form four bonds.



1. Each carbon–carbon bond is represented by a line.

2. Anywhere a line ends or begins, as well as any vertex where two lines meet, represents a carbon atom.

3. Any atom, other than another carbon or a hydrogen, attached to a carbon must be shown.

4. Since a neutral carbon atom forms four bonds, all bonds not shown for any carbon are understood to be the number of carbon–hydrogen bonds needed to have the carbon form four bonds.



• Every carbon atom in an alkane has its four bonds pointing toward the four corners of a tetrahedron.

• The two parts of a molecule joined by a carbon–carbon single bond in a noncyclic structure are free to spin around the bond, giving rise to an infinite number of possible conformations.

• The various conformations of a molecule are called conformers.



• At any given instant, most of the molecules have the least crowded, lowest-energy extended conformation.

• As long as two structures have identical connections between atoms, and are interconvertable, they are conformers.


12.6 Naming Alkanes

• The system of naming (nomenclature) was devised by the International Union of Pure and Applied Chemistry, IUPAC.

• In the IUPAC system for organic compounds, a chemical name has three parts: prefix, parent, and suffix.

– The prefix specifies the location of functional groups and other substituents.

– The parent tells how many carbon atoms are present in the longest continuous chain.

– The suffix identifies to which family the molecule belongs.


12.6 Naming Alkanes

• Straight-chain alkanes are named by counting the number of carbon atoms and adding the family suffix -ane.

• Straight-chain alkanes have no substituents, so prefixes are not needed.


12.6 Naming Alkanes


12.6 Naming Alkanes

• Substituents such as —CH3 and —CH2CH3, that branch off the main chain are called alkyl groups.– Methyl group: —CH3

– Ethyl group: —CH2CH3


12.6 Naming Alkanes

• The situation is more complex for larger alkanes.


12.6 Naming Alkanes

• There are four possible substitution patterns for carbons attached to four atoms.– A primary (1°) carbon atom is a carbon atom

with 1 other carbon attached to it.– A secondary (2°) carbon atom is a carbon

atom with 2 other carbons attached to it.– A tertiary (3°) carbon atom is a carbon atom

with 3 other carbons attached to it.– A quaternary (4°) carbon atom is a carbon

atom with 4 other carbons attached to it.


12.6 Naming AlkanesBranched-chain alkanes can be named by following four steps:

1. Name the main chain. Find the longest continuous chain of carbons, and name the chain according to the number of carbon atoms it contains. The longest chain may not be immediately obvious.

2. Number the carbon atoms in the main chain, beginning at the end nearer the first branch point.

3. Identify the branching substituents, and number each according to its point of attachment to the main chain.

4. Write the name as a single word, using hyphens to separate the numbers from the different prefixes and commas to separate numbers if necessary. If two or more different substituent groups are present, cite them in alphabetical order. If two or more identical substituents are present, use one of the prefixes di-, tri-, tetra-, and so forth, but do not use these prefixes for alphabetizing purposes.



• Alkanes contain only nonpolar C–C and C–H bonds. The only intermolecular forces influencing them are weak London dispersion forces.

• The effect of these forces is shown in the regularity with which the melting and boiling points of straight-chain alkanes increase with molecular size. – The first four alkanes, methane, ethane, propane, and

butane, are gases at room temperature and pressure. – Alkanes with 5–15 carbon atoms are liquids.– Alkanes with 16 or more carbon atoms are generally

low-melting, waxy solids.



• Alkanes are insoluble in water but soluble in nonpolar organic solvents.

• Because alkanes are generally less dense than water, they float on its surface.

• Low-molecular-weight alkanes are volatile and must be handled with care because their vapors are flammable.

• Mixtures of alkane vapors and air can explode when ignited by a single spark.

• Mineral oil, petroleum jelly, and paraffin wax are mixtures of higher alkanes. All are harmless to body tissue and are used in numerous food and medical applications.



Properties of Alkanes

• Odorless or mild odor, colorless, tasteless, nontoxic

• Nonpolar, insoluble in water but soluble in nonpolar organic solvents, less dense than water

• Flammable, otherwise not very reactive



Organic Chemistry and the Curved Arrow Formalism• Organic chemists look at how and why reactions occur by

examining the flow of electrons. • Chemists use what is loosely known as “electron pushing” and

have adopted what is known as curved arrow formalism to represent it.

• The movement of electrons is depicted using curved arrows, where the number of electrons corresponds to the head of the arrow. Single-headed arrows represent movement of one electron, while a double-headed arrow indicates the movement of two electrons.

• The convention is to show the movement from an area of high electron density (the start of the arrow) to one of lower electron density (the head of the arrow).

• It is important to get used to thinking of reactions as an “electron flow.”



Combustion• The reaction of an alkane with oxygen is called

combustion, an oxidation reaction that commonly takes place in a controlled manner in an engine or furnace.

• Carbon dioxide and water are the products of complete combustion of any hydrocarbon, and a large amount of heat is released.

• When hydrocarbon combustion is incomplete, carbon monoxide and carbon-containing soot are among the products.



Combustion (Continued)• Carbon monoxide is a highly toxic and

dangerous substance, especially because it has no odor and can easily go undetected.

• Breathing air that contains as little as 2% CO for only one hour can cause respiratory and nervous system damage or death.

• The supply of oxygen to the brain is cut off by carbon monoxide because it binds strongly to hemoglobin where oxygen is normally bound.

• CO2 is nontoxic and causes no harm, except by suffocation when present in high concentration.



Halogenation• Halogenation is the replacement of an alkane hydrogen

by a chlorine or bromine initiated by heat or light. • Halogenation is used to prepare a number of key

industrial solvents, as well as other molecules that are used for the preparation of other larger organic molecules.

• In a halogenation reaction, only one H at a time is replaced. If allowed to react for a long enough time, all H’s will be replaced with halogens.



Halogenation (Continued)• Many organic reactions yield a mixture of products.

• It is not always necessary to balance the equation for an organic reaction as long as the reactant, the major product, and any necessary reagents and conditions are shown.

• In using this convention, it is customary to put reactants and reagents above the arrow and conditions, solvents, and catalysts below the arrow.


12.9 Cycloalkanes

• A cycloalkane is an alkane that contains a ring of carbon atoms.

• To form a closed ring requires an additional C–C bond and the loss of 2 H atoms.

• The general formula for cycloalkanes is CnH2n.

• Compounds of ring sizes from 3 through 30 and beyond have been prepared in the laboratory.


12.9 Cycloalkanes

• The C–C–C bond angles in cyclopropane are 60°, and the bond angles in cyclobutane are 90°, much less than the ideal 109.5° tetrahedral angle.

• These compounds are less stable and more reactive than other cycloalkanes.


12.9 Cycloalkanes

• The C–C–C bond angles in cyclopentane and cyclohexane are near ideal.

• Both cyclopentane and cyclohexane rings are stable, and many naturally occurring and biochemically active molecules, such as steroids, contain such rings.


12.9 Cycloalkanes

Properties of Cycloalkanes• Cyclic and acyclic alkanes are similar in many of their

properties. • Cyclopropane and cyclobutane are gases at room

temperature, whereas larger cycloalkanes are liquids or solids.

• Cycloalkanes are nonpolar, insoluble in water, and flammable.

• Because of their cyclic structures, cycloalkane molecules are more rigid and less flexible than their open-chain counterparts.

• Rotation is not possible around the carbon–carbon bonds in cycloalkanes without breaking open the ring.


12.9 Cycloalkanes

Surprising Uses of Petroleum• Petroleum is a mixture of hydrocarbons of varying

sizes. • Petroleum’s worth as a portable, energy-dense fuel

and as the starting point of many industrial chemicals makes it one of the world’s most important commodities.

• 90% of vehicular fuel needs worldwide are being met by oil. In addition, 40% of total energy consumption in the United States is petroleum-based.

• Petrochemicals are chemical products derived specifically from petroleum and generally refer to those products that are not used for fuels.


12.9 Cycloalkanes

Surprising Uses of Petroleum (Continued)• When crude oil is refined and “cracked,” the primary

petrochemicals obtained can be broken down into three categories:1. Alkenes: Primarily ethylene, propylene, and butadiene.

Ethylene and propylene are important sources of industrial chemicals and plastics products.

2. Aromatics: Most important among these are benzene, toluene, and the xylenes. These raw materials are used for making a variety of compounds, from dyes and synthetic detergents, to plastics and synthetic fibers, to pharmaceutical starting materials.

3. Synthesis gas: A mixture of carbon monoxide and hydrogen used to make ammonia, which is used to make fertilizer, and methanol, which is used as both a solvent and feedstock for other products.


12.9 Cycloalkanes

Surprising Uses of Petroleum (Continued)• Numerous types of products are made from

these petrochemicals:

– Lubricants, such as light machine oils, motor oils, and greases

– Paraffin waxes

– Synthetic rubber

– Plastics

– Petroleum jelly, once considered a nuisance by-product of oil drilling.



• Line structures are used almost exclusively in drawing cycloalkanes, with polygons used for the cyclic parts of the molecules.



• Cycloalkanes are named by a straightforward extension of the rules for naming open-chain alkanes:

• STEP 1: Use the cycloalkane name as the parent. If there is only one substituent on the ring, it is not necessary to assign a number because all ring positions are identical.

• STEP 2: Identify and number the substituents. Start numbering at the group that has alphabetical priority, and proceed around the ring in the direction that gives the second substituent the lower possible number.


Chapter Summary

1. What are the basic properties of organic compounds?

• Compounds made up primarily of carbon atoms are classified as organic.

• Many organic compounds contain carbon atoms that are joined in long chains by a combination of single double or triple bonds.

• In this chapter we focused primarily on alkanes, hydrocarbon compounds that contain only single bonds between all C atoms.


Chapter Summary, Continued

2. What are functional groups, and how are they used to classify organic molecules?

• Organic compounds can be classified into various families according to the functional groups they contain.

• A functional group is part of a larger molecule and is composed of a group of atoms that has characteristic structure and chemical reactivity.

• A given functional group undergoes nearly the same chemical reactions in every molecule where it occurs.



3. What are isomers? • Isomers are compounds that have the same

formula but different structures. • Isomers that differ in their connections among

atoms are called constitutional isomers. • When atoms other than carbon and hydrogen

are present the ability to have functional group isomers arises.

• Isomers are molecules that, due to the differences in their connections, have not only different structures, but belong to different families of organic molecules.



4. How are organic molecules drawn?

• Organic compounds can be represented by structural formulas in which all atoms and bonds are shown.

• By condensed structures in which not all bonds are drawn.

• By line structures in which the carbon skeleton is represented by lines and the locations of C and H atoms are understood.


Chapter Summary, Continued5. What are alkanes and cycloalkanes, and how are they

named? • Compounds that contain only carbon and hydrogen are called

hydrocarbons, and hydrocarbons that have only single bonds are called alkanes.

• A straight-chain alkane has all its carbons connected in a row, a branched-chain alkane has a branching connection of atoms somewhere along its chain, and a cycloalkane has a ring of carbon atoms.

• Alkanes have the general formula CnH2n+2, whereas cycloalkanes have the formula CnH2n.

• Straight-chain alkanes are named by adding the family ending -ane to a parent; this tells how many carbon atoms are present.

• Branched-chain alkanes are named by using the longest continuous chain of carbon atoms for the parent and then identifying the alkyl groups present as branches off the main chain.

• The position of the substituent groups on the main chain are identified by numbering the carbons in the chain so that the substituents have the lowest number.

• Cycloalkanes are named by adding cyclo- to the name of the alkane.



6. What are the general properties and chemical reactions of alkanes?

• Alkanes are generally soluble only in nonpolar organic solvents, have weak intermolecular forces, and are nontoxic.

• Their principal chemical reactions are combustion, a reaction with oxygen that gives carbon dioxide and water, and halogenation, a reaction in which hydrogen atoms are replaced by chlorine or bromine.

© 2013 Pearson Education, Inc. Outline 12.1The Nature of Organic Molecules 12.2Families of Organic...

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