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Copyright  The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chapter 10. An Introduction to Organic Chemistry: The Saturated Hydrocarbons. Denniston Topping Caret 5 th Edition. 10.1 The Chemistry of Carbon. Why are there so many organic compounds?

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chapter 10
Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Chapter 10

An Introduction to Organic Chemistry:

The Saturated Hydrocarbons

Denniston Topping Caret

5th Edition

10 1 the chemistry of carbon
10.1 The Chemistry of Carbon

Why are there so many organic compounds?

  • Carbon forms stable, covalent bonds with other carbon atoms
  • Consider three allotropic forms of elemental carbon
    • Graphite in planar layers
    • Diamond is a three-dimensional network
    • Buckminsterfullerene is 60 C in a roughly spherical shape
why are there so many organic compounds

Why are there so many organic compounds?

10.1 The Chemistry of Carbon

Carbon atoms form stable bonds with other elements, such as:

Oxygen

Nitrogen

Sulfur

Halogen

Presence of these other elements confers many new physical and chemical properties on an organic compound

why are there so many organic compounds4

Why are there so many organic compounds?

10.1 The Chemistry of Carbon

Carbon atoms form double or triple bonds with:

Other carbon atoms (double & triple)

Oxygen (double only)

Nitrogen (double & triple)

These combinations act to produce a variety of organic molecules with very different properties

why are there so many organic compounds5

Why are there so many organic compounds?

10.1 The Chemistry of Carbon

Carbon atoms can be arranged with these other atoms; is nearly limitless

Branched chains

Ring structures

Linear chains

Two organic compounds may even have the same number and kinds of atoms but completely different structures and thus, different properties

These are called isomers

isomers
Many carbon compounds exist in the form of isomers

Isomers are compounds with the same molecular formula but different structures

An isomer example: both are C4H10 but have different structures

Butane

Methylpropane

Isomers

10.1 The Chemistry of Carbon

isomers7
Isomers

All have the same molecular formula: C4H8

10.1 The Chemistry of Carbon

important differences between organic and inorganic compounds
Important Differences Between Organic and Inorganic Compounds
  • Bond type
    • Organics have covalent bonds
      • Electron sharing
    • Inorganics usually have ionic bonds
      • Electron transfer
  • Structure
    • Organics
      • Molecules
      • Nonelectrolytes
    • Inorganics
      • Three-dimensional crystal structures
      • Often water-soluble, dissociating into ions -electrolytes

10.1 The Chemistry of Carbon

important differences between organic and inorganic compounds9
Important Differences Between Organic and Inorganic Compounds
  • Melting Point & Boiling Point
    • Organics have covalent bonds
      • Intermolecular forces broken fairly easily
    • Inorganics usually have ionic bonds
      • Ionic bonds require more energy to break
  • Water Solubility
    • Organics
      • Nonpolar, water insoluble
    • Inorganics
      • Water-soluble, readily dissociate

10.1 The Chemistry of Carbon

comparison of major properties of organic and inorganic compounds
Comparison of Major Properties of Organic and Inorganic Compounds

10.1 The Chemistry of Carbon

bonding characteristics and isomerism
Bonding Characteristics and Isomerism
  • One reason for the power of carbon is that it can form 4 covalent bonds
  • It appears to have only 2 available electrons
  • Carbon can hybridize its orbitals to move 2 electrons out of it 2s orbital

10.1 The Chemistry of Carbon

hybrid orbitals
Hybrid Orbitals
  • Each carbon-hydrogen bond in methane arises from an overlap of a C(sp3) and an H(1s) orbital
  • 4 equivalent sp3 orbitals point toward the corners of a regular tetrahedron
  • The 4 sp3 hybrid orbitals of carbon combine with the 1s orbitals on 4 H to produce methane – CH4

10.1 The Chemistry of Carbon

families of organic compounds
Families of Organic Compounds
  • Hydrocarbons contain only carbon

and hydrogen

  • They are nonpolar molecules
    • Not soluble in water
    • Are soluble in typical nonpolar organic solvents
      • Toluene
      • Pentane

10.1 The Chemistry of Carbon

families of organic compounds14
Families of Organic Compounds
  • Hydrocarbons are constructed of chains or rings of carbon atoms with sufficient hydrogen atoms to fulfill carbon’s need for four bonds
  • Substituted hydrocarbon is one in which one or more hydrogen atoms is replaced by another atom or group of atoms

10.1 The Chemistry of Carbon

division of the family of hydrocarbons
Division of the Family of Hydrocarbons

10.1 The Chemistry of Carbon

hydrocarbon saturation
Hydrocarbon Saturation
  • Alkanes are compounds that contain only carbon-carbon and carbon-hydrogen single bonds
    • A saturated hydrocarbon has no double or triple bonds
  • Alkenes and alkynes are unsaturated because they contain at least one carbon to carbon double or triple bond

10.1 The Chemistry of Carbon

cyclic structure of hydrocarbons
Cyclic Structure of Hydrocarbons
  • Some hydrocarbons are cyclic
    • Form a closed ring
    • Aromatic hydrocarbons contain a benzene ring or related structure

10.1 The Chemistry of Carbon

common functional groups
Common Functional Groups

10.1 The Chemistry of Carbon

10 2 alkanes
10.2 Alkanes
  • The general formula for a chain alkane is CnH2n+2
    • In this formula n = the number of carbon atoms in the molecule
  • Alkanes are saturated hydrocarbons
    • Contain only carbon and hydrogen
    • Bonds are carbon-hydrogen and carbon-carbon single bonds
formulas used in organic chemistry
Formulas Used in Organic Chemistry
  • Molecular formula - lists kind and number of each type of atom in a molecule, no bonding pattern
  • Structural formula - shows each atom and bond in a molecule
  • Condensed formula - shows all the atoms in a molecule in sequential order indicating which atoms are bonded to which
  • Line formula - assume a carbon atom at any location where lines intersect
    • Assume a carbon at the end of any line
    • Each carbon in the structure is bonded to the correct number of hydrogen atoms

10.2 Alkanes

the tetrahedral carbon atom
The Tetrahedral Carbon Atom

10.2 Alkanes

  • Lewis dot structure
  • The tetrahedral shape around the carbon atom
  • The tetrahedral carbon drawn with dashes and wedges
  • The stick drawing of the tetrahedral carbon atom
  • Ball and stick model of methane
drawing methane and ethane
Drawing Methane and Ethane

10.2 Alkanes

Staggered form of ethane

structural isomers
Butane

Bp –0.4 oC

Mp –139 oC

Isobutane

Bp –12 oC

Mp –145 oC

Structural Isomers
  • Constitutional/Structural Isomers differ in how atoms are connected
    • Two isomers of butane have different physical properties
    • The carbon atoms are connected in different patterns

10.2 Alkanes

comparison of physical properties of five isomers of hexane
Comparison of Physical Properties of Five Isomers of Hexane

Compare the basic linear structure of hexane

  • All other isomers have one or more carbon atoms branching from the main chain
  • Branched-chain forms of the molecule have a much smaller surface area
    • Intermolecular forces are weaker
    • Boiling and melting points are lower than straight chains

10.2 Alkanes

physical properties of organic molecules
Physical Properties of Organic Molecules
  • Nonpolar
  • Not water soluble
  • Soluble in nonpolar organic solvents
  • Low melting points
  • Low boiling points
  • Generally less dense (lighter) than water
  • As length (molecular weight) increases, melting and boiling points increase as does the density

10.2 Alkanes

properties of alkanes29
Properties of Alkanes
  • Most of the alkanes are hydrophobic:

water hating

  • Straight chain alkanes comprise a homologous series: compounds of the same functional class that differ by a –CH2- group
  • Nonpolar alkanes are:
    • Insoluble in water (a highly polar solvent)
    • Less dense than water and float on it

10.2 Alkanes

alkyl groups
Alkyl Groups

10.2 Alkanes

  • An alkyl group is an alkane with one hydrogen atom removed
  • It is named by replacing the -ane of the alkane name with -yl
  • Methane becomes a methyl group
alkyl groups31
Alkyl Groups
  • All six hydrogens on ethane are equivalent
  • Removing one H generates the ethyl group
  • All 3 structures shown at right are the same

10.2 Alkanes

alkyl group classification
Alkyl Group Classification
  • Alkyl groups are classified according to the number of carbons attached to the carbon atom that joins the alkyl group to a molecule
  • All continuous chain alkyl groups are 1º
  • Isopropyl and sec-butyl are 2º groups

10.2 Alkanes

iso alkyl groups
Iso- Alkyl Groups
  • Propane: removal of a hydrogen generates two different propyl groups depending on whether an end or center H is removed

10.2 Alkanes

n-propyl

isopropyl

sec alkyl groups
Sec- Alkyl Groups
  • n-butane gives two butyl groups depending on whether an end (1º) or interior (2º) H is removed

10.2 Alkanes

n-butyl

sec-butyl

more alkyl group classification
More Alkyl Group Classification
  • Isobutane gives two butyl groups depending on whether a 1o or 3o H is removed

10.2 Alkanes

1o C

3o C

isobutyl

t-butyl

nomenclature
Nomenclature
  • The IUPAC (International Union of Pure and Applied Chemistry) is responsible for chemical names
  • Before learning the IUPAC rules for naming alkanes, the names and structures of eight alkyl groups must be learned
  • These alkyl groups are historical names accepted by the IUPAC and integrated into modern nomenclature

10.2 Alkanes

iupac names for alkanes
IUPAC Names for Alkanes
  • The base or parent name for an alkane is determined by the longest chain of carbon atoms in the formula
    • The longest chain may bend and twist, it is seldom horizontal
    • Any carbon groups not part of the base chain are called branches or substituents
    • These carbon groups are also called alkyl groups

10.2 Alkanes

iupac names for alkanes41
IUPAC Names for Alkanes
  • Rule 1 applied
    • Find the longest chain in each molecule
  • A=7 B=8

10.2 Alkanes

iupac names for alkanes42
IUPAC Names for Alkanes
  • Number the carbon atoms in the chain starting from the end with the first branch
    • If both branches are equally from the ends, continue until a point of difference occurs

10.2 Alkanes

iupac names for alkanes43
1

6

7

8

2

4

5

3

2

1

3

4

5

6

this branch would be on C-4

if you started at correct C-8

7

IUPAC Names for Alkanes

Number the carbon atoms correctly

  • Left: first branch is on carbon 3
  • Right: first branch is on carbon 3 (From top) not carbon 4 (if number from right)

10.2 Alkanes

iupac names for alkanes44
IUPAC Names for Alkanes
  • Write each of the branches/substituents in alphabetical order before the base/stem name (longest chain)
    • Halogens usually come first
    • Indicate the position of the branch on the main chain by prefixing its name with the carbon number to which it is attached
    • Separate numbers and letters with a hyphen
    • Separate two or more numbers with commas

10.2 Alkanes

iupac names for alkanes45
IUPAC Names for Alkanes

10.2 Alkanes

Name : 4-ethyl-2-methylhexane

iupac names for alkanes46
IUPAC Names for Alkanes
  • Hyphenated and number prefixes are not considered when alphabetizing groups
    • Name the compound below
    • 5-sec-butyl-4-isopropylnonane

10.2 Alkanes

iupac names for alkanes47
IUPAC Names for Alkanes
  • When a branch/substituent occurs more than once
    • Prefix the name with
      • di
      • tri
      • tetra
    • Then list the number of the carbon branch for that substituent to the name with a separate number for each occurrence
      • Separate numbers with commas
  • e.g., 3,4-dimethyl or 4,4,6-triethyl

10.2 Alkanes

iupac names for alkanes48
IUPAC Names for Alkanes

10.2 Alkanes

5-ethyl-2,3-dimethylheptane

ethyl>dimethyl

practice iupac name
Practice: IUPAC Name

1

2

10.2 Alkanes

3

4

5

6

6-ethyl-6-isobutyl-3,3-dimethyldecane

7

8

9

10

10 3 cycloalkanes
10.3 Cycloalkanes
  • Cycloalkanes have two less hydrogens than the corresponding chain alkane
    • Hexane=C6H14; cyclohexane=C6H12
  • To name cycloalkanes, prefix cyclo- to the name of the corresponding alkane
    • Place substituents in alphabetical order before the base name as for alkanes
    • For multiple substituents, use the lowest possible set of numbers; a single substituent requires no number
cycloalkane structures
Cycloalkane Structures

Cyclopropane

Cyclobutane

Cyclohexane

10.3 Cycloalkanes

Type of Formula: Structural Condensed Line

naming a substituted cycloalkane
Naming a Substituted Cycloalkane

Name the two cycloalkanes shown below

  • Parent chain 6 carbon ring 5 carbon ring

cyclohexanecyclopentane

  • Substituent 1 chlorine atom a methyl group

chloromethyl

  • Name Chlorocyclohexane Methylcyclopentane

10.3 Cycloalkanes

cis trans isomers in cycloalkanes
cis-trans Isomers in Cycloalkanes
  • Atoms of an alkane can rotate freely around the carbon-carbon single bond having an unlimited number of arrangements
  • Rotation around the bonds in a cyclic structure is limited by the fact that all carbons in the ring are interlocked
    • Formation of cis-trans isomers, geometric isomers, is a consequence of the lack of free rotation
  • Stereoisomers are molecules that have the same structural formulas and bonding patterns, but different arrangements of atoms in space
    • cis-trans isomers of cycloalkanes are stereoisomers whose substituents differ in spatial arrangement

10.3 Cycloalkanes

cis trans isomers in cycloalkanes54
cis-trans Isomers in Cycloalkanes
  • Two groups may be on the same side (cis) of the imagined plane of the cycloring or they may be on the opposite side (trans)
  • Geometric isomers do not readily interconvert, only by breaking carbon-carbon bonds can they interconvert

10.3 Cycloalkanes

10 4 conformations of alkanes
10.4 Conformations of Alkanes
  • Conformations differ only in rotation about carbon-carbon single bonds
  • Two conformations of ethane and butane are shown
    • The first (staggered form) is more stable because it allows hydrogens to be farther apart and thus, the atoms are less crowded
two conformations of cyclohexane
Two Conformations of Cyclohexane

Chair form (more stable) Boat form

10.4 Conformations of Alkanes and Cycloalkanes

E=equitorial A=axial

10 5 reactions of alkanes
10.5 Reactions of Alkanes
  • Alkanes, cycloalkanes, and other hydrocarbons can be:
    • Oxidized (by burning) in the presence of excess molecular oxygen, in a process called combustion
    • Reacted with a halogen (usually chlorine or bromine) in a halogenation reaction
alkane reactions
Alkane Reactions

The majority of the reaction of alkanes are combustion reactions

  • Complete CH4 + 2O2 CO2+ 2H2O Complete combustion produces
      • Carbon dioxide and water
  • Incomplete 2CH4 + 3O2 2CO + 4H2O
    • Incomplete combustion produces
      • Carbon monoxide and water
      • Carbon monoxide is a poison that binds irreversibly to red blood cells

10.5 Reactions of Alkanes

halogenation
Halogenation

Halogenation is a type of substitution reaction, a reaction that results in a replacement of one group for another

  • Products of this reaction are:
    • Alkyl halide or haloalkane
    • Hydrogen halide
  • This reaction is important in converting unreactive alkanes into many starting materials for other products
  • Halogenation of alkanes ONLY occurs in the presence of heat and/or light (UV)

10.5 Reactions of Alkanes

petroleum processing
Petroleum Processing

10.5 Reactions of Alkanes

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