Download Chapter 3

Chapter 3
An Introduction to
Organic Compounds
Nomenclature, Physical
Properties, and
Representation of
Structure
Paula Yurkanis Bruice
University of California,
Santa Barbara
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When Y Reacts, Z is Synthesized
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Alkanes are Hydrocarbons That Contain Only Single Bonds
General Molecular Formula: CnH2n+2
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Homologues
Homologues differ by a CH2 group.
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Nomenclature of Alkanes
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Nomenclature of Alkanes
C4H8 can be arranged in two ways:
C5H10 can be arranged in three ways:
These are constitutional isomers:
the same molecular formula but the atoms are linked differently.
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Nomenclature of Alkanes
C5H12 can be arranged in five ways:
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Nomenclature of Alkanes
C7H16 can be arranged in nine ways
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Alkyl Substituents
Removing a hydrogen from an alkane results in an alkyl substituent.
Replace “ane” of alkane with “yl.”
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Common Names
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Propyl and Isopropyl
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Two Ways to Draw Isopropyl Chloride
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There Are Four Butyl Groups
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n = An Unbranched Chain
Common names sometimes use “n” to indicate an straight-chain alkane.
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Primary, Secondary, and Tertiary Carbons
A primary carbon is bonded to one carbon.
A secondary carbon is bonded to two carbons.
A tertiary carbon is bonded to three carbons.
Primary hydrogens are attached to primary carbons.
Secondary hydrogens are attached to secondary carbons.
Tertiary hydrogens are attached to tertiary carbons.
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sec-Pentyl is Not a Good Name
A name must specify only one compound.
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“Tert” Can Be Used with
“Butyl” and “Pentyl”
Tert-hexyl is not a good name.
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“Iso”
Iso is at one end, and the substituent is at the other end.
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Alkyl Group Names
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Alkanes Systematic Nomenclature
First identify the longest continuous chain
(the parent hydrocarbon).
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Add the Name of the Substituent
Number the chain in the direction that gives the
substituent as low a number as possible.
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Common versus Systematic
Nomenclature
• Common names never have numbers.
• Only systematic names have numbers.
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List Substituents in Alphabetical Order
• The correct name is the one that contains the
lowest of the possible numbers.
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Multiple Substituents
•Chain is numbered in the direction that puts the lowest number in the name.
•Substituents are listed in alphabetical order (di- and tri- are not alphabetized).
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When Both Have the Same Lowest Number
When both names have the same lowest number,
go for the next lowest number.
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When Both Have the Same Number
When the same numbers are obtained in both directions,
the first group listed gets the lower number.
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Branched Substituents
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Chains with the Same Length
When two or more chains have the same length,
the parent hydrocarbon is the chain with the most substituents.
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Cycloalkanes
Skeletal structures do not show Cs and Hs bonded to Cs.
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Skeletal Structures
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Mono-Substituted Cycloalkanes
A number is not needed.
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Di-Substituted Cycloalkanes
• Substituents are stated in alphabetical order.
• #1 goes to first-listed substituent.
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Two Substituents with the
Same Low Number
If more than one name has the same low number,
choose the name with the next lowest number.
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Skeletal Structures
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Classification of Alkyl Halides
• Primary = Halogen is on a primary carbon.
• Secondary = Halogen is on a secondary carbon.
• Tertiary = Halogen is on a tertiary carbon.
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Common versus
Systematic Nomenclature
• Numbers are used only for systematic names.
• Common names never have numbers.
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Nomenclature of Alkyl Halides
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Ethers
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Common Names of Ethers
The substituents are listed in alphabetical order.
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Systematic Names of Ethers
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Classification of Alcohols
Primary alcohol = OH is on a primary carbon.
Secondary alcohol = OH is on a secondary carbon.
Tertiary alcohol = OH in on a tertiary carbon.
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Common Names of Alcohols
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Systematic Names of Alcohols
• The OH is the “functional group.”
• Systematic nomenclature uses a suffix to denote
a functional group.
• Alcohols are named by replacing the “e” at the
end of the parent hydrocarbon with the suffix “ol.”
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Systematic Names of Alcohols
When there is both a functional group and a
substituent, the functional group gets the lowest
number.
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Systematic Names of Alcohols
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Systematic Names of Diols
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Systematic Names of Alcohols
• The parent hydrocarbon is the longest chain that
contains the functional group.
• Number the chain in the direction that gives the
functional group the lowest possible number.
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Systematic Names of Alcohols
Pay attention to the number of the substituent
only if you get the same number for the
functional group in both directions.
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Systematic Names of Alcohols
If there is more than one substituent, they are listed in alphabetical order.
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A Substituent is a Prefix
A Functional Group is a Suffix
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Classification of Amines
The classification depends on how many groups are bonded to N.
•
Primary amine
•
Secondary amine = two groups bonded N
•
Tertiary amine
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= one group bonded to N
= three groups bonded N
Amines versus
Alkyl Halides and Alcohols
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Common Names of Amines
• Substituents are in alphabetical order followed
by “amine.”
• They are all written as one word.
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Systematic Names of Amines
• The suffix “amine” denotes the amine
functional group.
• The “e” at the end of the alkane name is
replaced by “amine.”
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Systematic Names of Amines
• A substituent on the chain is indicated by a number.
• A substituent on the nitrogen is indicated by an “N.”
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Quaternary Ammonium Salts
When there are four groups bonded to the N,
the groups are stated in alphabetical order
followed by “ammonium” and then the name of the anion.
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Summary of Nomenclature
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The Structure of an Alkyl Halide
The C—X bond of an alkyl halide becomes longer and weaker
as the size of the halogen increases.
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The Structure of an Alcohol
Resembles the Structure of Water
An alcohol is structurally like water with one H replaced by an R.
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The Structure of an Alcohol
Resembles the Structure of Water
An ether is structurally like water with both Hs replaced by Rs.
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Structures of Amines
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Boiling Points
The greater the attractive forces between molecules,
the higher the boiling point.
attractive forces
van der Waals forces
dipole–dipole interactions
hydrogen bonds
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Boiling Points
•
•
•
•
•
•
•
•
Methane 167.7 °C
Ethane
–88.6 °C
Propane –42.1 °C
Butane
–0.5 °C
Pentane
36.1 °C
Hexane
68.7 °C
Heptane
98.4 °C
Octane
125.7 °C
induced dipole-induced dipole
interactions
van der Waals forces
The greater the surface area of the molecule, the higher the bp.
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Branching Lowers the Boiling Point
“cigar”
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“tennis ball”
Dipole–Dipole Interactions
Dipole–dipole interactions are
stronger than van der Waals forces.
Van der Waals
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Van der Waals
dipole–dipole
Comparative Boiling Points
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Comparative Boiling Points
The larger the halogen, the more polarizable it is.
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Hydrogen Bonds in H2O and NH3
CH4 –167.7 °C
H2O 100 °C
no hydrogen bonds
hydrogen bonds
Hydrogen bonds are stronger than other dipole–dipole interactions.
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Hydrogen Bonds in Water
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Hydrogen Bonds in Amines
Hydrogen bonds are stronger in primary amines than in secondary amines
because primary amines have stronger dipole–dipole interactions.
Tertiary amines cannot form hydrogen bonds with each other.
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Hydrogen Bonds in Proteins
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Hydrogen Bonds in DNA
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Compounds with Similar Shapes and Properties
Often Have Similar Physiological Activities
Drugs bind to their receptors by van der Waals interactions,
dipole-dipole interactions, and hydrogen bonding.
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Melting Points
The mp is influenced by the packing of the molecules in the crystal lattice
alkanes with an odd number of carbons pack less tightly.
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Solubility
like dissolves like
Polar compounds dissolve in polar solvents (H2O).
Nonpolar compounds dissolve in nonpolar solvents (hexane).
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Solvation
Solvation is the interaction between solute molecules and solvent molecules.
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An Oxygen Can Drag
Three Carbons Into Water
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“Like Dissolves Like” is Important in Drug Action
Crossing the blood–brain barrier requires a fat-soluble drug.
THC and barbiturates have a hydrocarbon tail to facilitate crossing the barrier.
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Solubilities of Alkyl Halides
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A Cell Membrane
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Rotation Occurs About
Single Bonds
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Staggered and Eclipsed Conformers
of Ethane
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A Staggered Conformer is More Stable
Than an Eclipsed Conformer
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Rotation Can Occur About the
Three Carbon—Carbon Bonds in Butane
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Rotation About C-2—C-3 in Butane
Steric strain is repulsion between the electron clouds of atoms or groups.
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Zigzag Arrangement
OH
O
ChemDraw
1-pentanol
butyl ethyl ether
NH2
1-octanamine
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Br
1-bromohexane
Bond Angles in Planar Cyclic Alkanes
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Angle Strain
tetrahedral bond angle = 109.5°
bond angle < 109.5°
Angle strain results from poor orbital–orbital overlap because
bonds have to deviate from the ideal (109.5°) bond angle.
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Cyclopropane
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Cyclobutane
Molecules twist out of a planar arrangement
to minimize angle strain and the number of eclipsed hydrogens.
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Cyclopentane
Molecules twist out of a planar arrangement to
minimize angle strain and the number of eclipsed hydrogens.
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Chair Conformer of Cyclohexane
The chair conformer of cyclohexane is completely free of strain.
All bond angles are 111° and all adjacent bonds are eclipsed.
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Drawing the Chair Conformer
Notice that each equatorial bond is parallel to two ring bonds.
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Axial and Equatorial Bonds
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Ring Flip
Cyclohexane interconverts between two stable chair conformers.
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The Boat Conformer of Cyclohexane
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Conformers of Cyclohexane
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Conformers of Monosubstituted
Cyclohexanes
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A Substituent is More Stable in an
Equatorial Position
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1,3-Diaxial Interactions
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Comparing Conformers
Gauche is 0.87 kcal/mole
less sable than anti.
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Axial is 1.74 (2 × 0.87) kcal/mol
less sable than equatorial.
The larger the substituent,
the more the equatorial-substituted
conformer will be favored.
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The Only Difference Between Starch and Cotton
is an Equatorial Bond Versus an Axial Bond
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Cis and Trans Isomers
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Each Isomer Has
Two Chair Conformers
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This Chair Conformer
Has Four Diaxial Interactions
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cis-1-tert-butyl-3-methylcyclohexane
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trans-1-tert-butyl-3-methylcyclohexane
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Rings Can Be
Trans Fused or Cis Fused
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The Steroid Ring System
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