Chapter 3
Introduction
• The structural theory is the basis of organic
chemistry:
 Organic compounds can be grouped into families by
their common structural features
 The members of a given family often have similar
chemical and physical behavior
• Hydrocarbons - are organic molecules
consisting only of carbon (C)
and hydrogen (H) atoms.
Hydrocarbons
Aliphatic Hydrocarbons
Alkanes
Alkenes
Aromatic Hydrocarbons
Alkynes
I. Functional Groups
A.
Definition
B.
Types of Functional Groups
A. Definition
• Functional Group - is a group of atoms within a
larger molecule that
has a
characteristic chemical
reactivity
• It reacts in a typical way, generally independent of
the rest of the molecule
The chemistry of every organic molecule, regardless of
size and complexity, is determined by its functional groups.
B.
Types of Functional Groups
• Table 3.1 lists a wide variety of functional
groups.
• The functional groups of a compound affect:
• its reactions
• its structure
• its physical properties
Functional Groups with Carbon-Carbon
Multiple Bonds
Functional Group with Carbon-Carbon Multiple
Bonds: Alkene
• Alkenes have a
C-C double bond
Functional Group with Carbon-Carbon Multiple
Bonds: Alkyne
• Alkynes have a
C-C triple bond
Functional Group with Carbon-Carbon Multiple
Bonds: Arene
• Arenes have
special bonds that
are represented as
alternating single
and double C-C
bonds in a sixmembered ring
Functional Groups with Carbon Singly Bonded
to an Electronegative Atom
Functional Group with Carbon Singly Bonded
to an Electronegative Atom: Alkyl halide
• Alkyl halides have
a C bonded to a
halogen (C-X)
Functional Group with Carbon Singly Bonded
to an Electronegative Atom: Alcohol
• Alcohols have a
C bonded to O of
a hydroxyl group
(C-OH)
Functional Group with Carbon Singly Bonded
to an Electronegative Atom: Ether
• Ethers have two
C’s bonded to
the same O
(C-O-C)
Functional Group with Carbon Singly Bonded
to an Electronegative Atom: Amine
• Amines have a C
bonded to N
(C-N)
Functional Group with Carbon Singly Bonded
to an Electronegative Atom: Thiol
• Thiols have a C
bonded to SH
group (C-SH)
Functional Group with Carbon Singly Bonded
to an Electronegative Atom: Sulfide
• Sulfides have
two C’s bonded
to same S
(C-S-C)
Bonds are polar, with partial positive charge on C (+) and
partial negative charge (-) on electronegative atom
Functional Groups with Carbon-Oxygen
Double Bond (Carbonyl Groups)
• These compounds behave similarly but differ
depending on the identity of the atoms
attached on the carbonyl-group carbon.
Functional Groups with Carbon-Oxygen
Double Bond (Carbonyl Groups)
• Aldehydes: have one
hydrogen bonded to
C=O
• Ketones: have two
C’s bonded to the
C=O
Functional Groups with Carbon-Oxygen
Double Bond (Carbonyl Groups)
• Carboxylic Acids:
have -OH bonded to
the C=O
• Esters: have one
ether-like C-O
bonded to the C=O
Functional Groups with Carbon-Oxygen
Double Bond (Carbonyl Groups)
• Amides: have one
amine-like N bonded
to the C=O
• Acid chlorides: have
a Cl bonded to the
C=O
Carbonyl C has partial positive charge (+)
Carbonyl O has partial negative charge (-).
Practice Problem: Identify the functional groups in each of the
following molecules:
Practice Problem: Propose structures for simple molecules that
contain the following functional groups:
a. Alcohol
b. Aromatic ring
c. Carboxylic acid
d. Amine
e. Both ketone and amine
f. Two double bonds
Practice Problem: Identify the functional groups in the following
model of arecoline, a veterinary drug used to
control worms in animals. Convert the
drawing into a line-bond structure and a
molecular formula (red = O, blue = N)
II. Alkanes
A.
Alkane Isomers
B.
Alkyl Groups
C.
Naming Alkanes
D.
Properties of Alkanes
Overview
• Alkanes - are saturated aliphatic hydrocarbons.
• They are compounds that contain only carbons and
hydrogens (hydrocarbons), all connected exclusively by
single bonds (saturated)
• They are a large family of molecules
• Alkanes - have the general formula
CnH2n+2
where n is an integer
A. Alkane Isomers
• Isomers -
are different compounds with the
same molecular formula
Isomers
Constitutional Isomers
Stereoisomers
Enantiomers
Diastereomers
• For an alkane with less than three carbons, there is
only one possible structure.
• The molecular formula of an alkane with more than
three carbons can give more than one structure
• Straight-chain alkanes or normal alkanes - are
compounds whose carbons are connected in a
row.
• The C’s are connected to no more than 2 other C’s
• Branched-chain alkanes - are compounds whose
carbon chains branch.
• There are one or more C’s connected to 3 or 4 C’s
• Constitutional Isomers - are isomers that differ
in how their atoms are arranged in chains
• They are isomers with different connectivity, i.e different
order of attachment of their atoms
• Constitutional isomers may have:
Condensed Structures of Alkanes
• An alkane can be represented in a brief form
or in many types of extended form
• A condensed structure does not show bonds
but lists atoms, such as
 CH3CH2CH3 (propane)
 CH3C(CH3)2CH3 (2,2-dimethylpropane)
Practice Problem: Draw structures of the five isomers C6H14
Practice Problem: Propose structures that meet the following
descriptions
a. Two isomeric esters with the formula C5H10O2
b. Two isomeric nitriles with the formula C4H7N
Practice Problem: How many isomers are there with the
following descriptions?
a. Alcohols with the formula C3H8O
b. Bromoalkanes with the formula C4H9Br
B. Alkyl Groups
• AlkyI group - is the partial structure that remains
when a hydrogen atom is removed
from an alkane
- has the general abbreviation “R” (for
Radical, an incomplete species or
the “rest” of the molecule)
Naming Alkyl groups
• Replace -ane ending of alkane with -yl ending
-CH3 is “methyl” from methane
-CH2CH3 is “ethyl” from ethane
• Combining an alkyl group with any of the
functional groups gives the name of the
compound
Degree of a Carbon atom
 Degree (o) is applied to sp3 carbons only !
 Degree (o) of a carbon is equal to the number of
carbons attached directly to it.
1o primary
2o secondary
3o tertiary
4o quaternary
Types of Alkyl groups
Alkyl groups are classified by the connection site
 primary alkyl group (attached to 1oC)
 secondary alkyl group (attached to 2oC)
 tertiary alkyl group (attached to 3oC)
 quaternary alkyl group (attached to 4oC)
Naming Alkyl groups: Common System
• Free valence indicates carbon # 1
• Prefixes are necessary to indicate arrangement
of carbons in structure:
• n – unbranched chain and free valence is on 1o C
• iso – one -CH3 on next to last carbon
• sec – free valence on 2o C and used only for butyl
• tert – free valence is on 3o C
• neo – two -CH3’s next to the last carbon
• iso – one -CH3 on next to last carbon
• iso – one -CH3 on next to last carbon
• sec – free valence on 2o C and used only for butyl
• tert – free valence is on 3o C
• iso – one -CH3 on next to last carbon
• tert – free valence is on 3o C
• neo – two -CH3’s next to the last carbon
Degree of a Hydrogen atom
 Degree (o) of a hydrogen is the same as the o
of carbon to which it is attached
 No such thing as a quaternary H !
Practice Problem: Draw the eight 5-carbon alkyl groups (pentyl
isomers)
Practice Problem: Identify the carbon atoms in the following
molecules as primary, secondary, tertiary or
quaternary
Practice Problem: Identify the hydrogen atoms on the
compounds shown as primary, secondary,
or tertiary
Practice Problem: Draw structures of alkanes that meet the
following descriptions
a. An alkane with two tertiary carbons
b. An alkane that contains an isopropyl group
c. An alkane that has one quaternary and one
secondary carbon
C. Naming Alkanes
• The International Union of Pure and Applied Chemistry
(IUPAC) devised a system of nomenclature that uses:
Steps to naming alkanes1
1. Find the parent hydrocarbon
a. Find the longest continuous chain of carbon atoms
Steps to naming alkanes1
1. Find the parent hydrocarbon
a. Find the longest continuous chain of carbon atoms
b. If two chains have equal length, choose the main chain
with more substituents
Steps to naming alkanes2
2. Number the atoms in the main chain
•
The correct sequence is when the substituents have the
lowest possible number
Steps to naming alkanes3
3. Identify and number the substituents
•
Name and locate the substituents
Steps to naming alkanes4
4.
Write the name as a single word
a. Use hyphens to separate the different prefixes, and use
commas to separate numbers.
b. Use multiplicity prefixes di-, tri-, tetra-, …
b. Put the substituents in alphabetical order (Do not
consider multiplier prefixes)
Steps to naming alkanes5
5.
Name a complex substituent as though it were
itself a compound
a. Name the complex substituent using the point of
attachment as C#1
b. Put it in alphabetical order (numerical prefix is included)
c. Set it off in parentheses
Practice Problem: Give IUPAC names for the following
compounds
Practice Problem: Draw structures corresponding to the
following IUPAC names
a. 3,4-Dimethylnonane
b. 3-Ethyl-4,4-dimethylheptane
c. 2,2-Dimethyl-4-propyloctane
d. 2,2,4-Trimethylpentane
Practice Problem: Name the eight 5-carbon alkyl groups
Practice Problem: Give the IUPAC name for the following
hydrocarbon, and convert the drawing into
skeletal structure.
D.
Properties of Alkanes
• Alkanes are called paraffins (low affinity
compounds)
• They do not react as most chemicals, i.e. they are
chemically inert to most lab reagents
• However, they do react with O2, halogens and a few
other substances
Oxidation: Reaction with O2
• Alkanes will burn in a flame, producing carbon
dioxide, water, and heat
Alkane
O2
D
CO2 + H2O
DH = -
• The larger the value of DH, the less stable the alkane
• If hydrocarbons do not contain the same amount of
carbons, one must compare DH/CH2 rather than DH
Halogenation
• Alkanes react with Cl2 in the presence of light to
replace H’s with Cl’s (not controlled)
Alkane
• X2 = Br2 or Cl2
X2
hn
Alkyl halides + HX
Physical Properties
1.
Intermolecular Forces
2.
Solubility
1.
Intermolecular Forces
• To a first approx. C-H and C-C bonds are nonpolar:
• Dipole moments of alkanes are ~0
• Alkanes are nonpolar
• The IMF’s for alkanes are van der Waals interactions
(i.e induced-dipole-induced-dipole forces, London or
dispersion forces)
• For compounds of similar M.W., alkanes have lower
b.p’s and m.p’s.
• Boiling points and melting points increase as size
of alkane increases.
• This is due the presence of dispersion forces
• Dispersion forces are weak intermolecular forces
that arise due to transient nonuniform electron
distribution (temporary molecular dipoles).
• Increased branching lowers an alkane’s boiling point
Branched-chain alkanes are more nearly spherical than
straight-chain alkanes, thus have smaller surface areas,
and consequently have smaller dispersion forces.
Compounds
Boiling Point
Pentane
36.1 oC
Isopentane
27.85 oC
Neopentane
9.5oC
Octane
125.7oC
Isooctane
99.3oC
2.
Solubility
• “Like dissolves like”
• Alkanes are nonpolar; they dissolve best in
solvents which are either nonpolar or weakly
polar
# Carbons
4
~
# Hydrophilic sites
1
III. Cycloalkanes
A.
Naming Cycloalkanes
B.
Cis-Trans Isomerism
Overview
• Cycloalkanes – are alicyclic (aliphatic cyclic)
compounds
• They are alkanes that have carbon atoms that form a ring
• Their structure is shown as a regular polygon with the
number of vertices equal to the number of C’s
Simple Cycloalkanes
• Cycloalkanes – are rings of -CH2- units.
– have the general formula
CnH2n
where n is an integer
Complex Cycloalkanes
• Naturally occurring materials contain cycloalkane
structures
• Examples: chrysanthemic acid, prostaglandins, steroids
(cyclopropane)
(cyclopentane)
(cyclohexane and cyclopentane)
Properties of Cycloalkanes
• Boiling points increase as ring size increases.
• Melting points are affected by the shapes and the way
that crystals pack so they do not change uniformly
A.
Naming Cycloalkanes
• Cycloalkanes are also named by the rules devised by
the International Union of Pure and Applied Chemistry
(IUPAC).
Steps to naming cycloalkanes1
1. Find the parent hydrocarbon
a. Count the number of carbon atoms in the ring and the
number in the largest substituent chain
•
•
If # Cring = or > # Csubstituent, then it is named as an alkyl-substituted cycloalkane
If # Cring < # Csubstituent, then it is named as an cycloalkyl-substituted alkane
Steps to naming cycloalkanes2
2. Number the substituents and write the name
•
The correct sequence is when the substituents have the
lowest possible number
•
For an alkyl- or halo-substituted cycloalkane, start at a point of
attachment as C1 and number the substituents on the ring so that the
second substituent has as low a number as possible.
•
When two or more substituents could potentially be assigned the same
numbers, number them by alphabetical order.
When two or more substituents could potentially be assigned
the same numbers, number them by alphabetical order.
Practice Problem: Give IUPAC names for the following
cycloalkanes
Practice Problem: Draw structures corresponding to the
following IUPAC names
a. 1,1-Dimethylcyclooctane
b. 3-Cyclobutylhexane
c. 1,2-Dichlorocyclopentane
d. 1,3-Dibromo-5-methylcyclohexane
Practice Problem: Name the following cycloalkane
B.
Cis-Trans Isomerism
• In open-chain alkanes, free rotation is possible around
C-C bonds because s bonds are cylindrically
symmetrical:
• In cycloalkanes, free rotation is limited by the ring
structure
• The common ring sizes (C3, C4, C5, C6, C7) are severely
restricted in their molecular motions
• Larger cycloalkanes have increasingly more rotational freedom
• Rings have two “faces” and substituents are labeled
as to their relative facial positions
• There are two different 1,2-dimethyl-cyclopropane isomers:
one with the two methyls on
the same side (cis) of the ring
one with the methyls on opposite
sides (trans)
Stereoisomers
• Stereoisomers – are compounds with atoms
connected in the same order but which differ in
three-dimensional orientation
• The terms “cis” and “trans” should be used to specify stereoisomeric
ring structures
• Constitutional isomers – are compounds
with atoms connected in different order
Practice Problem: Name the following substances, including the
cis- or trans- prefix
Practice Problem: Name the following substances, including the
cis- or trans- prefix
Practice Problem: Draw the structures of the following molecules
a. trans-1-Bromo-3-methylcyclohexane
b. cis-1,2-Dimethylcyclobutane
c. trans-1-tert-Butyl-2-ethylcyclohexane
Practice Problem: Name the following substances, including the
cis- or trans- prefix (red-brown = Br)
IV. Bicyclic Alkane Systems
A.
Naming Bicyclic Systems
Overview
• Bicycloalkanes – are alkanes containing two
rings that share two carbon atoms
• Bridgehead atoms – are the shared carbon atoms
• Bridges – are the carbon chains connecting the bridgeheads
• Bicycloalkanes – have the general formula
CnH2n-2
where n is an integer
• Spiroalkanes – are cycloalkanes in which two
rings share only one carbon atom
A.
Naming Bicyclic Alkane Systems
• The International Union of Pure and Applied Chemistry
(IUPAC) has devised rules to name bicyclic alkane
systems.
Steps to naming bicycloalkanes1
1. Find the parent name
•
The parent name of a bicycloalkane is that of the
unbranched alkane of the same number of carbon
atoms as are in the bicyclic ring system
2. Numbering begins at one bridgehead carbon
atom
#1
#1
CH3
Steps to naming cycloalkanes2
3. Number the bridges in order of decreasing size
•
Longest bridge is written first
•
•
Proceed along the longest bridge to the second bridgehead
carbon, then along the next longest bridge back to the original
bridgehead carbon, and so on until all carbon atoms are
numbered.
If there are two bridges of the same length, the correct
sequence is when the substituents have the lowest
possible number
•
If there are more than one substituents, give an alphabetical
preference.
Steps to naming cycloalkanes3
4. Show the bridge lengths in brackets
•
Count the number of carbons linking the bridgeheads
and place them in decreasing order in brackets between
the prefix bicyclo and the parent name and with periods
separating each number.
CH3
Bicyclo [3.2.0] heptane
7-methylbicyclo [4.2.0]octane
Chapter 3