Chapter 2
Structure and Properties
of Organic Molecules
Organic Chemistry,5th Edition
L,G,Wade,Jr.
Jo Blackburn
Richland College,Dallas,TX
Dallas County Community College District
2003,Prentice Hall
Chapter 2 2
Wave Properties
of Electrons
Standing wave vibrates in fixed location.
Wave function,?,mathematical
description of size,shape,orientation
Amplitude may be positive or negative
Node,amplitude is zero
+_+
- =>
Chapter 2 3
Wave Interactions
Linear combination of atomic orbitals
between different atoms is bond formation
on the same atom is hybridization.
Conservation of orbitals
Waves that are in phase add together.
Amplitude increases.
Waves that are out of phase cancel out,
=>
Chapter 2 4
Sigma Bonding
Electron density lies between the nuclei.
A bond may be formed by s-s,p-p,s-p,
or hybridized orbital overlaps.
The bonding MO is lower in energy than
the original atomic orbitals.
The antibonding MO is higher in energy
than the atomic orbitals,
=>
Chapter 2 5
H2,s-s overlap
=>
Chapter 2 6
Cl2,p-p overlap
=>
Constructive overlap along the same
axis forms a sigma bond.
Chapter 2 7
HCl,s-p overlap
Question,
Draw the predicted shape for
the bonding molecular orbital and
the antibonding molecular orbital
of the HCl molecule,
Answer,See bottom of page 42 in your text.
=>
Chapter 2 8
Pi Bonding
Pi bonds form after sigma bonds.
Sideways overlap of parallel p orbitals.
=>
Chapter 2 9
Multiple Bonds
A double bond (2 pairs of shared electrons)
consists of a sigma bond and a pi bond.
A triple bond (3 pairs of shared electrons)
consists of a sigma bond and two pi bonds.
=>
Chapter 2 10
Molecular Shapes
Bond angles cannot be explained with simple
s and p orbitals,Use VSEPR theory.
Hybridized orbitals are lower in energy
because electron pairs are farther apart.
Hybridization is LCAO within one atom,just
prior to bonding,
=>
Chapter 2 11
sp Hybrid Orbitals
2 VSEPR pairs
Linear electron
pair geometry
180° bond
angle
=>
Chapter 2 12
sp2 Hybrid Orbitals
3 VSEPR pairs
Trigonal planar e- pair geometry
120° bond angle
=>
Chapter 2 13
sp3 Hybrid Orbitals
4 VSEPR pairs
Tetrahedral e- pair geometry
109.5° bond angle
=>
Chapter 2 14
Sample Problems
Predict the hybridization,geometry,and
bond angle for each atom in the
following molecules:
Caution! You must start with a good
Lewis structure!
NH2NH2
CH3-C?C-CHO
C H 3 C
O
C H 2
_ =>
Chapter 2 15
Rotation around Bonds
Single bonds freely rotate.
Double bonds cannot rotate unless the
bond is broken.
=>
Chapter 2 16
Isomerism
Molecules which have the same
molecular formula,but differ in the
arrangement of their atoms,are called
isomers.
Constitutional (or structural) isomers
differ in their bonding sequence.
Stereoisomers differ only in the
arrangement of the atoms in space,=>
Chapter 2 17
Structural Isomers
C H 3 O C H 3 a n d C H 3 C H 2 O H
C H 3
C H 3
a n d
=>
Chapter 2 18
Stereoisomers
C C
B r
C H 3
B r
H 3 C
C C
C H 3
B r
B r
H 3 C
a n d
Cis - same side Trans - across
Cis-trans isomers are also called geometric isomers.
There must be two different groups on the sp2 carbon.
C C
H 3 C
H H
H
No cis-trans isomers possible
=>
Chapter 2 19
Bond Dipole Moments
are due to differences in electronegativity.
depend on the amount of charge and
distance of separation.
In debyes,
=?4.8x? (electron charge) x d(angstroms)
=>
Chapter 2 20
Molecular Dipole Moments
Depend on bond polarity and bond angles,
Vector sum of the bond dipole moments.
Lone pairs of electrons contribute to the
dipole moment.
=>
Chapter 2 21
Intermolecular Forces
Strength of attractions between
molecules influence m.p.,b.p.,and
solubility; esp,for solids and liquids.
Classification depends on structure.
Dipole-dipole interactions
London dispersions
Hydrogen bonding
=>
Chapter 2 22
Dipole-Dipole Forces
Between polar molecules
Positive end of one molecule aligns with
negative end of another molecule.
Lower energy than repulsions,so net
force is attractive.
Larger dipoles cause higher boiling points
and higher heats of vaporization,
=>
Chapter 2 23
Dipole-Dipole
=>
Chapter 2 24
London Dispersions
Between nonpolar molecules
Temporary dipole-dipole interactions
Larger atoms are more polarizable.
Branching lowers b.p,because of
decreased surface contact between
molecules.
=>
C H 3 C H 2 C H 2 C H 2 C H 3
n - p e n t a n e,b,p,= 3 6癈
C H 3 C H
C H 3
C H 2 C H 3
i s o p e n t a n e,b,p,= 2 8癈
C
C H 3
C H 3
C H 3
H 3 C
n e o p e n t a n e,b,p,= 1 0癈
Chapter 2 25
Dispersions
=>
Chapter 2 26
Hydrogen Bonding
Strong dipole-dipole attraction
Organic molecule must have N-H or O-H.
The hydrogen from one molecule is
strongly attracted to a lone pair of
electrons on the other molecule.
O-H more polar than N-H,so stronger
hydrogen bonding =>
Chapter 2 27
H Bonds
=>
Chapter 2 28
Boiling Points and
Intermolecular Forces
C H 3 C H 2 O H
e t h a n o l,b,p,= 7 8 癈
C H 3 O C H 3
d i m e t h y l e t h e r,b,p,= - 2 5 癈
t r i m e t h y l a m in e,b,p,3,5 癈
N C H 3H 3 C
C H 3
p r o p y l a m in e,b,p,4 9 癈
C H 3 C H 2 C H 2 N
H
H
e t h y l m e t h y l a m in e,b,p,3 7 癈
N C H 3C H 3 C H 2
H
=>C H 3 C H 2 O H
e t h a n o l,b,p,= 7 8 癈 e th y l a m i n e,b,p,1 7 癈
C H 3 C H 2 N H 2
Chapter 2 29
Solubility
Like dissolves like
Polar solutes dissolve in polar solvents.
Nonpolar solutes dissolve in nonpolar
solvents.
Molecules with similar intermolecular
forces will mix freely,
=>
Chapter 2 30
Ionic Solute with
Polar Solvent
Hydration releases energy.
Entropy increases,=>
Chapter 2 31
Ionic Solute with
Nonpolar Solvent
=>
Chapter 2 32
Nonpolar Solute with
Nonpolar Solvent
=>
Chapter 2 33
Nonpolar Solute
with Polar Solvent
=>
Chapter 2 34
Classes of Compounds
Classification based on functional group
Three broad classes
Hydrocarbons
Compounds containing oxygen
Compounds containing nitrogen
=>
Chapter 2 35
Hydrocarbons
Alkane,single bonds,sp3 carbons
Cycloalkane,carbons form a ring
Alkene,double bond,sp2 carbons
Cycloalkene,double bond in ring
Alkyne,triple bond,sp carbons
Aromatic,contains a benzene ring
=>
Chapter 2 36
Compounds Containing
Oxygen
Alcohol,R-OH
Ether,R-O-R'
Aldehyde,RCHO
Ketone,RCOR'
C H 3 C H 2 C
O
H
C H 3 C
O
C H 3
=>
Chapter 2 37
Carboxylic Acids
and Their Derivatives
Carboxylic Acid,RCOOH
Acid Chloride,RCOCl
Ester,RCOOR'
Amide,RCONH2
C
O
O H
C
O
C l
C
O
O C H 3C
O
N H 2
=>
Chapter 2 38
Compounds Containing
Nitrogen
Amines,RNH2,RNHR',or R3N
Amides,RCONH2,RCONHR,RCONR2
Nitrile,RCN
N
O
C H 3
C H 3 C N
=>
Chapter 2 39
End of Chapter 2
Structure and Properties
of Organic Molecules
Organic Chemistry,5th Edition
L,G,Wade,Jr.
Jo Blackburn
Richland College,Dallas,TX
Dallas County Community College District
2003,Prentice Hall
Chapter 2 2
Wave Properties
of Electrons
Standing wave vibrates in fixed location.
Wave function,?,mathematical
description of size,shape,orientation
Amplitude may be positive or negative
Node,amplitude is zero
+_+
- =>
Chapter 2 3
Wave Interactions
Linear combination of atomic orbitals
between different atoms is bond formation
on the same atom is hybridization.
Conservation of orbitals
Waves that are in phase add together.
Amplitude increases.
Waves that are out of phase cancel out,
=>
Chapter 2 4
Sigma Bonding
Electron density lies between the nuclei.
A bond may be formed by s-s,p-p,s-p,
or hybridized orbital overlaps.
The bonding MO is lower in energy than
the original atomic orbitals.
The antibonding MO is higher in energy
than the atomic orbitals,
=>
Chapter 2 5
H2,s-s overlap
=>
Chapter 2 6
Cl2,p-p overlap
=>
Constructive overlap along the same
axis forms a sigma bond.
Chapter 2 7
HCl,s-p overlap
Question,
Draw the predicted shape for
the bonding molecular orbital and
the antibonding molecular orbital
of the HCl molecule,
Answer,See bottom of page 42 in your text.
=>
Chapter 2 8
Pi Bonding
Pi bonds form after sigma bonds.
Sideways overlap of parallel p orbitals.
=>
Chapter 2 9
Multiple Bonds
A double bond (2 pairs of shared electrons)
consists of a sigma bond and a pi bond.
A triple bond (3 pairs of shared electrons)
consists of a sigma bond and two pi bonds.
=>
Chapter 2 10
Molecular Shapes
Bond angles cannot be explained with simple
s and p orbitals,Use VSEPR theory.
Hybridized orbitals are lower in energy
because electron pairs are farther apart.
Hybridization is LCAO within one atom,just
prior to bonding,
=>
Chapter 2 11
sp Hybrid Orbitals
2 VSEPR pairs
Linear electron
pair geometry
180° bond
angle
=>
Chapter 2 12
sp2 Hybrid Orbitals
3 VSEPR pairs
Trigonal planar e- pair geometry
120° bond angle
=>
Chapter 2 13
sp3 Hybrid Orbitals
4 VSEPR pairs
Tetrahedral e- pair geometry
109.5° bond angle
=>
Chapter 2 14
Sample Problems
Predict the hybridization,geometry,and
bond angle for each atom in the
following molecules:
Caution! You must start with a good
Lewis structure!
NH2NH2
CH3-C?C-CHO
C H 3 C
O
C H 2
_ =>
Chapter 2 15
Rotation around Bonds
Single bonds freely rotate.
Double bonds cannot rotate unless the
bond is broken.
=>
Chapter 2 16
Isomerism
Molecules which have the same
molecular formula,but differ in the
arrangement of their atoms,are called
isomers.
Constitutional (or structural) isomers
differ in their bonding sequence.
Stereoisomers differ only in the
arrangement of the atoms in space,=>
Chapter 2 17
Structural Isomers
C H 3 O C H 3 a n d C H 3 C H 2 O H
C H 3
C H 3
a n d
=>
Chapter 2 18
Stereoisomers
C C
B r
C H 3
B r
H 3 C
C C
C H 3
B r
B r
H 3 C
a n d
Cis - same side Trans - across
Cis-trans isomers are also called geometric isomers.
There must be two different groups on the sp2 carbon.
C C
H 3 C
H H
H
No cis-trans isomers possible
=>
Chapter 2 19
Bond Dipole Moments
are due to differences in electronegativity.
depend on the amount of charge and
distance of separation.
In debyes,
=?4.8x? (electron charge) x d(angstroms)
=>
Chapter 2 20
Molecular Dipole Moments
Depend on bond polarity and bond angles,
Vector sum of the bond dipole moments.
Lone pairs of electrons contribute to the
dipole moment.
=>
Chapter 2 21
Intermolecular Forces
Strength of attractions between
molecules influence m.p.,b.p.,and
solubility; esp,for solids and liquids.
Classification depends on structure.
Dipole-dipole interactions
London dispersions
Hydrogen bonding
=>
Chapter 2 22
Dipole-Dipole Forces
Between polar molecules
Positive end of one molecule aligns with
negative end of another molecule.
Lower energy than repulsions,so net
force is attractive.
Larger dipoles cause higher boiling points
and higher heats of vaporization,
=>
Chapter 2 23
Dipole-Dipole
=>
Chapter 2 24
London Dispersions
Between nonpolar molecules
Temporary dipole-dipole interactions
Larger atoms are more polarizable.
Branching lowers b.p,because of
decreased surface contact between
molecules.
=>
C H 3 C H 2 C H 2 C H 2 C H 3
n - p e n t a n e,b,p,= 3 6癈
C H 3 C H
C H 3
C H 2 C H 3
i s o p e n t a n e,b,p,= 2 8癈
C
C H 3
C H 3
C H 3
H 3 C
n e o p e n t a n e,b,p,= 1 0癈
Chapter 2 25
Dispersions
=>
Chapter 2 26
Hydrogen Bonding
Strong dipole-dipole attraction
Organic molecule must have N-H or O-H.
The hydrogen from one molecule is
strongly attracted to a lone pair of
electrons on the other molecule.
O-H more polar than N-H,so stronger
hydrogen bonding =>
Chapter 2 27
H Bonds
=>
Chapter 2 28
Boiling Points and
Intermolecular Forces
C H 3 C H 2 O H
e t h a n o l,b,p,= 7 8 癈
C H 3 O C H 3
d i m e t h y l e t h e r,b,p,= - 2 5 癈
t r i m e t h y l a m in e,b,p,3,5 癈
N C H 3H 3 C
C H 3
p r o p y l a m in e,b,p,4 9 癈
C H 3 C H 2 C H 2 N
H
H
e t h y l m e t h y l a m in e,b,p,3 7 癈
N C H 3C H 3 C H 2
H
=>C H 3 C H 2 O H
e t h a n o l,b,p,= 7 8 癈 e th y l a m i n e,b,p,1 7 癈
C H 3 C H 2 N H 2
Chapter 2 29
Solubility
Like dissolves like
Polar solutes dissolve in polar solvents.
Nonpolar solutes dissolve in nonpolar
solvents.
Molecules with similar intermolecular
forces will mix freely,
=>
Chapter 2 30
Ionic Solute with
Polar Solvent
Hydration releases energy.
Entropy increases,=>
Chapter 2 31
Ionic Solute with
Nonpolar Solvent
=>
Chapter 2 32
Nonpolar Solute with
Nonpolar Solvent
=>
Chapter 2 33
Nonpolar Solute
with Polar Solvent
=>
Chapter 2 34
Classes of Compounds
Classification based on functional group
Three broad classes
Hydrocarbons
Compounds containing oxygen
Compounds containing nitrogen
=>
Chapter 2 35
Hydrocarbons
Alkane,single bonds,sp3 carbons
Cycloalkane,carbons form a ring
Alkene,double bond,sp2 carbons
Cycloalkene,double bond in ring
Alkyne,triple bond,sp carbons
Aromatic,contains a benzene ring
=>
Chapter 2 36
Compounds Containing
Oxygen
Alcohol,R-OH
Ether,R-O-R'
Aldehyde,RCHO
Ketone,RCOR'
C H 3 C H 2 C
O
H
C H 3 C
O
C H 3
=>
Chapter 2 37
Carboxylic Acids
and Their Derivatives
Carboxylic Acid,RCOOH
Acid Chloride,RCOCl
Ester,RCOOR'
Amide,RCONH2
C
O
O H
C
O
C l
C
O
O C H 3C
O
N H 2
=>
Chapter 2 38
Compounds Containing
Nitrogen
Amines,RNH2,RNHR',or R3N
Amides,RCONH2,RCONHR,RCONR2
Nitrile,RCN
N
O
C H 3
C H 3 C N
=>
Chapter 2 39
End of Chapter 2
