Electrostatic Potential Maps
Models that visually portray polarity and dipoles
Hydrogen Halides
Molecular Polarity
& Dipole Moment
When identical polar bonds
point in opposite directions,
the effects of their polarities
cancel, giving no net dipole
moment. When they do not
point in opposite directions,
there is a net effect and a net
molecular dipole moment,
designated d.
Molecular Dipole Moment
The vector sum of the magnitude and the direction of the individual
bond dipole determines the overall dipole moment of a molecule
An electrically
charged rod
attracts a stream
of chloroform but
has no effect on a
stream of carbon
tetrachloride.
Ammonia and in the Ammonium Ion
Water
Polarity & Physical Properties
Ozone and Water
0.1278 nm
•
•
Resultant Molecular Dipoles > 0
Solubility: Polar molecules that
dissolve or are dissolved in like
molecules
•
•
The Lotus flower
Water & dirt repellancy
The “Lotus Effect”
Biomimicry
http://bfi.org/biomimicry
Wax
• Lotus petals have micrometer-scale roughness, resulting
in water contact angles up to 170°
• See the Left image in the illustration on the right.
The “Lotus Effect”
Biomimicry
http://www.sciencemag.org/cgi/content/full/299/5611/1377/DC1
• Isotactic polypropylene (i-PP) melted between
two glass slides and subsequent crystallization
provided a smooth surface. Atomic force
microscopy tests indicated that the surface had
root mean square (rms) roughness of 10 nm.
• A) The water drop on the resulting surface had a
contact angle of 104° ± 2
• B) the water drop on a superhydrophobic i-PP
coating surface has a contact angle of 160°.
Science, 299, (2003), pp. 1377-1380, H. Yldrm Erbil, A.
Levent Demirel, Yonca Avc, Olcay Mert
Molecular Representations
Empirical Formula, Molecular Formula, Structure:
(Lewis, Kekule, Condensed, Line), Visual Model:
wireframe, stick, ball & stick, space filling, electrostatic,
energy surface
Draw bond-line structures for each of the four molecules.
ketone
1.
aldehyde
2.
carboxylic acid
3.
ester (carboxylic acid ester)
4.
O
COOCH3
or
O
O
1.
or
4.
3.
O
O
2.
H
NOT
OH
COOH
or
CO2H
OCH3
NOT
O
O
Question 12
• The molecular formula of morpholine is:
•
A)
C2HNO
•
B)
C4HNO
•
C) C4H4NO
•
D) C4H5NO
•
E) C4H9NO
Question 13
• The respective number of bonded pairs of
electrons and of unshared pairs of
electrons in morpholine is:
•
A) 7, 0
•
B) 7, 1
•
C) 15, 0
•
D) 15, 1
•
E) 15, 3
Formulas &
Kekulé / Condensed / Bond-Line
Structures / Drawings
Molecular formula?
Empirical Formula?
Bond-Line Structure?
Question 14
• The bond-line representation for
(CH3)2CHCH2CH2CHBrCH3 is
•
•
A)
B)
•
•
C)
D)
Question 15
Select the best condensed structural formula for
the following bond-line structure:
HO OH
H
O
A.
B.
C.
D.
E.
(CH3)2CHCH2COHOHCOH
CH3CH3CHCH2C(OH)2CHO
(CH3)2CHCH2C(OH)2CHO
(CH3)2CHCH2C(OH)2COH
CH3CHCH3CH2C(OH)2CHO
Line Drawing and Ball & Stick
8.16 Å (0.816 nm)
http://chemconnections.org/organic/chem226/Labs/Smell/SmellStereochem.html
Question 16
While on-line, click on the jmol-structure
on the left.
Which one of the formulas or
structural renderings that
follow is correct?
A)
C 2H3O
D)
O
B)
C)
H 3C
O
H
CH3 CH 2 OH
CH2 COOH
O
E)
OH
Question 17
• How many constitutional alcohol isomers
have the molecular formula C4H10O?
•
A) two
•
B) three
•
C) four
•
D) five
More Molecular Representations
Empirical Formula, Molecular Formula, Structure:
(Lewis, Kekule, Condensed, Line), Visual Model:
wireframe, stick, ball & stick, space filling,
electrostatic, energy surface
Worksheet: Organic Molecules 1
http://chemconnections.org/organic/chem226/Labs/VSEPR/
Very Large Molecules:DNA
http://www.umass.edu/microbio/chime/beta/pe_alpha/atlas/atlas.htm
Views & Algorithms
10.85 Å
10.85 Å
Several formats are commonly used
but all rely on plotting atoms in 3
dimensional space; .pdb is one of the
most popular.
Very Large Molecules
http://info.bio.cmu.edu/courses/03231/ProtStruc/ProtStruc.htm
B-DNA: Size, Shape & Self Assembly
Rosalind Franklin’s
Photo
46 Å
12 base sequence
(1953-2003)
http://molvis.sdsc.edu/pdb/dna_b_form.pdb
Atomic Orbitals
s and p orbitals
Molecular Orbitals
• Atomic orbitals mix to form molecular orbitals
•The total number of molecular orbitals
(bonding + non- and anti bonding orbitals)
equal the total number of atomic orbitals
s bond is formed by overlapping of two s
orbitals
In-phase overlap of s atomic orbitals form
a bonding MO (no node);
Out-of-phase overlap forms an antibonding MO (has node)
A single bond is a s bond with a bond order of 1.
A sigma bond (s) is also formed by end-on overlap
of two p orbitals
Double bonds have 1 s and 1 p bond with a bond order of 2.
A p bond is weaker than a s bond.
A double bond is shorter and stronger than a single bond.
Pi bond (p) is formed by sideways overlap of two parallel
p orbitals
Mixing Atomic Orbitals
Hybridization of s and p orbitals
Single Bonds (Methane)
Hybridization of s and p atomic orbitals:
http://chemconnections.org/organic/Movies%20Org%20Flash/HybridizationofCarbon.swf
The atomic orbitals used in bond formation
determine the bond angles
• Tetrahedral bond angle: 109.5°
• Electron pairs spread themselves into space as far from
each other as possible
Hybrid Orbitals of Ethane
Bonding in Ethene: A Double Bond
Double bonds have 1 pand 1 s bond.
A double bond is shorter and stronger than a single bond.
http://chemconnections.org/organic/Movies%20Org%20Flash/HybridizationofCarbon.swf
An sp2-Hybridized Carbon
• The bond angle in the sp2 carbon is 120°
• The sp2 carbon is the trigonal planar carbon
http://chemconnections.org/organic/Movies%20Org%20Flash/HybridizationofCarbon.swf
Ethyne: A Triple Bond
sp-Hybridized Carbon
• A triple bond consists of one s bond and two p bonds
with a bond order of 3.
•Triple bonds are shorter and stronger than double bonds
• There is a bond angle of the sp carbon: 180°
Question 18
• What is the molecular shape of each of the
carbons of tetrachloro ethene (Cl2CCCl2)?
•
A)
tetrahedral
•
B)
bent
•
C)
trigonal planar
•
D)
linear
•
E) trigonal pyramidal
http://chemconnections.org//organic/Movies Org Flash/hybridization.swf
Summary
• A p bond is weaker than a s bond
• The greater the electron density in the region of orbital
overlap, the stronger is the bond
• The more s character, the shorter and stronger is the
bond
• The more s character, the larger is the bond angle
Reactive Intermediates
Carbocation
Reactive Intermediates
Radical
Reactive Intermediates
Carbanion