Electrostatic Potential Maps
Hydrogen Halides
Models that visually portray polarity and dipoles
Molecular Dipole Moment
Molecular Polarity
& Dipole Moment
The vector sum of the magnitude and the direction of the individual
bond dipole determines the overall dipole moment of a molecule
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 δ.
Ammonia and in the Ammonium Ion
An electrically
charged rod
attracts a stream
of chloroform but
has no effect on a
stream of carbon
tetrachloride.
Polarity & Physical Properties
Water
Ozone and Water
0.1278 nm
•
•
The “Lotus Effect”
Biomimicry
Resultant Molecular Dipoles > 0
Solubility: Polar molecules that
dissolve or are dissolved in like
molecules
The “Lotus Effect”
http://www.sciencemag.org/cgi/content/full/299/5611/1377/DC1
•
•
•
The Lotus flower
Water & dirt repellancy
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.
•
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.
Question 12
ketone
1.
• The molecular formula of morpholine is:
•
A)
C2HNO
•
B)
C4HNO
•
C) C4H4NO
•
D) C4H5NO
•
E) C4H9NO
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
OCH3
or
NOT
O
CO2H
O
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
Question 14
• The bond-line representation for
(CH3)2CHCH2CH2CHBrCH3 is
•
•
A)
B)
•
•
C)
D)
Formulas &
Kekulé / Condensed / Bond-Line
Structures / Drawings
Empirical Formula?
Molecular formula?
Bond-Line Structure?
Question 15
Select the best condensed structural formula for
the following bond-line structure:
HO OH
H
O
A.
B.
C.
D.
E.
(CH3)2CHCH2 COHOHCOH
CH3CH3CHCH2 C(OH)2CHO
(CH3)2CHCH2 C(OH)2CHO
(CH3)2CHCH2 C(OH)2COH
CH3CHCH3 CH2 C(OH)2CHO
Question 16
Line Drawing and Ball & Stick
While on-line, click on the jmol-structure
on the left.
Which one of the formulas or
structural renderings that
follow is correct?
A)
8.16 Å (0.816 nm)
http://chemconnections.org/organic/chem226/Labs/Smell/SmellStereochem.html
C 2H3O
D)
O
B)
C)
H 3C
O
CH2 COOH
H
E)
CH3 CH 2 OH
O
OH
Question 17
• How many constitutional alcohol isomers
have the molecular formula C4H10O?
•
A) two
•
B) three
•
C) four
•
D) five
Very Large Molecules:DNA
More Molecular Representations
http://www.umass.edu/microbio/chime/beta/pe_alpha/atlas/atlas.htm
Views & Algorithms
Empirical Formula, Molecular Formula, Structure:
(Lewis, Kekule, Condensed, Line), Visual Model:
wireframe, stick, ball & stick, space filling,
electrostatic, energy surface
10.85 Å
Worksheet: Organic Molecules 1
http://chemconnections.org/organic/chem226/Labs/VSEPR/
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
Atomic Orbitals
s and p orbitals
46 Å
Rosalind Franklin’s
Photo
12 base sequence
(1953-2003)
http://molvis.sdsc.edu/pdb/dna_b_form.pdb
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
• Α σ 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 σ bond with a bond order of 1.
A sigma bond (σ) is also formed by end-on overlap
of two p orbitals
Double bonds have 1 σ and 1 π bond with a bond order of 2.
A π bond is weaker than a σ bond.
A double bond is shorter and stronger than a single bond.
Pi bond (π) is formed by sideways overlap of two parallel
p orbitals
Mixing Atomic Orbitals
Hybridization of s and p orbitals
Single Bonds (Methane)
The atomic orbitals used in bond formation
determine the bond angles
Hybridization of s and p atomic orbitals:
• Tetrahedral bond angle: 109.5°
http://chemconnections.org/organic/Movies%20Org%20Flash/HybridizationofCarbon.swf
• 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 π and 1 σ 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 σ bond and two π 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 π bond is weaker than a σ 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