When identical polar bonds point in opposite directions,the effects of their polaritiescancel, giving no net dipolemoment. When they do notpoint in opposite directions,there is a net effect and a netmolecular dipole moment,designated
Molecular Polarity Molecular Polarity & Dipole Moment& Dipole Moment
The vector sum of the magnitude and the direction of the individual bond dipole determines the overall dipole moment of a molecule
Molecular Dipole Moment
An electrically charged rod attracts a streamof chloroform buthas no effect on a stream of carbontetrachloride.
• Resultant Molecular Dipoles > 0• Solubility: Polar molecules that
dissolve or are dissolved in like molecules
Polarity & Physical PropertiesOzone and Water
• The Lotus flower• Water & dirt repellancy
0.1278 nm
The “Lotus Effect” Biomimicry
http://bfi.org/biomimicry
• Lotus petals have micrometer-scale roughness, resulting in water contact angles up to 170°
• See the Left image in the illustration on the right.
Wax
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.
1.
2.
3.
4.
ketone
O
1.
aldehyde
H
O
O
2.
NOT
carboxylic acid
C
O
O
H
C
O
2
H
O
H
O
or
or
3.
ester (carboxylic acid ester)
O
O
C
H
3
O
O
C
O
O
C
H
3
or
NOT
4.
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?
Select the best condensed structural formula for the following bond-line structure:
HHO OH
O
A. (CH3)2CHCH2COHOHCOH
B. CH3CH3CHCH2C(OH)2CHO
C. (CH3)2CHCH2C(OH)2CHO
D. (CH3)2CHCH2C(OH)2COH
E. CH3CHCH3CH2C(OH)2CHO
Question 15
Line Drawing and Ball & Stick
8.16 Å (0.816 nm)
http://chemconnections.org/organic/chem226/Labs/Smell/Smell-Stereochem.html
Question 16While on-line, click on the jmol-structure
on the left. Which one of the formulas or structural renderings that follow is correct?
C
H
3
C
H
2
O
H
C
H
2
C
O
O
H
C
H
3
O
O
H
O
H
O
C
2
H
3
O
B)
C)
D)
E)
A)
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 1http://chemconnections.org/organic/chem226/Labs/VSEPR/
Very Large Molecules:DNAhttp://www.umass.edu/microbio/chime/beta/pe_alpha/atlas/atlas.htm
Views & Algorithms
10.85 Å10.85 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 Moleculeshttp://info.bio.cmu.edu/courses/03231/ProtStruc/ProtStruc.htm
B-DNA: Size, Shape & Self Assembly
http://molvis.sdsc.edu/pdb/dna_b_form.pdb
46 Å
12 base sequence
(1953-2003)
Rosalind Franklin’sPhoto
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
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 bond with a bond order of 1.
A sigma bond () is also formed by end-on overlap of two p orbitals
Double bonds have 1 and 1 bond with a bond order of 2.A bond is weaker than a bond.A double bond is shorter and stronger than a single bond.
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
Bonding in Ethene: A Double Bond
Double bonds have 1 and 1 bond. A double bond is shorter and stronger than a single bond.
http://chemconnections.org/organic/Movies%20Org%20Flash/HybridizationofCarbon.swf
• The bond angle in the sp2 carbon is 120°
• The sp2 carbon is the trigonal planar carbon
An sp2-Hybridized Carbon
http://chemconnections.org/organic/Movies%20Org%20Flash/HybridizationofCarbon.swf
Ethyne: A Triple Bondsp-Hybridized Carbon
• A triple bond consists of one bond and two 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 (Cl2CCCl2)?
• A) tetrahedral• B) bent• C) trigonal planar• D) linear• E) trigonal pyramidal
http://chemconnections.org//organic/Movies Org Flash/hybridization.swf
Summary• A bond is weaker than a 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