Electrostatic Potential Maps Models that visually portray polarity

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/DC 1 • 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.

Question 12 • The molecular formula of morpholine is: • A) C 2 HNO • B) C 4 HNO • C) C 4 H 4 NO • D) C 4 H 5 NO • E) C 4 H 9 NO

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 (CH 3)2 CHCH 2 CHBr. CH 3 is • • A) B) • • C) D)

Question 15 Select the best condensed structural formula for the following bond-line structure: A. B. C. D. E. (CH 3)2 CHCH 2 COHOHCOH CH 3 CHCH 2 C(OH)2 CHO (CH 3)2 CHCH 2 C(OH)2 COH CH 3 CH 2 C(OH)2 CHO

Line Drawing and Ball & Stick 8. 16 Å (0. 816 nm) http: //chemconnections. org/organic/chem 226/Labs/Smell. Stereochem. 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?

Question 17 • How many constitutional alcohol isomers have the molecular formula C 4 H 10 O? • 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/chem 226/Labs/VSEPR/

Very Large Molecules: DNA http: //www. umass. edu/microbio/chime/beta/pe_alpha/atlas. htm Views & Algorithms 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/Prot. Struc. 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%20 Org%20 Flash/Hybridizationof. Carbon. 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%20 Org%20 Flash/Hybridizationof. Carbon. swf

An sp 2 -Hybridized Carbon • The bond angle in the sp 2 carbon is 120° • The sp 2 carbon is the trigonal planar carbon http: //chemconnections. org/organic/Movies%20 Org%20 Flash/Hybridizationof. Carbon. 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 (Cl 2 C CCl 2)? • 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