Organic Chemistry Chapter 1 Summery
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CHAPTER #1: STRUCTURE and BONDING
ORGANIC CHEMISTRY
DEFINITIONS AND HISTORY
In the early 1800’s “organic molecules” came from an organism.
In 1828 Frederich Wohler synthesized urea (natural, organic) from ammonium cyanate (inorganic). Urea had never before been made “…without thereby needing to have kidneys…”
Elements in Human Body Elements in Dry Human Oxygen 65% Carbon 62% Carbon 18% Nitrogen 11%
Hydrogen 10% Oxygen 9% Nitrogen 3% Hydrogen 6% Calcium 1.5% Calcium 5%
C NOH N
H
H
H
C
O
N NH
H
H
H
heat
ammonium cyanate urea
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WHY CARBON?
ORGANIC CHEMISTRY TOPICS
Molecular Structure and Atomic Groupings
Ethyl alcohol (“alcohol”) Dimethyl ether (propellant)
Chemical Reactions
H C
H
H
C
H
H
O H H C
H
H
O C H
H
H
C
C C
C
C C C
O
O
O H
H
H
H
H
H
C
C C
C
C C C
O
O
O
H
H
H
H
H C O C
H
H H
C C O
O C C
O
H
H H
H
H H
salicylic acid acetylsalicylic acid
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LEWIS STRUCTURES
METHOD
1. Sum the valence electrons.
For each negative charge ____________________, for each positive charge ____________________.
2. Draw the skeleton (for complicated structures this may be given).
3. Use the valence electrons to give all atoms an octet (8 e–), except hydrogen which should have a duet (2 e–).
EXAMPLES
CH2O (Formaldehyde) CH3NH–
CH2NH2– CH2NH2+
NaCN (sodium cyanide)
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FORMAL CHARGE
METHOD
For each element apply this formula:
Formal Charge = (Valence electrons) – (Electrons “owned” by the element)
HONC PRINCIPLE
When neutral… H makes O makes N makes C makes
Anion Neutral Cation
HCONH– NO3–
+ H C
H
O H
H C
O
N H O N
O
O
Heme unit in hemoglobin
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RESONANCE STRUCTURES
REVIEW
CHO2–
Bond Lengths1
Labrador Poodle Carbonate bond lengths2
1 Allen, F.H., Kennard, O., J. Chem. Soc., Perkin Trans., 2, 1987, S1-S19 (follows p. 1914) 2 Solomons, G., Fryhle, C.B., Organic Chemistry, 8th ed., Wiley, 2004, pp. 15
H C
O
O
C
O
C
O H C
O
O
O
C O O
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RESONANCE
REASONABLE RESONANCE STRUCTURES
In “reasonable” resonance structures,
MAJOR AND MINOR CONTRIBUTORS
To follow are rules (in order of importance) for determining the major resonance contributor for a compound:
1. A resonance structure where all atoms have an octet contributes more than a resonance structure that lacks an octet (most important “rule”).
Electrostatic potential energy diagrams (color-coding electron density)3
3 Electrostatic potential energy diagrams in this chapter were generated by Lisa Nichols using WebMO, thanks to the Institute for Chemical Literacy through Computational Science.
C O C O OC O
C HH
O
C HH
C N
H
H H
H
H F
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2. A neutral resonance structure contributes more than one with charge, especially separated charge.
3. When all structures have octets and charge, the greatest contributor has the charge on the element with the appropriate electronegativity. a. A negative charge is best situated on the __________ electronegative atom.
b. A positive charge is best situated on the __________ electronegative atom.
H C
O
N
H
H
H C
O
N H
H C
O
N H
H
H
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MORE EXAMPLES
Draw all resonance structures, then rank in order from most important to least important to the overall resonance hybrid. Explain your answer.
(There are 5 total, but only draw 2 more)
RESONANCE AND ENERGY
C C
C N
H
H
H
H
H
C
C N
C
C
H
H H
H
H C
O
O H C
O
O H C
H
O
H
vs.
H C
O
O H C
O
O H C
O
C H C
O
CH
H
H
H
vs.
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COMMON POLYATOMIC IONS
MOLECULAR SHAPE (VSEPR)
e– groups around central atom
e– geometry
bond angles
central atom hybridization
O N
O
OO
N O O
O N
O
O
O N
O O N
O
O P
O
O
O
O
P O
O
O OP
O
O
O
O
PO
O
O
O C
O
OO
C O O
O C
O
O
O Mn
O
O
O
O
Mn O
O
O OMn
O
O
O
O
MnO
O
O
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HYBRIDIZATION AND ORBITAL DIAGRAMS
VALENCE BOND THEORY
Bonding in F2
sp3 HYBRIDIZATION
Ammonia angles4
4 Jones, M., Fleming, S.A., Organic Chemistry, 4th ed., Norton, 2010, pp. 252
H N
H
H orbital
diagram
H C
H
H
H
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sp2 HYBRIDIZATION
Ethylene angles5
sp HYBRIDIZATION
Total σ bonds: ________ π bonds: ________
5 Jones, M., Fleming, S.A., Organic Chemistry, 4th ed., Norton, 2010, pp. 46
O C H
C H
H H
H C
H
H
C C
C C H
H H
H
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SHAPE AND HYBRIDIZATION SUMMARY
1. Assuming hybridization of the oxygen atom, lone pair A is in what type of orbital?
2. List the orbitals on both carbon atoms used to form the sigma bond labeled B.
3. Estimate bond angle C.
4. List the orbitals on carbon and oxygen atoms used to form the σ and π bond in D. σ:
π:
5. What is the electron geometry of the atom labeled E?
6. What is the hybridization of the nitrogen atom?
7. List the orbitals used to make the σ bond labeled F.
C C C
H
H
C
H
H
C
O
H
C
H
H
OH
N
O
A
B C
D
E F