A Brief Review
Organic Chemistry – study of
• Bonds with
• > million compounds
Bonding -- 2 ways to achieve
1. Ionic bond
Na
Ex:
+
Cl
Æ
H
Æ
2. Covalent bond
H
Ex:
+
Lewis Structures (molecules/ions): dots =
lines =
Common Bonding Patterns
Bonds
Lone prs.
Patterns
Ex:
Carbon
4
0
Nitrogen
3
1
Oxygen
2
2
Hydrogen
1
0
Halogen
1
3
Draw the Lewis structure for CH3CN
Formal charge: to determine charge on atom or polyatomic ion
F.C. = # valence e- in neutral atom – (all unshared e- + ½ shared e-)
Ex:
Determine which atom bears the charge on H3O+
Summer Notes
CHE 261
Chpt. 1,2 – pg. 1
Nonpolar
Covalent Bonds
Polar
Electronegativity -- Measure of
See Figure 1-6
∆EN = 0.5 – 1.9 Æ
Dipole moment – (
) defined as
C—H
Ex:
O—H
C — Cl
Note: Polarity of Molecule depends on
Resonance -- when single
•
Valence e-
Ex: Acetate ion (CH3CO2-) Æ 2 possible Lewis Structures
Contributing structuresÆ
Major
Minor
Resonance hybridÆ
Summer Notes
CHE 261
Chpt. 1,2 – pg. 2
Writing Organic Compounds
Compound
Lewis
Condensed
Line-angle
ethane
pentane
acetone
cyclohexanol
Acids & Bases
Bronsted-Lowry: Acids Æ
Bases Æ
HCl
+
NaOH
Æ
Strong
Weak
Strength measured by:
HA
Summer Notes
+
H2O
CHE 261
Chpt. 1,2 – pg. 3
Ka =
pKa =
pKa
acid strength
**Stronger acid Æ
**Acid-base reactions Æ
What about bases?
Acidity of Organic Acids Æ
4 main factors:
1. Electronegativity of atom bonded to acidic H
• More EN Æ
Ex:
H3C—H
HO—H
2. Size of atom bonded to acidic H
• Bigger Æ
Ex:
HI
HF
3. Resonance
• Is conjugate base
Ex: CH3CH2OH (ethanol)
pKa = 15.9
Summer Notes
CH3COOH (acetic acid)
pKa = 4.76
CHE 261
Chpt. 1,2 – pg. 4
4. Inductive Effect
• Positive charge withdraws e- from H—A bond Æ
O
H3C
C
O
H
Acids & Bases Take 2
Acid Æ
Base Æ
Lewis:
+
A
A
B
B
H
H
N
H
+
H+
H
H
N
H
H
Curved arrows Æ
End of Chpt. 1
Shapes of Molecules Æ
Valence Shell Electron Pair Repulsion Theory (VSEPR)
• Valence e- repel ∴
• Unshared e- repel
H
Ex:
CH4 (methane)
H
C
H
C
H
H
H
H
Summer Notes
CHE 261
H
Chpt. 1,2 – pg. 5
Ex:
H
NH3
N
H
N
H
H
H
H
Lewis Structures only predict shape Æ
Bonding: Sharing e- by
Sigma (σ) bond –
H
– overlap along bonding axis
+
H
1s
Æ
1s
H
H
sigma bond
C, N, O Æ also use p
Hybridization: sp3, sp2, sp
Hybridization
s+p+p+pÆ
Hybridized orbital
Example
CH4
s+p+pÆ
CH2CH2
s+pÆ
C2H2
Pi (π) bond Æ sharing of e- by
Æ double bond Æ
*Bond length: triple<
Summer Notes
CHE 261
Chpt. 1,2 – pg. 6
Summary Hybridization
# bonding
“areas”
4
3
Hybridization
Bond Types
Angles*
4 – sigma
3 – sigma
1 – pi
2 – sigma
2 – pi
109.5°
120°
2
180°
*
Ex: Determine the hybridization and bond angles and label the bond types for
hydrogen cyanide (HCN).
Single bonds – allow
Æ lots of
Double bonds –
Æ results in
Isomer
Constitutional
Isomer
Stereoisomer
Geometric
Def:
Summer Notes
Others
CHE 261
Chpt. 1,2 – pg. 7
Ex:
C4H10
2-butene
Molecular dipole moment Æ is the molecule
Must consider
&
Ex:
CCl4
CHCl3
Why important?
Types of Intermolecular Interations:
1.
dipole-dipole
Ex:
2.
CH4
b. pt. =
CH3OH
b. pt. =
London dispersion (
Ex:
Summer Notes
)
CHCl3
b. pt. =
CCl4
b. pt. =
CHE 261
Chpt. 1,2 – pg. 8
3.
Hydrogen bonding
Ex:
CH3OCH3
b. pt. =
CH3CH2OH
b. pt. =
Solubility Æ “
Ex:
“
Salt + water
Salt + gasoline
Wax + gasoline
Wax + water
Functional Groups
Æ Have specific
Æ Gives compound
H
H
H
C
C
H
H
H
Alkane (not true F.G.)
C
C
C
Alkene
C
Alkyne
OH
C
Arene
Summer Notes
Phenol
CHE 261
O
Alcohol
Chpt. 1,2 – pg. 9
H
C
C
S
H
C
Thiol
N
C
O
Ether
Amine
These groups contain a Carbonyl Group (not a functional group):
O
O
C
C
O
C
C
C
OH
H
Aldehyde
Ketone
O
C
Carboxylic Acid
O
O
O
O
C
C
C
C
N
O
Ester
Amide
Acetic Anhydride
Examples:
O
OH
OH
O
NH2
O
Summer Notes
CHE 261
Chpt. 1,2 – pg. 10