introduction and revie · lewis structures bonding electrons nonbonding electrons or lone pairs...
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Introduction and Review
lectuer 1 ..Assist.Prof.Dr.Mohanad Mousa Kareem 1
Organic Chemistry, 5th Edition
L. G. Wade, Jr.
ORGANIC CHEMISTRY
lectuer 1 ..Assist.Prof.Dr.Mohanad Mousa Kareem 2
STUDY OF CARBON-CONTAINING COMPOUNDS
lectuer 1 ..Assist.Prof.Dr.Mohanad Mousa Kareem 3
Classification of Matter
FIRE AGE - BASED ON COMBUSTION
COMBUSTIBLES - FUELS FROM ANIMALS AND PLANTS
OIL, WOOD, FAT
NON-COMBUSTIBLES -DIDNÕT BURN; PUT OUT FIRES
SAND, WATER, ROCKS
CLASSIFICATION OF MATTER
lectuer 1 ..Assist.Prof.Dr.Mohanad Mousa Kareem 4
BERZILIUS’ DEFINITIONS
ORGANIC COMPOUNDS
CHARACTERISTIC PRODUCTS OF LIVING ORGANISMS
SUBSTANCES LIKE SUGAR AND OLIVE OIL
INORGANIC COMPOUNDS
PRODUCTS FROM NON-LIVING ENVIRONMENT
SUBSTANCES LIKE WATER AND IRON
lectuer 1 ..Assist.Prof.Dr.Mohanad Mousa Kareem 5
Vital Force Theory
INORGANIC MATERIALS COULD BE CONVERTED
TO ORGANIC MATERIALS IN THE PRESENCE OF A
VITAL FORCE FOUND ONLY IN LIVING BODIES.
Woehler’s urea synthesis
lectuer 1 ..Assist.Prof.Dr.Mohanad Mousa Kareem 6
Ammonium isocyanate + heat ------> urea
NH4CNONH2CONH2
“I have been able to make urea without aid of kidney
of man or dog.
1828
lectuer 1 ..Assist.Prof.Dr.Mohanad Mousa Kareem 7
Post 1828
•Over 18,000 million compounds have been synthesized
•Pharmaceuticals
•Biochemicals
•Plastics
•Agrichemicals
•Paints
lectuer 1 ..Assist.Prof.Dr.Mohanad Mousa Kareem 8
Why so many organic?
H O N X P S Se
FORMS COVALENT BONDS WITH MANY METALS
Li Mg Al Cd Fe
FORMS COVALENT BONDS WITH NON-METALS
lectuer 1 ..Assist.Prof.Dr.Mohanad Mousa Kareem 9
AND
WITH ITSELF
CC
CC
C
CHAINS
CCH
CCH
C
CHAINS WITH BRANCHES
CC
C
C
C
C
C
C
RINGS
No limit
Atomic Structure
protons, neutrons, and electrons
isotopes
lectuer 1 ..Assist.Prof.Dr.Mohanad Mousa Kareem 10
C12
6 6C
14
=>
Atomic Orbitals
lectuer 1 ..Assist.Prof.Dr.Mohanad Mousa Kareem 11
2s orbital (spherical)
2p orbital =>
Electronic Configurations
Aufbau principle:
Place electrons
in lowest energy
orbital first.
Hund’s rule:
Equal energy
orbitals are half-
filled, then
filled.lectuer 1 ..Assist.Prof.Dr.Mohanad Mousa Kareem 12
=>
Table 1-1
lectuer 1 ..Assist.Prof.Dr.Mohanad Mousa Kareem 13 =>
Bond Formation
Ionic bonding: electrons are transferred.
Covalent bonding: electron pair is shared.
lectuer 1 ..Assist.Prof.Dr.Mohanad Mousa Kareem 14
=>
Lewis Structures
Bonding electrons
Nonbonding electrons or lone pairs
lectuer 1 ..Assist.Prof.Dr.Mohanad Mousa Kareem 15
Satisfy the octet rule! =>
C
H
H
H
OH
The octet rule is a chemical rule of thumb that reflects
observation that atoms of main-group elements tend to
combine in such a way that each atom has eight electrons in
its valence shell, giving it the same electronic configuration as
a noble gas.
TIPS
Neutral atoms
Carbon 4 bonds (double bonds count as 2 triple bonds count as 3) and NO lone pairs.
Nitrogen 3 bonds and one lone pair
Oxygen 2 bonds and two lone pairs
BORON 3 bonds BUT no lone pairs
lectuer 1 ..Assist.Prof.Dr.Mohanad Mousa Kareem 16
lectuer 1 ..Assist.Prof.Dr.Mohanad Mousa Kareem 17
TIPS2
C H-H+
CH- -
C+
N H-H+
N+H+
N HH+
O
H-H+
O+H+
O
H+
H
Multiple Bonding
lectuer 1 ..Assist.Prof.Dr.Mohanad Mousa Kareem 18
=>
EXAMPLES
lectuer 1 ..Assist.Prof.Dr.Mohanad Mousa Kareem 19
CO2SO2 C2H3N
C3H6O isomer problem
Dipole Moment
Amount of electrical charge x bond length.
Charge separation shown by electrostatic potential map (EPM).
Red indicates a partially negative region and blue indicates a partially positive region.
lectuer 1 ..Assist.Prof.Dr.Mohanad Mousa Kareem 20
C CH
H H
H
=>
Electronegativity and Bond
Polarity
Greater EN means greater polarity
lectuer 1 ..Assist.Prof.Dr.Mohanad Mousa Kareem 21=>
lectuer 1 ..Assist.Prof.Dr.Mohanad Mousa Kareem 22
EXAMPLES OF BOND POLARITY
C------BrC-------Li
C-------NBr--------Cl
Calculating Formal Charge
For each atom in a valid Lewis structure:
Count the number of valence electrons
Subtract all its nonbonding electrons
Subtract half of its bonding electrons
lectuer 1 ..Assist.Prof.Dr.Mohanad Mousa Kareem 23
C
H
H
H
C
O
O P
O
OO
O
3-
=>
Ionic Structures
lectuer 1 ..Assist.Prof.Dr.Mohanad Mousa Kareem 24
C
H
H
H N
H
H
H
+
Cl-
Na O CH3 or O CH3Na+
_
X
=>
Consider writing Lewis structure for NO3-2
The real structure is a resonance hybrid. All the bond lengths are the same. Each oxygen has a -1/3 electrical charge.
=>
lectuer 1 ..Assist.Prof.Dr.Mohanad Mousa Kareem 25
N
O
OO
_ _
N
O
OO
_
N
O
OO
Resonance - More than one
Lewis Diagram
lectuer 1 ..Assist.Prof.Dr.Mohanad Mousa Kareem 26
Resonance Rules
Must be legitimate Lewis structures
N
CH3
H3C
CH3
CH2+
-
N
CH3
H3C
CH3
CH2
NO NO Pentavalent nitrogen atom!!
Resonance structures?
lectuer 1 ..Assist.Prof.Dr.Mohanad Mousa Kareem 27
N
O
O
: N
O
O
:
OK
C
H
H
H
O
H
C
H
HOH
H
NO NO
Only electrons can be moved (usually lone pairs or pi electrons).
lectuer 1 ..Assist.Prof.Dr.Mohanad Mousa Kareem 28
Nuclei positions and bond angles remain the same.
C=C-C+ +C-C=C
The number of unpaired electrons remains the same
H3C CH3
..H3C CH3
. .
NO NO
lectuer 1 ..Assist.Prof.Dr.Mohanad Mousa Kareem 29
DELOCALIZATION OF CHARGE
USUALLY IS STABILIZING
Delocalization of charge results in fractional charges
at alternate atoms
Major Resonance Form
has as many octets as possible.
has as many bonds as possible.
has the negative charge on the most electronegative
atom.
has as little charge separation as possible.
lectuer 1 ..Assist.Prof.Dr.Mohanad Mousa Kareem 30
Example=>
Major Contributor?
lectuer 1 ..Assist.Prof.Dr.Mohanad Mousa Kareem 31
C
H
H
N
H
H
+C
H
H
N
H
H
+
major minor,
carbon does
not have octet.
=>
Chemical Formulas
Full structural formula (no lone pairs shown)
Line-angle formula
Condensed structural formula
Molecular formula
Empirical formula
CH3COOH
C2H4O2
CH2O =>
lectuer 1 ..Assist.Prof.Dr.Mohanad Mousa Kareem 32
C
H
H
H
C
O
O H
OH
O
BrØnsted-Lowry Acids
and Bases
Acids can donate a proton.
Bases can accept a proton.
Conjugate acid-base pairs.
lectuer 1 ..Assist.Prof.Dr.Mohanad Mousa Kareem 33
CH3 C
O
OH + CH3 NH2 CH3 C
O
O-
+ CH3 NH3+
=>
acid base conjugate
base
conjugate
acid
lectuer 1 ..Assist.Prof.Dr.Mohanad Mousa Kareem 34
EXAMPLES
CH3CO2H+ :NH3 CH3CO2
- + NH4+
ACID
BASE
CONJ BASE
CONJ ACID
H3C
O:
OH
+ H2SO4H3C
OH
OH
++ -HSO4
Amphoterism - ability to behave as an acid or base
Acid and Base Strength
Acid dissociation constant, Ka
Base dissociation constant, Kb
For conjugate pairs, (Ka)(Kb) = Kw
Spontaneous acid-base reactions proceed from stronger to weaker.
lectuer 1 ..Assist.Prof.Dr.Mohanad Mousa Kareem 35
CH3 C
O
OH + CH3 NH2 CH3 C
O
O-
+ CH3 NH3+
pKa 4.74 pKb 3.36 pKb 9.26 pKa 10.64
=>
lectuer 1 ..Assist.Prof.Dr.Mohanad Mousa Kareem 36
EXAMPLES
Will NaOH neutralize phenol (C6H5OH)?
NaOH +
C6H5OH
HOH+
C6H5ONa
pKa = 10 pKa = 15.7
_-OH
C6H5OH
HOH + C6H5O-+
YES!!
Weaker acidStronger acid
Determining Relative Acidity
Electronegativity
Size
Resonance stabilization of conjugate base
=>
lectuer 1 ..Assist.Prof.Dr.Mohanad Mousa Kareem 37
Electronegativity
As the bond to H becomes more polarized, H becomes more positive and
the bond is easier to break.
lectuer 1 ..Assist.Prof.Dr.Mohanad Mousa Kareem 38
=>
Size
As size increases, the H is more loosely held and the bond is easier to break.
A larger size also stabilizes the anion.
lectuer 1 ..Assist.Prof.Dr.Mohanad Mousa Kareem 39
=>
Resonance
Delocalization of the negative charge on the conjugate base will stabilize the anion, so the substance is a stronger acid.
More resonance structures usually mean greater stabilization.
lectuer 1 ..Assist.Prof.Dr.Mohanad Mousa Kareem 40
CH3CH2OH < CH3C
O
OH < CH3 S
O
O
OH
=>
Lewis Acids and Bases
Acids accept electron pairs = electrophile
Bases donate electron pairs = nucleophile
lectuer 1 ..Assist.Prof.Dr.Mohanad Mousa Kareem 41
CH2 CH2 + BF3 BF3 CH2 CH2+_
nucleophile electrophile
=>