1
4 Identifying Formal Charges
What is a Formal
change
Identifying
charge
a
Formal
FormalCharge
Any atom thatdoesn'texhibit the appropriate
of valenceelectrons
1 Determine the appropriate
ofvalence electrons for
Check periodic table
the'itomistibits theapitipriate
2 DetermineEither
Example
ft
O
H
I
C
I
H
H
H
c
H
Practice 1.7
1
D 5VE
H I VE
H
t.lt
it
H I VE
2 a
A 3 VE
H
H
HEH
atom
of valence electrons
appropriate
group
an
eu iah oitIy
p
H
H
1
C
1
H
H
ofelectron
H lVE
0 6VE
b
d
O
H l VE
0 6V E
0
t
I
N 5 VE
III
e
4VE
YEE
E
EYV E
9
0
h
i
C
6 E
I IE
to
EYVE
0 6 E
N 5V E
Practice 1.8
a
Bit
H DEH
it
b NH
H
Celts
P
H
É
Yc
Practice 1.9
H
I VE
Polar Covalent
1.5 Induction
what
are
the 3 bond
categories
comesfrom the electronegativity values of theatom
1 Covalent
2 PolarCovalent sharing a bond
g g
Electronegativity Measure of
electrons
what is the difference
in the electronegativity
values of the 2 atoms
Bonds
the ability of an atom to attract
Guidelines
Covalentbond
Ex
If difference in electronegativity is
PolarCovalent
0.5
Is
If difference in electronegativity is between
0.5 1.7
Ex
Induction the withdrawal of electrons toward the
lesselectronegative atom
symbol
grggibal
Ionic band If
Ex
difference in electronegativity is
3.5
1.7
09 5
ocating Partial Charges Identify all polar covalent bonds show any partial
Resultingfrom Induction charges that result from inductive effects
step 1
Identify all polarcovalent bonds
is
f
ya
Step 2 Determine the direction of each dipole
Step 3 Indicate the location of partialcharges
2 1 Molecular Representations
Different Representations
Practice 2.1
Draw a Lewisstructure
a
for each of the
H.CCHOCH.CHcH3
a
H H
L
H
Y
E
EEE H C H
H
b CHCH CHCH.CH OH
tt I
compound
C CH CH Colt
H
ÉÉÉÉ
I HH G H
H H
E
Practice 2.2
Ecco
a HOCH CH CH CHO
I
c
go
a
É
c CHzCOzCHzCHz
Hiiiii e É É it
Practice 2.3
Identify the
to
Esp
of sp hybridized carbon atoms
É3
H
H
y't't
2.2 Bond Line Structures
what are therules to
ravingbond line
fractures
Bond time structures Rules
1 Carbon atoms in a straight chain should be drawn in a
zigzag format
2 When drawing doublebonds draw all bands as far as possible
3 Whendrawingsingle bonds the direction in which the bond
are
drawn is irrelevant
4 Allheteroatoms atomsotherthan C and H mustbe drawn
andany H atoms attached to a heteroatom mustalso
be drawn
5Never draw a C atom w more than 4 bands Carbons
onlyhas 4 orbitals in its valence shell and therefore C
atoms can
form
a maximum
of 4 bonds
Practice 2.2 Drawing Band Line Structures
Step 1 Delete It atoms except for thoseconnected to
heteroatoms
step 2
Draw in zigzag format keeping triple bands
linear
Step 3 Delete carbon
atoms
Practice 2.4
b
a
Q
c
O
g
Practice
a
2.5
fit CCCHs
H
H
EH
HH
É Yd d É it
I it it it it
g g
D CH CA CH CH
i
C
i
CH CHz COH
cittjitis
it
d CH CHCH OH
HI HH
H E
fH
H
E
H
o H
Practice 2.6
CHCH CH
É.IE
It
CHCH
EtEt
It it it it d it
it
z
2.3 Identifying Functional Groups
what is a functional
group
group A characteristic group of atoms bonds
Functional
that possess
a
predictable chemical behavior
R refers to the remainder
of the compound usuallycarbon
and hydrogen atoms
2.7 Introduction to Resonance
hat is Resonance
Resonance stabilization
Resonance The approach that chemists use to deal w the
inadequacy of bond line structures
Drawmore than I bond line structure then mentally meld them
together
q
ft
Delocalization Stabilizing factor
2T electrons are spread out over
3C
atoms
of the allylicsystem
Resonance Structure
Resonance stabilization molecules
andions are stabilized by the
delocalization of electrons
2.8 Curved
what are curved arrows
Arrows
Curved Arrows tools necessary to draw resonance structures
properly
They don'trepresent the motion ofelectrons
where electrons
the
arecomingfrom
shots
where theelectrons
shows
therules for
arrows for
curved
raving
what
are
esonance structures
are going
Rules for drawing carved
arrows
1 Avoid breaking a single bond
2 Neverexceed
an
for resonance structures
octet for 2nd row elements
The violation is difficult to see in bondline structures
Not a violation if
an
a
2nd
octet of electrons
row element
has less than
Prentice 2.5 Identifying valid Resonance arrows
Determine whether it violates either of the two rules
for drawing curved arrows
step1 it doesn'tbreak a single bond
step 2 Ctonlyhas 3 bands not 4 Thecurved arrow will
give the
The arrow is correct
Practice 2.12
a
Catom
a
4th bond
5.1 Overview of Isomerism
what are isomers
Isomers
Compounds
that
are constructed from
the same
atoms same molecular formula
differ in the connectivity
of their atoms
same molecular formula
differ
in theirconstitution different
compounds w different physical
properties
same constitution
differ
in the spatialarrangement of
theiratoms
5.1 Practice
translepp side
H
this is not a stereoisomer
Iistsg.ge E ble of this
trans cis needs to attach to diff groups
5.2 Practice
AM
I
YAY't
H
H
since both double bonds
are
attached
to the same
group neither one is
are
stereoisomers
5.3 Practice
I
b
gag
trans stereoisomer
chometyoups
a stereoisomer
gt
TEFastereoisomer
a
stereoisomer
stereoisomer
5.2
Intro
to
Stereoisomerism
Chiral objects that aren't superimposable on their
Molecular Chirality
mirror
images
1996 IUPAC re ommended that a tetrahedral carbon
bearing 4 diff groups be called chirality center
From now on
we'll
use
chiralcenter
ÉEF
bond sooner
No chiral center
tow to locate chiral
centers
step Ignore sp and sp hybridized carbon atoms
Remember
Groups
Hybridization
Ipp
Step2 Ignore Clt and Cfs groups
P
Step 3 Identify any carbon atoms bearing 4
different groups
Enatiomers
when
compound is chiral it will have one
nonsuperimposable mirror image called its
a
enantiomer
The compound and its mirror image are said
to be
pair of enantiomers
A chiral compound will have exactly ONE
a
enantiomers
Drawing An Enantiomer
There are 3 places
1 Behind
2 Next to
3 Beneath
side
side
Behind
beneath
All produce
the same
answer
5.3 Designating Configuration Using the
Cahn Ingold Prolog system
ahn Ingold Prolog SystemStep 1
Assign priorities to each of the 4 groups attached
to the chiral center based on atomic number
Atom
w
priority
Atom
w
highest atomic
lowest atomic
priority 4
step 2
I
is assigned highest
is assigned lowest
Rotate molecule so that the 4th
the page on a dash
is
directed behind
Step 3
Then see if the l 2 3 sequence is clockwise or
counterclockwise
S counterclockwise
R Clockwise
Assigning
Priorities to All 4 Groups