LSW F02
Exam 1
Drawing diagrams:
Wedge-dash diagrams:
Sawhorse:
CH3
25
LSW F02
Exam 1
Newman:
Sight directly along a bond in the system
1) First draw the dot to represent the front C.
2) Then draw a circle to represent the back C.
3) Arrange bonds symmetrically on dot
4) Arrange bonds symmetrically around circle
5) Attach the rest of the chain to the bonds
Try to change a wedge dash diagram to a Newman projection:
Sight down C1-C2
C2-C3
26
LSW F02
Exam 1
Cyclohexane chair structures
Draw 3 sets of parallel lines
1) Draw the middle 2 lines first.
(be sure they start and end at slightly different positions)
2) Draw a line up from the bottom line and down from the
upper line.
3) Connect the lines to complete the chair.
Now attach hydrogens:
4) Two at each bend
5) In the middle the vertical lines go into the ring.
Otherwise the lines go away from the ring.
6) The horizontal lines are at the opposite angle of the slanted
bond.
27
LSW F02
Exam 1
Conformation Terms:
Conformer
(Rotamer)
Eclipsed
Conformation
HH
HH
Staggered
Conformation
H
H
H
Anti
Gauche
Syn
Eclipsed
Conformation
28
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
LSW F02
Exam 1
Conformational Analysis Terms:
Conformational
Analysis:
Heteroatom
Steric strain
(Van der Waals)
Torsional strain
Dihedral angle (φ)
(Torsional angle)
X
29
Y
LSW F02
Exam 1
Conformations of Simple Molecules:
H
Methane:
H
H
H
Ethane: CH3-CH3 most important conformations
H
H
H
H
H
H
H
H
H
H
H
H
HH
H
H
Staggered
H
H
HH
H
H
H
Eclipsed
Propane: CH3-CH2-CH3
H
CH3
CH3
CH3H
H
STAGGERED
CH3
ECLIPSED
30
H
H
LSW F02
Exam 1
Butane: CH3-CH2-CH2-CH3
Anti
CH3
CH3
CH3
Gauche
CH3
CH3
CH3
CH3
CH3
CH3
Eclipsed
CH3
CH3
CH3
Syn
31
CH3
CH3
CH3
CH3
LSW F02
Exam 1
Conformational Analysis of butane
100
Energy
75
50
25
0
0
90
180
270
360
Degree of Rotation
CH3
CH3
H
H
H
H H
H
CH3
CH3
CH3
H
CH3
H
H H
CH3
CH3
H
H
HH
H
H
32
CH3
CH3
H
CH3
H
H
H
H
CH3
H
CH3
H
H
H
H
H
H
CH3
LSW F02
Exam 1
You try:
2,2,3-trimethylpentane rotation along C3-C4.
H
H
Me
H
Me
t-Bu
A
Me
Me
H
H
E
H
t-Bu
H
Me
Me
H
H
H
C
B
Me H
Me
H
H
H
t-Bu Me
t-Bu
Me
H
H
H
Me
H
Me
H
Me
H
t-Bu
Me
F
H
G
33
t-Bu
t-Bu
D
H
Me
Me
H
H
t-Bu
H
LSW F02
Exam 1
Ring systems:
Terms:
Heterocycle
Puckered
Chair
Boat
Ring
flipping
Axial
ax
ax
ax
Equatorial
eq
eq
ax
ax
ax
eq
eq
eq
eq
Strain
Angle
strain
Ring strain
versus
34
LSW F02
Exam 1
Effect of cyclohexane ring flip
on axial and equatorial hydrogens
a
a
a
b
b
b
b
a b
b
a
a
a
a
b
a
a
b
a
a
b
b
Information about cyclic compounds
They are stable- but it depends on ring size.
Members 3
4
5
6
Stability
Reasons
35
7
8
9 and
above
LSW F02
Exam 1
∆ HH2 for cyclopropane and propene
∆HH2 (kcal/mol)
Reaction
+ H2
#1
∆Hf
12.8
0.0
+ H2
#2
∆Hf
-24.8
4.9
0.0
C=C is 146
Bonds π =
-24.8
C-C is 83
σ=
36
LSW F02
Exam 1
Cyclohexane Rings
Which is more stable cis or trans 1,4-dimethylcyclohexane?
Cis
Trans
You try: Draw cis 1,2-dimethylcyclohexane.
Which is more stable?
What if position 1 was a t-butyl group?
37
LSW F02
Exam 1
You Try: 1-tert-butyl-3-methylcyclohexane
1. Draw the 4 chair conformations and match them to the provided ∆Hf
2. Then calculate the equilibrium constant, K, for the interconversion of
the two cis forms at 25oC.
R
∆Hf (1)
∆Hf (2)
∆Hf (3)
∆Hf (4)
∆Hc (H2 gas)
∆Hc (C graphite)
kcal/mol
1.987 cal/mol K
-38.16
-40.53
-44.41
-46.84
-68.0
-94.0
kJ/mol
8.314 J/mol K
-159.66
-169.58
-185.81
-195.98
-284.51
-393.3
38
LSW F02
Exam 1
Multicyclic compounds:
spirocyclic "has a "spirocenter
polycyclic
bicyclic, tricyclic, tetracyclic….
fused
bridged
Adamantane
Cubane
39
LSW F02
Exam 1
Heterocycles
Cyclic compounds that contain heteroatoms, (O,S,N esp)
Ring size
Suffix
OXYGEN
3
-irane
4
-etane
5
-olane
6
-ane
Name
Compound
O
O
O
O
O
O
Common
Name
SULFUR
Ethylene
Oxide
Propylene
Oxide
Tetrahydrofuran
Tetrahydropyran
Name
Compound
S
S
S
S
S
S
Common
Ethylene Propylene Tetrahydro- Tetrahydrot
Name
Sulfide
Sulfide
thiophene
hiopyran
xxxxxxxxxxx xxxxxxxx xxxxxxxxx xxxxxxxxxxx xxxxxxxxxx xxxxxxxxx
NITROGEN
Name
Aziridine
Azetidine
H
Compound
N
Pyrrolidine
H
N
Piperidine
H
H
N
N
Morpholine
H
N
O
40