Alkenes 1
Shape
Alkenes, 6 coplanar atoms.
All atoms in same
plane except for
these hydrogens on
sp3 carbon.
Arene shapes
Planar ring structure. 12 atoms coplanar.
Phenyl group,
C6H5,, Ph
Ph
Ph = C6H5
2-phenyl propane
Pi bonds
pi* orbital
Energy
difference
pi orbital
sum
Nomenclature
but-1-ene
3,4-dimethylhexa-1,5-diene
Z / E generalization of cis / trans
Use R, S priorities to compare
substituents on same carbon.
cis / trans
High priority on same side, Z.
Opposite, E.
H
cis
Br
H
F
trans
Cl
F
Cl
Br
(E)-1-bromo-2-chloro-1-fluoroethene
(Z)-1-bromo-2-chloro-1-fluoroethene
Cis / Trans in Cycloalkenes
For small rings normally have cis double bonds.
trans cyclooctene
Terpenes and the isoprene Rule
• A terpene is composed of isoprene units
joined head to tail (the isoprene rule).
Note that location of
functional groups such as
OH or double bonds is not
addressed.
This
molecule
has
additional
cross
links.
Vitamin A
Four isprene units joined head to tail
One cross link (non-head to tail) linkage.
Fatty Acids
• Animal fats and vegetable oils are both
triesters of glycerol, hence the name
triglyceride.
– Hydrolysis of a triglyceride in aqueous base
followed by acidification gives glycerol and
three fatty acids.
O
RCOOH
CH2 OH
O CH 2 OCR
1 . Na OH, H 2 O
R'COCH
HOCH
+ R' COOH
O
2 . HCl, H 2 O
CH2 OH
CH 2 OCR' '
R' ' COOH
1,2,3-Propanetriol
Fatty acids
A triglyceride
(glycerol)
(a triester of glycerol
Fatty Acids
– The most common fatty acids have an even
number of carbons, and between 12 and 20
carbons in an unbranched chain.
– The C=C double bonds in almost all naturally
occurring fatty acids have a cis configuration.
– The greater degree of unsaturation, the lower
the melting point.
– Triglycerides rich in unsaturated fatty acids
are generally liquid at room temperature and
are called oils.
– Triglycerides rich in saturated fatty acids are
generally semisolids or solids at room
temperature and are called fats.
Fatty Acids
– the four most abundant fatty acids
COOH Stearic acid (18:0)
(mp 70°C)
COOH Oleic acid (18;1)
(mp 16°C)
COOH Linoleic acid (18:2)
(mp-5°C)
COOH Lin olen ic acid (18:3)
(mp -11°C)