Alkenes 1

ShapeAlkenes, 6 coplanar atoms.

All atoms in same plane except for

these hydrogens on sp3 carbon.

Arene shapesPlanar ring structure. 12 atoms coplanar.

2-phenyl propane

Phenyl group, C6H5,, Ph

Ph

Ph = C6H5

Pi bonds

pi orbitalsum

pi* orbitaldifference

Ene

rgy

Nomenclature

but-1-ene 3,4-dimethylhexa-1,5-diene

cis / trans

cis trans

Z / E generalization of cis / trans

Use R, S priorities to compare substituents on same carbon.

High priority on same side, Z. Opposite, E.

H Br

FCl

H F

BrCl

(E)-1-bromo-2-chloro-1-fluoroethene(Z)-1-bromo-2-chloro-1-fluoroethene

Cis / Trans in CycloalkenesFor 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).

This moleculehas additional cross links.

Note that location of functional groups such as OH or double bonds is not addressed.

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 triglyceridetriglyceride.– Hydrolysis of a triglyceride in aqueous base followed by

acidification gives glycerol and three fatty acids.

– Fatty acids with no C=C double bonds are called saturated fatty acid.

– Those with one or more C=C double bonds are called unsaturated fatty acids.

CH2OCR

CH2OCR''

R'COCHO

O

1. NaOH, H2O

2. HCl, H2O

CH2OH

CH2OH

HOCH

RCOOH

R'COOH

R''COOH

+

Fatty acids

O

1,2,3-Propanetriol(glycerol)

A triglyceride(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 oilsoils.

– Triglycerides rich in saturated fatty acids are generally semisolids or solids at room temperature and are called fatsfats.

Fatty Acids

– the four most abundant fatty acidsCOOH

COOH

COOH

COOH

Stearic acid (18:0)(mp 70°C)

Oleic acid (18;1)(mp 16°C)

Linoleic acid (18:2)(mp-5°C)

Linolenic acid (18:3)(mp -11°C)