1. CHE2060 2: Simple Structures, Functional Groups
Topics
Drawing molecular structures
Arrow formalism & molecular framework
Introduction to alkanes
Isomers
IUPAC naming of alkanes
Alkyl halides & cycloalkanes
Functional groups: where the action is
Alkenes: hydrocarbons with > one double bond
Alkynes: hydrocarbons with > one triple bond
Alkene isomers: who’s across that double bond?
Arenes
Organohalogens
Using molecular formulas
Daley & Daley, Chapter 2
Organic Nomenclature & Functional Groups

2. Who’s across that double bond?
Alkenes Isomers:
Who’s across that double bond?

3. configurational isomers conformational isomers
Types of isomers
Same formula
Different in some way
isomers
Same connectivity? no
yes
constitutional isomers
stereoisomers
Different single bond rotation? no
yes
configurational isomers
conformational isomers
mirror images? no
yes
diastereomers
enantiomers
& cis-trans or E-Z
Karty p.177

4. Alkene steroisomers: cis vs. trans
Because there is no rotation around double bonds, alkenes can form stereoisomers: substituents arranged differently on either side of the double bond.
cis
trans
The two identical substituents are on the same side of the double bond
The two identical substituents are on the opposite sides of the double bond
cis-2-butene
trans-2-butene
Try cis-3-methyl-2-hexene.
D&D, p.107-9

5. Retinal: cis-trans detection of light
The retinal of the eye is exposed to light, detects that light, & transmits a signal (“light right there”) to the brain via the optic nerve. Retinal is the molecule responsible for detecting light and starting the signaling process.
Exposure to light converts 11-cis-retinal to all trans-retinal.
H&P, p.13

6. Alkene carbons with non-identical groups?
Cis and trans can be used to describe isomers only when each of the double bonded carbons share at least one substituent – like each has a methyl group.
What if all four substituents are different?
Identify the highest atomic mass atoms attached to each of the two double bonded carbons.
Determine whether the high mass atoms are on the same or opposite sides.
Zussamen
Entgegen
High mass on the same side of the double bond
High mass on the opposite side of the double bond
E-4-ethyl-6,7-dimethyl-4-nonene
E-3-cyclopentane-2-hexene
D&D, p.107-9