Topic 5: Alkenes pt 2

Question 1

The Structure of Alkenes

Answer 1

Rotation breaks the π bond

Question 2

Cis-Trans Isomerism

Answer 2

In alkenes,
If they are pointing the same direction then they are cis to one another.

If you have 2 substituents on the opposite directions, they are trans to each other.

Question 3

The E, Z System of Nomenclature

Answer 3

Using cis & trans to name alkenes only works if you have one hydrogen on each of the alkene carbons… if you dont then you have to use a system called the E/Z naming convention.

Question 4

The E, Z System of Nomeclature

Answer 4

High priority on the same side= Z (zusammen… together)

High and Low priority across from one another = E (entgegen…across)

How do you determine a substituent priority?

Question 5

CAHN, INGOLD, PRELOG SEQUENCE RULES FOR E& Z NOMECLATURE (Step 1)

Answer 5

Step 1: First prioritize the groups bonded to the 2 sp2 carbons.
(Relative properties depend first on the atomic # of the atom… not the formula weight of the group) bonded to sp2.

Question 6

CAHN, INGOLD, PRELOG SEQUENCE RULES FOR E& Z NOMECLATURE (Step 2)

Answer 6

Step 2: In the case of a tie, the atomic # of the atoms bonded to the tied atoms are considered next

Question 7

CAHN, INGOLD, PRELOG SEQUENCE RULES FOR E& Z NOMECLATURE (Step 3)

Answer 7

Step 3: If an atom is doubly bonded to another atom, the system creates if it were bonded to 2 such atoms

Question 8

CAHN, INGOLD, PRELOG SEQUENCE RULES FOR E& Z NOMECLATURE (Step 4)

Answer 8

Step 4: In the case of isotopes, the isotope with the greater mass # has the higher priority.

Step 5: If the groups of the highest priority are on the same side of the double bond, name the isomer Z (Zusammen)

Step 6: if the groups of highest priority are on the opposite side of the double bond, name the isomer E (Entgegen)