E-Z Notation Flashcards Preview

Chemistry 6 - Organic Chemistry > E-Z Notation > Flashcards

Flashcards in E-Z Notation Deck (18)
1

what is the problem that comes with using the cis-trans notation

it only works for some compounds

2

why doesnt the cis-trans notation work with:
H Cl H Br
| | | |
C=C C=C
| | | |
F Br F Cl

- there are 4 different groups
- so the idea of two identical groups being in a cis-trans relationship doesnt work
- as there are not two groups that are the same

3

what system would we use instead rather then cis-trans notation

the E-Z system

4

what is the first step when using the E-Z system

- work out the part of the name that can be used for both isomers
- by using the normal nomenclature rules

5

what would the common name between these two isomers

1-bromo-1-chloro-2-floroethene

6

what is the second step in the system

using the priority rules to decide which of the two toms on the left hand side of the double bond has higher priority

7

how is priority decided in this case

- it is decided by the atom with the higher atomic number
- H=1 and F=9
- so F has the higher priority

8

what is step 3

- do the same thing for the atoms on the right hand side of the double bond
- Cl = 17 and Br = 35
- so Br has higher priority

9

what is the final step of the E-Z system

decide whether the two higher priority atoms are at opposite ends if the molecule (across and up / down) or not

10

what kind of isomer do you have if the higher priority atoms are at opposite ends of each other

an E-isomer (equivalent of trans)

11

what kind of isomer do you have if the higher priority atoms are at opposite sides but no opposite ends of each other

a Z-isomer (equivalent of cis)

12

what would be the isomer of the first and second molecule previously shown

- the first one would be a Z-isomer
- the second would be an E-isomer
- as in the first the F and Br are only at opposite sides
- whereas in the second they are are opposite ends

13

what is a way of remembering the difference between E and Z isomer

- the E in E-isomer stands for enemy
- as the high priority atoms are enemies with each other
- ans therefore want to stay as far away from each other as possible
- so they would be at opposite ends
- Z-isomers are just the other option

14

where do the letters E and Z come from in the first place

- the letter E used comes from the german word entegen
- which means opposite
- the letter Z used comes from the german word zusammen
- which means together (opposite sides but shoulders touching kinda thing)

15

what is the definition of structural isomer

- compounds with the same molecular formula
- but with different structural formulae

16

what is the definition of a stereoisomer

- compounds with the same molecular and structural formula
- but with a different arrangement of atoms or groups in a 3 dimensional field

17

what is the definition of a geometric isomer

- compounds containing a C=C bond
- with atoms or groups attached at different positions

18

what is the definition of restricted rotation

when the atoms or groups bonded to a C=C bond have their postions fixed