4.1.1, 5.3.1 Isomerism

Question 1

Define structural isomers

Answer 1

structural isomers are compounds with the same molecular formula but different structual formulas

Question 2

Define isoelectronic

Answer 2

the same number of electrons

Question 3

define isomer

Answer 3

Isomers are compounds with the same molecular formula

Question 4

When do isomers exist in alkanes

Answer 4

when n ≥ 4

Question 5

When do isomers exist in alkenes

Answer 5

when n ≥ 4

Question 6

What can be present in structural isomers

Answer 6

Different functional groups

Question 7

what are the two structures of isomers

Answer 7

• straight chained
• branched

Question 8

What isomers can Alkenes form

Answer 8

Structural isomers and stereoisomers

Question 9

Define stereoisomers

Answer 9

Stereoisomers are compounds with the same structural formula (+ molecular formula) but different arrangement of atoms in space.

Question 10

Why can alkenes form stereoisomers

Answer 10

Alkenes can form stereoisomers because their is restricted rotation around the C=C bond.

Question 11

How can structural isomers be formed

Answer 11

By changing the position of the functional group and/or the branching of the carbon chain.

Question 12

what is the role of aldehydes and ketones in isomers

Answer 12

Sometimes two molecules containing different functional groups have the same molecular formula.

Question 13

what are the types of stereoisomerism

Answer 13

E/Z isomerism and as a subcatagory cis and trans isomerism

Question 14

define E/Z isomerism

Answer 14

E/Z isomerism is a type of stereoisomerism in which different groups attatched to each carbon of a C=C double bond may be arranged differently in space because of the restricted rotation of the C=C bond.

Question 15

define cis/trans isomerism

Answer 15

Is a special type of E/Z isomerism in which there are two non-hydrogen groups and two hydrogen atoms around the C=C bond.
The cis isomer (Z isomer) has H atoms on each carbon on the same side.
The trans isomer (E isomer) has H atoms on each carbon atoms on different sides.

Question 16

When do alkenes have E/Z stereoisomers

Answer 16

alkenes can have E/Z stereoisomers if there are two different groups on the C at each end if the alkene (each C of the double bond has two different groups attached)

Question 17

What conditions need to be met for a structure to be considered to have E/Z isomerism

Answer 17

• A C=C double bond
• different groups attatched to each carbon atom of the double bond

BOTH are required

Question 18

Explain why but-1-ene and but-2-ene are not both considered E/Z isomers

Answer 18

In But-1-ene, the carbon atom on one side of the molecule is attatched to two hydrogen atoms. This means that its structure does not satisfy the condition of different groups being attatched to each carbon of the C=C.
But-2-ene on the other hand has a methylgroup and a hydrogen atom on each of the carbon atoms in the double bond, so it has E and Z isomers.

Question 19

What requirements do cis/trans isomers require

Answer 19

In addition to the requirements of a E/Z isomer (as cis/trans is a subcatagory) one of the attached groups on each carbon atom of the double bond must be hydrogen

Question 20

how are cis/trans isomers and E/Z isomers connected

Answer 20

cis/trans isomerism is a special case of E/Z isomerism.
A cis isomer is of the Z isomer. It has the hydrogen atoms on each side of the C=C on the same side of the molecule.
A trans isomer is of the E isomer. It has the hydrogen atoms diagonally opposite each other.

Question 21

How are isomers labled E or Z

Answer 21

Through the Cahn-Ingot-Prelog rules:
In this system the atoms attatched to each carbon atom in a double bond are given a priority based upon their atomic number.
If the groups of higher priority are on the same side of the double bond, the compounds is a Z isomer.
If the groups of higher priority are diagonally placed across the double bond, the compound is a E isomer.

Question 22

Explain how priority is assigned using the Cahn-Ingot-Prelog rules

Answer 22

1. examine the atoms attached directly to the carbon atoms of the double bond and decide which of the two atoms has the highest priority. The higher the atomic number the higher the priority
2. If the two atoms attached to a carbon atom in the double bond are the same, then you will need to find the first point of difference. The group which has the higher atomic number at the first point of difference is given the higher priority