Isomers

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1

What are isomers?

Isomers are two or more molecules with the same molecular formulas but different arrangements of atoms

2

What are two categories of isomers?

Constitutional isomers

Stereoisomers

3

What are constitutional isomers?

Isomers with the same molecular formula but different structural formula because they have different connectivity from one another.

4

What are stereoisomers?

Isomers with the same molecular formula and structural formula because they share the same connectivity but differ in their configuration in three dimensional space.

5

What are two categories of stereoisomers?

Confirmational

Configurational

6

What are confirmational isomers

Isomers that can be interconverted just by rotations about formally single bonds.

7

What are configurational isomers?

Isomers that can cannot be converted into one another by rotation around a single bond.

8

What are the two categories of configurational isomers?

Geometric

Optical

9

What are geometric isomers?

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Isomers that are locked into their spatial positions with respect to one another due to a double bond or a ring structure.

10

What are optical isomers?

Isomers that differ three-dimensionally by the placement of substituents around one or more atoms in a molecule.

11

E/Z isomers are what type of isomer?

Geometric

12

R/S isomers are what type of isomer?

Optical

13

What is chirality?

4 different atoms around a central atom can appear in two different configurations that are mirror images of each other.

14

What is the first step to tell if a molecule is R or S?

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1. Assign priority to each substituent around the the chiral center by increasing atomic numbers

15

What is the second step to tell if a molecule is R or S?

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Build the 3D model

White = Hydrogen

Black = Carbon

Red = Oxygen

Grey = Chlorine

Green = Iodine

16

What is the third step to tell if a molecule is R or S?

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Position the model so the lowest priority substituent goes to the back away from you.

CH3 is positioned to the back

17

What is the fourth step to tell if a molecule is R or S?

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Draw the 3 substituents in the front of the compound as a Newman projection .

18

What is the fifth step to tell if a molecule is R or S?

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Draw an arrow around the Newman projection going from highest to lowest priority of the remaining substituents

19

After drawing the arrow around the Newman projection how do you know if the molecule is R or S?

R: If the arrow runs clockwise

S: If the arrow runs counter clockwise

20

What is a cis isomer?

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Molecule where both substituents in a ring are on the same plane. Both are wedges or both are dashes.

21

What is a trans isomer?

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Molecule where substituents in a ring are on opposite planes. One is a dash and one is a wedge.

22

Constitutional isomers that are more branched have a __________ boiling point. This is because of __________ inter-molecular forces.

Lower

Weak

(porcupine)

23

Constitutional isomers that are less branched have a __________ boiling point. This is because of __________ inter-molecular forces.

Higher

Strong

(snake)

24

Which is more stable?

cis or trans?

Trans

25

When is E/Z used?

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When there is 1 or 0 hydrogens directly attached to the double bond.

26

When is cis/trans used?

When there are 2 Hydrogens directly attached to the double bond