TL - Molecular shapes and Isomerism

Question 1

Describe the bond shape for a single-bonded carbon atom

Answer 1

Their bonds are arranged like a tetrahedron with bond angle 109.5°

Question 2

Describe when the atoms round a carbon form an equilateral triangle

Answer 2

When there’s a double bond, the bond and becomes 120° and the molecule becomes trigonal planar

Question 3

Define structural isomerism

Answer 3

Molecules with the same molecular formula, but their atoms are arranged in different ways (different structural formula)

Question 4

Define stereoisomerism

Answer 4

Sterioisomers have the same molecular formula and their atoms are arranged in the same way, but the orientation of bonds in space is different

Question 5

State the 2 types of sterioisomerism

Answer 5

E/Z

Optical

Question 6

What is required for a molecule to exhibit E/Z isomerism?

Answer 6

A double bond to prevent rotation

No 2 identical groups bonded to the Carbon atom either side of the double bond

Question 7

Describe the structure of Z-isomers and give another name for Z isomerism

Answer 7

Z isomers have similar groups on the same side of the double bond
They can also be called Cis isomers

Question 8

Describe the structure of E-isomers and give another name for E isomerism

Answer 8

E isomer have similar groups going diagonally across the double bond
They can also be called Trans isomer

Question 9

For a molecule with 4 different groups surrounding a double bond, what is the arrangement of the higher priority groups for:

i) E isomers
ii) Z isomer

Answer 9

i) E isomers have their higher priority groups on opposite sides
ii) Z isomer have their higher priority groups on the same side

Question 10

Define a chiral carbon atom and give another name for chirality

Answer 10

A chiral (asymmetric) carbon atom is one that has 4 different groups attached to it

Question 11

Explain why chirailty causes optical isomers and give another name for optical isomers

Answer 11

It is possible to arrange the groups in 2 different ways around the carbon atoms so that 2 different molecules are made - these molecules are optical isomers (AKA enantiomers)

Question 12

Define an enantiomers

Answer 12

Enantiomers are mirror images and no matter which way you turn them, they cannot be superimposed

Question 13

What letters are given to different enantiomers?

Answer 13

D and L

Question 14

Give an example of a naturally ouring L enantiomer

Answer 14

L-amino acids

Question 15

Describe how you draw optical isomers

Answer 15

1) Find the chiral centre
2) Draw one enantiomer in a tetrahedral shape (don’t draw the full structure of each group).
3) Draw the mirror image beside the first enantiomer