Isomerism

What is a constitutional/structural isomer?

It is where you have to break the bonds to form a different molecule. They have different core names

What is a conformational isomer?

It is rotating about bonds of the same molecule.

What are stereoisomers?

They have the same order of attachment but different spatial positioning of the attachment

What are the 2 types of stereoisomers?

1. Geometrical isomers

2. Stereogenic/chiral centers

What do you call a dihedral angle between two groups of 180 degrees?

Anti

What do you call a dihedral angle between two groups of 60 degrees?

Gauche

What do you call a dihedral angle between two groups of 0 degrees?

Eclipsed

Is staggered or eclipsed more stable?

Staggered conformation is more stable

Why is staggered conformation more stable?

This is because the groups are not occupying the same space.

What conformation is the most stable?

Anti

Why is eclipsed conformation the least stable?

This is because the two substituents are trying to occupy the same space.

What is a diastereomer?

It is when at least one of the stereochemical features has changed. Not all

What does number of stereoisomers depend on? What is the formula for determining the number of stereoisomers?

Number of stereocentres. 2^n where n is the number if stereocenters.

What are axial substituents?

They are on chair conformations where 3 will go up to the sky and 3 will go to the floor.

What are equatorial substituents?

They are on chair conformations and are parallel to the line it isn’t joined to.

Is a sky substituent usually on a wedge or hash?

Its on a wedge

Is a floor substituent usually on a wedge or a hash?

Its on a hash

Is there one sub that goes to the sky and one that goes to the floor on every C on the chair?

Yes there is

What does size of the destabilization energy depend on?

Effective size of the substituents

When does the biggest substituents (effective size) see most destabilization?

When in eclipsed conformation

When does the biggest substituents (effective size) see the least destabilization?

When in anti conformation (staggered)

What is the effective size of H substituent?

0

What is the effective size of sp substituents (nitrile, alkynes)?

1

What is the effective size of halogen substituent?

2

What is the effective size of sp2 (carboxylic acid, ester, ether) substituent?

3

What is the effective size of sp3 (methyl sub) substituent?

7

What is the effective size of sp3 (ethyl sub) substituent?

7.5

What is the effective size of sp3 (iso-propyl) substituent?

13

What is the effective size of sp3 (tert-butyl) substituent?

20

What are enantiomers?

They are non-superimposable mirror images

What is a chiral, stereocenter, sterogenic molecule?

It is where the carbon has 4 different substituents

What happens to the substituents on a chair conformation when you do a ring flip?

The substituents will switch from axial to equatorial and from equatorial to axial. However, if they are towards the sky then they will still be towards the sky and same applies to the floor.

Is axial or equatorial substitution more stable?

Equatorial substitution

Should the larger substutuient be placed on the axial or equatorial substituent?

On the equatorial substituent