Topic 4 -Conformation Analysis and selective additions to carbonyls Flashcards
What are conformational isomers and how do they differ?
Differ by their rotation around single bonds.
same compound but sat differently in 3d shape
what are conformational isomers also known as?
Conformers
What is the behaviour of two conformers at room temperature?
They rapidly interconvert via rotation around single bonds.
What are the two exampls of conformers that we associate with newman projections?
Staggered and eclipsed
What are the two conformers that we associate with 6 membered rings?
Chair and Boat
What is antiperiplanar?
Where the dihedral angle between two molecules is between 150-180 degrees.
In a newman projection this will be up and down (directly across the circle)
In a newman projection how can we tell which bits are antiperiplanar?
In a newman projection this will be up and down (directly across the circle)
What is the lowest energy conformation of a newman projection?
staggered
In chair conformations, generally are equatorial or axial positions prefered?
equatorial
If there is a tBu substituent on a ring, will it go in the axial or equatorial position in the chair conformation?
Equatorial.
tBu must be equatorial. This will overrule other interactions
When answering a question involving a chair conforation we must remember what?
that there are 2 chair conformations and they undergo ring flip. We need to draw both to establish which is the lower energy one.
Is the lowest energy conformation always the reactive one?
No, it is possible for some of the lowest energy conformations to not have the right requirements for certain reactions. Therefore it may have to undergo a change such as a ring flip to a higher energy conformation to meet these requirements and thus react.
what is a regioselective reaction?
the preference of making or breaking bonds in one direction all other possible directions.
what is a chemoselective reaction?
a reaction that operates exclusively on one functional group in the presence of other functional groups.
What is a stereospecific reaction?
the stereochemistry of the product is dependent on the stereochemistry of the starting material (stereochemistry of the reactant completely determines the stereochemistry of the product).