Topic 4 -Conformation Analysis and selective additions to carbonyls Flashcards

1
Q

What are conformational isomers and how do they differ?

A

Differ by their rotation around single bonds.
same compound but sat differently in 3d shape

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2
Q

what are conformational isomers also known as?

A

Conformers

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3
Q

What is the behaviour of two conformers at room temperature?

A

They rapidly interconvert via rotation around single bonds.

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4
Q

What are the two exampls of conformers that we associate with newman projections?

A

Staggered and eclipsed

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5
Q

What are the two conformers that we associate with 6 membered rings?

A

Chair and Boat

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6
Q

What is antiperiplanar?

A

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)

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7
Q

In a newman projection how can we tell which bits are antiperiplanar?

A

In a newman projection this will be up and down (directly across the circle)

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8
Q

What is the lowest energy conformation of a newman projection?

A

staggered

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9
Q

In chair conformations, generally are equatorial or axial positions prefered?

A

equatorial

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10
Q

If there is a tBu substituent on a ring, will it go in the axial or equatorial position in the chair conformation?

A

Equatorial.
tBu must be equatorial. This will overrule other interactions

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11
Q

When answering a question involving a chair conforation we must remember what?

A

that there are 2 chair conformations and they undergo ring flip. We need to draw both to establish which is the lower energy one.

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12
Q

Is the lowest energy conformation always the reactive one?

A

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.

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13
Q

what is a regioselective reaction?

A

the preference of making or breaking bonds in one direction all other possible directions.

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14
Q

what is a chemoselective reaction?

A

a reaction that operates exclusively on one functional group in the presence of other functional groups.

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15
Q

What is a stereospecific reaction?

A

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).

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16
Q

What is a stereoselective reaction?

A

a reaction in which multiple stereoisomers can be formed however one product is favoured due to its reaction pathway being more favourable than the others. Can also be a reaction where only one (or some) stereoisomer(s) among a mixture reacts.

17
Q

Shape of orbitals defines what?

A

Angles of attack of nucleophiles and stereoelectronic effects

18
Q

For E2 elimination to occur, the H and the leaving group must be what??

A

Antiperiplanar (dihedral angle of 150-180)

19
Q

For E2 elimination to occur, the H and the leaving group must be antiperiplanar, why?

A

To allow sufficient orbital overlap of the sigma (C-H) and the sigma star (C-LG) for the elimination to take place.

20
Q

In an SN2 reaction, the nucleophile attcaks from what direction and why?

A

From 180 degrees to the leaving group to overlap with the sigma star C-LG orbital.

21
Q

Nucleophillic attack of carbonyls.
Nucelophiles attack crabonyls from what angle?

A

The Burgi-Dunitz angle (107degrees)

22
Q

Nucleophillic attack of carbonyls.
Nucelophiles attack carbonyls from what angle?
Why?

A

The Burgi-Dunitz angle (107degrees)
to overlap with the pi star orbital of the C=O bond.

23
Q
A