Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Chemistry > CHEM 1009- Stereochemistry > Flashcards

CHEM 1009- Stereochemistry Flashcards

You may prefer our related Brainscape-certified flashcards:
Chemistry 101 flashcards Periodic Table flashcards AP® Chemistry flashcards Organic Chemistry 101 flashcards
1
Q

What is constitutional isomers

A

For a given formula, different ways to arrange the molecule.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What is stereoisomerism

A

Have the same connectivity but differ in 3D orientation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What two groups are stereoisomers divided into

A

enantiomers
diastereoisomers

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What does a molecule being chiral mean

A

structures are chiral when they cannot be superimposed onto their mirror image

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

How do you tell whether a molecule is chiral or achiral

A

if the molecule has a plane of symmetry then it is achiral, if it doesn’t then it is chiral.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Any planar molecule is chiral. Why?

A

As there is always a plane of symmetry which goes through the plane of the paper.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is a stereogenic centre

A

a stereogenic centre is a carbon atom which have 4 different groups attached to it.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

True or false. Molecules with a stereogenic centre are always chiral.

A

True. A stereogenic centre means that there cannot be a plane of symmetry

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Does a reaction with two chiral molecules always result in a racemic mixture

A

yes

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What does enantiomerically pure mean

A

That the molecule produced is only one enantiomer of a chiral compound

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What two letters are used for the nomenclature for enantiomers

A

R and S

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

How do we determine if an enantiomer is R or S

A

Using CIP rules, we label each of the atoms attached to the carbon 1 to 4, 1 being the largest atomic number going to 4 being the smallest. Then rotate the molecule such that the lowest priority group is facing away i.e into the page or at the back of the molecule. We then draw a circle from 1 to 4. If the circular arrow is going clockwise then this will R. If the arrow is going anticlockwise then this will be S.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What to do if when using CIP the atom directly attached to the centre carbon is the same.

A

You go to the next atom along that is bonded to it and the highest atomic number is assigned the higher priority

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What does it mean for a compound to be optically active.

A

It means that the compounds will rotate the plane of polarised light

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

In what way do enantiomers rotate the polarised light.

A

By an angle alpha. One enantiomer will rotate it by alpha degrees and the other enantiomer will rotate it by minus alpha degrees

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What does alpha depend on

A

Conc., path length, temperature and the wavelength of light

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What are the perimeters for the specific rotation

A

Experiment done at 20 degrees c and using the same wavelength of light known as the d line

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

For nomenclature, what two things do we have to add to to distinguish between enantiomers

A

If it is R or S and if it rotates the plane of polarised light by positive alpha or negative alpha, symbolised by a + or -

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

what to do when a molecule has two stereogenic centres.

A

Draw out each isomer and determine whether the stereogenic centres are S or R. Note that the answer is the opposite when the molecule is the same just with the opposite atoms pointing towards and out of the page.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

How many possibilities of isomers are there for a molecule with two stereogenic centres.

A

4… R,S S,R S,S R,R

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

How are the R,R and S,S related to each other

A

These are enantiomers are they are non superimposable mirror images of each other

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

How are the R,S and S,R related to each other

A

These are enantiomers are they are non superimposable mirror images of each other

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

What happens if you only swap one stereogenic centre i.e R,S and S,S

A

These are not enantiomers as the are not mirror images. This holds true for only swapping one stereogenic centre.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

What are diastereoisomers

A

Stereosimers whihc are not mirror images and are non-superimposable on eachother. When you have a molecule with two stereogenic centres which are isomers of each other but not enantiomers i.e R,S and S,S

25
Q

If you have n number of stereogenic centres, then how many possible isomers do you have. These isomers being enantiomers and distereoisomers

A

2 to the power n

26
Q

What happens if the two stereogenic isomers are identical.

A

Then only S,S and R,R are enantiomers. There is one more distereosimer of S,R which isn’t chiral and therefore can’t have an enantiomer. so R,S is identical to S,R

27
Q

What is the name given to the process of separating enantiomers

A

Resolution

28
Q

How is resolution carried out

A

We mix our racemic mixture of R,S with an enantiomerically pure reagent R. This will create two molecules that are distereoisomers of each other… R,R and S,R. Then we have to separate these to separate beakers. Disteriosomers Bp have different properties therefore It could be possible to remove the reagent just leaving R and S separately

29
Q

What are absolute sterochemsitry

A

this is when we can give a definitive R or S value to the enantiomers

30
Q

What are relative stereochemistry

A

This is when you have got two or more stereogenic centres and is the sterochemical relationship between one atom or group in the molecule to another atom or group in the molecule

31
Q

What prefixes do we use for ringed molecules

A

Cis and trans

32
Q

When do we use the cis and trans prefix for ringed molecules

A

When the two main substitutes on the ring are both pointing either upwards or downwards this is known as the cis isomer. the opposite is true for trans

33
Q

cis and trans isomers are examples of relative stereochemistry. Why?

A

This is because you are not saying if the stereogenic centres are R or S but rather if they are pointing in the same direction.

34
Q

Same is true for chain isomers but what prefix do we use then

A

syn and anti

35
Q

What group of isomers do double bond isomers(E and Z) belong too

A

Distereoisomers as they are both non superimposable and not mirror images

36
Q

What is a conformational isomer

A

Two molecules that are only different by a rotation of a c-c single bond

37
Q

How are molecules arranged in eclipsed form

A

When the hydrogens on an ethane molecule are lined up.

38
Q

How are molecules arranged in the staggered formation

A

When the hydrogens on ethane are rotated such that they are as far away as possible to the hydrogens on the other side.

39
Q

What does a Newman projection show.

A

The end on view of a molecule, showing that it is either eclipsed or staggered.

40
Q

How do we draw a Newman projection for an eclipsed molecule

A

We draw a circle to represent the carbon at the back with three lines coming off representing hydrogen. Then to represent the hydrogens at the front the 3 lines from the hydrogens extend into the centre of the circle. as this is the eclipsed form the hydrogens are drawn such that they are as far away as possible.

41
Q

How do we draw a Newman projection for an staggered molecule

A

We draw a circle to represent the carbon at the back with three lines coming off representing hydrogen. Then to represent the hydrogens at the front the 3 lines from the hydrogens extend into the centre of the circle. as this is the staggered form the hydrogens are drawn such that they are as close to each other as possible to represent them being on top of each other.

42
Q

Which conformation is always the lowest energy

A

Staggered is always the lowest energy as there is less repulsion from the atomic orbitals as in eclipsed they are as close as they can be. When eclipsed the electrons repel in the atomic orbital but in staggered the sigma bonding orbital is next to the sigma star antibonding orbital which make sit more favoured

43
Q

What conformation is best when there are two bulky groups either side.

A

Still is more favoured to be staggered but the bulky groups want to be as far away as possible. Therefor it is favoured for staggered and the two bulky groups on oppsoite ends.

44
Q

Antiperiplanor meaning and is It more favoured

A

yes it is as it means the opposite to inside the plain of the paper

45
Q

syn periplaner more favoured?

A

no it is the least favoured

46
Q

Is cyclohexane planar

A

NO!

47
Q

What are the two conformations called of cyclohexane

A

The chair and boat conformation

48
Q

Which conformation of cyclohexane is the lowest in energy

A

The chair

49
Q

Which conformation of cyclohexane is the highest in energy

A

The boat

50
Q

What does the chair conformation look like

A

It has 4 of the carbons planar and one pointing upwards and one pointing downwards

51
Q

What does the chair conformation look like

A

It has 4 of the carbons planar and the other two carbons pointing upwards/downwards

52
Q

In cyclohexane the hydrogens occupy one of two positions. what are these positions

A

Axial and equatorial

53
Q

Can cyclohexane undergo ring flipping

A

yes

54
Q

What is ring flipping, and how does it impact the conformation of cyclohexane

A

Ring flipping is a process where cyclohexane undergoes a conformational change, interconverting between its chair conformations.This process involves the upward movement of of substituents on axial positions to equatorial positions and visa versa.

55
Q

Are two molecules which are ring flips conformational isomers

A

Yes as only the rotation of a single carbon bond is needed.

56
Q

When a substituent is bonded onto cyclohexane, is it better for it to be axial or equatorial.

A

Equatorial. This is because when it’s axial there is more repulsion from the other two hydrogens which are pointing the same way.

57
Q

What position do larger substituted groups use on a cyclohexane molecule.

A

Always lower energy for larger groups to be equatorial.

58
Q

If there are two substitutes on cyclohexane and they are both pointing up, how will they be arranged.

A

The bulkiest group will be equatorial and the smaller group will be axial. and they’ll both point down/up.

59
Q

If there are two substitutes on cyclohexane and one is pointing up with the other pointing down, how will they be arranged.

A

The bulkiest group will be equatorial up whilst the other one will be equatorial down.

Chemistry (3 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions