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Organic Chemistry > Stereoisomerism > Flashcards

Stereoisomerism Flashcards

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1
Q

Stereoismerism

A

Compounds that are arrange differently in 3-D shape but have the same molecular formula

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2
Q

Constitutional isomers

A

Compounds that have the same molecular formula but different structure (They have different names)

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3
Q

Cis & Trans is used to differentiate stereoisomers only when comparing two _________

A

Identical groups

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4
Q

Superimposable

A

When the compound & its mirror image are identical

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5
Q

Nonsuperimposable

A

When the compound & its mirror image aren’t identical

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6
Q

Chiral

A

Nonsuperimposable compounds

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7
Q

Achiral

A

Superimposable compound

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8
Q

Chiral center

A

A carbon or atom with 4 different groups around it

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9
Q

Enatiomer

A

When a chiral compound has an nonsuperimposable mirror image (Can only have one enatiomer)

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10
Q

What are the steps for using the Cahn-Ingold-Prelog (R/S configuration)

A
  1. Assign priority to the 4 groups based on the atomic mass (largest get prioroty 1 & smallest gets 4)
  2. After assigning priority rotate the molecule so that the least priority is in the back (on a dash)
  3. Then check to see if it counts in order of 1,2,3 in clockwise rotation (R) or in the counterclockwise rotation (S)
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11
Q

When assigning priority to the 4 groups what should you do if two groups are the same mass?

A

Compare the mass of the the atoms the groups are connected to

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12
Q

When using the R/S configuration its in the __________ of the name of a compound & is italicized & in parentheses

A

Beginning, (Ex. (R)-2-butanol)

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13
Q

When multiply chiral center are present each configuration must have a _________

A

Number (ex. (2R, 3S)-3-methyl-2pentanol)

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14
Q

Enatiomers have the same ______________ because they are mirror image of each other so they have the same intermolecular forces

A

Physical Properites

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15
Q

Chiral compounds are opitcal ________ & achiral are _________

A

Active, & are not active

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16
Q

Observed rotation (⍶)

A

Dependent on the number of molecules that light encounters as it travels through the solution

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17
Q

Specific rotation ([⍶])

A

The observed rotation under standard conditions (1g/mL) (1dm)

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18
Q

When dealing with no standard condition what is the formula used for the specific rotation?

A

[⍶] = ⍶/ c x l (c is the concentration & l is the pathlength in dm)

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19
Q

Specific rotation for enantiomers are equal in ________ but _______ direction

A

Equal in magnitude but opposite in direction

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20
Q

Dextrorotory (d)

A

Compounds exhibiting a positive rotation (+) & is clockwise rotation (have nothing to do with chirality)

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21
Q

Levorotatory (l)

A

Compounds exhibiting a negative rotation (-) & is counterclockwise rotation (have nothing to do with chirality)

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22
Q

The magnitude & direction of opitcal activity can only be determined __________

A

Experimentally

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23
Q

A solution containing only a single enantiomer is ____________

A

Optically pure (enantiomerically pure)

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24
Q

Racemic mixture

A

A solution containing equal amounts of both enantiomers (1:1 ratio of enantiomers)

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25
Q

Enantiomeric excess (ee)

A

Is when there is unequal amounts of enantiomers in a solution & there is some left over

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26
Q

Formula for enantiomer excess

A

% ee = /observed ⍶/ / /⍶of pure enatiomer/ x 100%

27
Q

What are the two types of stereoisomers?

A
  1. Enantiomers- mirror image of one another
  2. Diastereomers- not mirror image of one another
28
Q

Enantiomers have the same __________ & diastereomers ________

A

Same physical properties & diastereomers dont

29
Q

What is the formula used to find the maxium amount of enatiomers

A

2n (n is the number of chiral centers)

30
Q

A molecule with an axis of symmetry has ___________ & a molecule with plane symmetry has ____________

A

Rotational symmetry, reflectional symmetry

31
Q

Chirality only depends on the presence or absence of ___________

A

Reflectional symmetry (so plane symmetry)

32
Q

A compound that has a plane of symmetry will be ________ & no plane of symmetry is ________

A

Achiral, Chiral

33
Q

Inversion

A

Reflection (symmetry) at a point & not a plane

34
Q

Meso compounds

A

Compounds that exhibit reflectional symmetry & is achrial even though it has a chirality center

35
Q

For each chirality center in a fischer projection the horizontal lines are considered to be _________ & vertical line are considered to be _________

A

Coming out of the page (wedges), going behind (dashes)

36
Q

What is the procedure for deteriming if a cyclic compound is optically active or not?

A
  1. Draw the haworth projection or just a ring with dashes & wedges for all substituents
  2. Look for a plane of symmetry
37
Q

What are the two types of stereocenters?

A
  1. Chiral center - a atom with 4 different groups around it
  2. Trigonal center - any double bonds cable of forming E or Z isomers (achiral)
38
Q

If a compound doesnt have a chiral center its ________

A

Achiral

39
Q

When theres a chiral center just put a ______ by it

A

Star

40
Q

To assign a name with the R/S configuration the least priority (4) has to be on a ________

A

Dash

41
Q

When least priority isnt on a dash then swap it with the atom so it is on a dash & when you swap the atoms you also have to swap the ___________

A

Configuration (so if it is R after the swap its actually S & vis versa)

42
Q

A compound with exactly one chiral center is always chiral & can form _________

A

Enantiomers

43
Q

A compound with two or more chiral centers are usually chiral & can form _____________

A

Diastereomers

44
Q

A compound with mulitply stereoismers will have only one ____________ & everything else is a ____________

A

Enantiomer, diastereomer

45
Q

Atropisomers

A

Molecules that contain no chiral centers but are chiral due to their inability to freely rotate (ex. allenes, substituted biphenyls, trans-cyclooctene, & BiNAP)

46
Q

How do you determine if a trigonal center is chiral or not?

A

See if it forms E or Z iosmers if so its chiral & if not its achiral

47
Q

Substituted Biphenyls

A

They are chiral if all substituents are in the ortho (next to the sigma bond) position & if none of the rings have two of the same groups on them

48
Q

Meso compounds

A

Meso compounds are created when two symmetrical centers cancel out & yielding 2 identical enantiomers

49
Q

Meso compounds have an internal ___________ which means they are usually achiral

A

Line of symmetry

50
Q

What is the formula used to determine how much stereoisomers a meso compund would have?

A

2n-1 (n is the number of chiral centers)

51
Q

What are the 3 rules to determine if a molecule is meso compound or not?

A
  1. It has to have 2 or more chiral centers
  2. It has to be atomically symmetrical (connected the same way on both sides of the compound (same atoms on both sides))
  3. An even number of chiral centers are opposites to each ohter (If one is R then other has to be S)
52
Q

What are the 3 ways to test for chirality?

A
  1. Internal line of symmetry
  2. Finding chiral centers
  3. Disubstituted cycloalknes
53
Q

What are the tpes of disubstituted cycloalkanes?

A
  1. Geminal - Disubstituted (always chiral)
  2. Middle -disubstituted (Cis= meso Compound), (Trans=chiral), (exception 1,2-cyclohexane is usually chiral some says its achiral)
  3. Para-disubstituted (always achiral, & only possible on even number rings)
54
Q

Polarimeter

A

Measures plane polarized light

55
Q

Scalemic

A

Non-perfect 1:1 ratio solution of enantiomers

56
Q

Racemic always have optical activity of ______ because it always cancels it out

A

Zero

57
Q

The enatiomeric excess (ee)

A

ee = highest % enantiomer - lowest % enantiomer

58
Q

Relatioship between observed roatation & ee

A

⍶ = [⍶] x ee

59
Q

When given the specifc rotations ([⍶]) & observed rotations (⍶) what relationships can be used to determine the ee of the mixture?

A
  1. ee = ⍶ / [⍶] (from ⍶ = [⍶] x ee)
  2. Higher % enantiomer = 100-ee/2 + ee
  3. Higher % enantiomer + lower % enantiomer = 100%
60
Q

Chirality exist on atoms that can form _______ not just only for carbon where the most common ones are Si, N, P, S

A

4 bonds

61
Q

A _________ is not chiral because its lone pair can move around due to amine inversion

A

Neutral nitrogen (only N+ are chiral (Quaternary amine))

62
Q

S+ & sulfoxides, P, Si are ______

A

Chiral

63
Q

Forumla for determining the number of steroisomer a compound will have

A

2n (n = the number of chrial centers present)

Organic Chemistry (47 decks)

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