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Organic Chemistry > Isomers > Flashcards

Isomers Flashcards

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1
Q

Isomer Definition

A

compound of same molecular formula, but different molecular structures

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2
Q

Structural/Constitutional Isomers

A

only thing they share is molecular formula/weights

least similar of all isomers as they have different chemical and physical properties

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3
Q

Same Connectivity? Yes/No

A

Yes -> Stereoisomer

No -> Structural Isomer

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4
Q

Require Bond Breaking to interconvert? Yes/No

A

Yes: Configurational
No: Conformational

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5
Q

Nonsuperimpossible mirror images? Yes/No

A

Yes: Enantiomer
No: Diasteriomer

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6
Q

Physical Properties

A

characteristics that don’t change composition of matter

melting, boiling points, solubility, odor, color, density

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7
Q

Chemical Properties

A

reactivity of molecule with other molecules resulting in changes in chemical composition

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8
Q

Stereoisomers

A

share same molecular formula/weights, but also share same connectivity/molecular backbone

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9
Q

Conformational Isomer vs Configurational Isomer

A

ConFOR: differ in roation around single sigma bonds

ConFI: can be interconverted only by breaking bonds

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10
Q

Of all isomers ___ are the most similar

A

Conformational Isomers

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11
Q

Conformational Isomer

A

they are same molecule but different points in their natural rotation around a single bond

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12
Q

Staggered Conformation

A

lowest energy state, no steric repulsion

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13
Q

Anti Conformation

A

for staggered where two largest groups are antiperiplanar (same plane, opposite sides)

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14
Q

Gauche Conformation

A

staggered conformation where the two largest groups are 60 degrees apart

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15
Q

Eclipsed Conformation

A

staggered with 120 degrees

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16
Q

Totally Eclipsed Conformation

A

staggered with 0 degrees, highest energy form, least favorable as largest groups are synperiplanar (next to each other on same plane)

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17
Q

The higher the energy of the conformation the…

A

less time it will stay int he conformation

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18
Q

Conformational transitions at Room/Low Temp

A

Room: easily overturned
Low: interconversion occurs slowly due to lack of energy

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19
Q

Ring Strain

A

Cycloalkanes due to 3 reasons:

angle strain, torsional strain and steric strain

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20
Q

Angle Strain

A

bond angles deviate from what they should be

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21
Q

Torsional Strain

A

cyclic molecules take gauche or eclipsed interactions

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22
Q

Steric/van Der Waals Strain/Repulsion

A

nonadjacent atoms/groups compete for space

common in flagpole interactions for steric strain

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23
Q

Cyclohexane Conformations

A

Boat, twist and chair

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24
Q

Chair Conformation

A

most stable, lowers all 3 strains for cyclohexane

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25
Q

Axial

A

atoms/hydrogens standing perpendicular to plane of ring (up and down)

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26
Q

Equatorial

A

atoms/hydrogens sticking out parrallel (outwards) from thr ring

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27
Q

Chair Flip bonds…

A

equatorial and axial flip but wedges stay wedges and dashes stay dashes

28
Q

Interconversions can be slowed by…

A

Bulky groups!!

29
Q

Bulky Groups in Cyclohexanes

A

tert-butyls for example

favor equatorial to reduce nonbonded strain

30
Q

Cis

A

bulky groups are on same side of ring

31
Q

Trans

A

bulky groups on opposite sides of rings

32
Q

Configurational Isomer

A

only change form by breaking and reforming covalent bonds

33
Q

Optical isomers

A

enantiomers and diasteriomers

affect rotation of plane-polarized light

34
Q

Chiral

A

if its mirror image cannot be superimposed on the original object; lacks internal plane of symmetry

35
Q

Achiral

A

mirror image can be superimposed

36
Q

Chiral center

A

4 different substituents on a carbon atom

37
Q

Enantiomers

A

two molecules that are nonsumerimposible mirror images of one another

same connectivity but opposite configurations at every chiral center

HAVE SAME PHYSICAL AND CHEMICAL PROPERTIES

only difference: optical activity and reactions in chiral enviornments

38
Q

Diasteriomer

A

share same connectivity and molecules are chiral but not mirror images

DIFFERENT PHYSICAL AND CHEMICAL PROPERTIES

often because they differ at some of their chiral centers

39
Q

Optically Active Compound

A

if it can rotate plane-polarized light

40
Q

Ordinary light is__

A

unpolarized

41
Q

At the molecular level, one enantiomer will rotate plane-polarized light to the same magnitude but ___ direction of its mirror image

A

opposite

42
Q

Dextrorotary (+)

A

compound that rotates polarized light to the right

43
Q

Levorotatory (-)

A

compound that rotates polarized light to the left

44
Q

Amount of light rotation depends on…and depends on…

A

number of molecules a light wave encounters

concentration of compound and length of tube which light passes

45
Q

Standard Conditions For Optical Measurement

A

1dm (10 cm) and 1 g/ml concentration

46
Q

Specific Rotation Equation

A

[alpha] = [alphaobs]/(c*l)

alphaobs is rotation observed , c is concentration, l is 1 dm

47
Q

Racemic Mixture

A

Both + and - held in equal concentrations ro make no optical activity observed

48
Q

Separating Enantiomers

A

react with a single enantiomer to produce 2 diasteriomers which are physically different by nature and use lab techniques such as crystallization, filteration, etc. to seperate the diasteriomers and bring back original enantiomers

49
Q

For any molecule with n number chiral centers…

A

there are 2^n possible steroisomers

50
Q

Diasteriomers can rotate plane-polarized light but can’t tell…

A

the rotations of the other diasteriomer

51
Q

Cis-Trans Isomer

A

type of diasteriomer

substituents differ in position around an immovable bond (double/cyclic)

52
Q

Meso Compound

A

contains plan of symetry causing it to lose optical properties even if it contains chiral centers

equivalent of meso compounds

53
Q

Relative/Absolute Configuration

A

R: configuration of one chiral molecule in relation to another

A: exact spatial orientation of atoms and groups independent of other molecules

54
Q

Cahn-Ingold-Prelog Priority Rules

A

priority of E/Z is assigned based on the atom bonded to the double bonded carbons: the higher the atomic number, the higher the priority

**if atomic numbers are similar, compare the next atom

55
Q

E vs Z

A

E: when highest priority substituent to double bond on each side faces different direction

z: when highest priority substituent to double bond on each side faces the same direction

56
Q

R and S Form Procedure

A

1) Assign Priority
2) Invert The Stereochemistry
3) Draw a circle
4) Write the name

57
Q

RS Assigning Priority

A

highest atomic number gets priority over the lowest one

58
Q

RS: Invert the Stereochemistry

A

if lowest priority substituent isn’t in the back, switch it to the back with the other substituent and remember to switch RS for our final answer

59
Q

RS: Draw a Circle

A

Draw a circle going from 1->2->3

if CLOCKWISE it is R (r is right!)

if COUNTERCLOCKWISE it is S

60
Q

RS: Write the name

A

place R or S in parenthesis and then a hypen to the name

ex: (R)-

if multiple chiral centers, remove the hyphen and location number is within parenthesis before the R/S

ex: (3R) ….

61
Q

Fisher Projection: Horizontal Lines

A

wedges, project OUT of plane

62
Q

Fisher Projection: Vertical Lines

A

dashes, project INTO the plane

63
Q

Assigning Priority to Fisher projection

A

same rules as with RS before, just note rotating 90 degrees leads to changing of R/S

**note by rotating two pairs 90 degrees to let lowest go into the plane, you don’t have to change R/S, original stereochemistry is kept!

64
Q

Assigning Priority to Fisher Projection: 0 Switches

A

ignore lowest priority, give numbers, make circle, write the opposite configuration

65
Q

Assigning Priority to Fisher Projection: 1 Switches

A

swap lowest priority group with vertical group, make circle, write the opposite configuration

66
Q

Assigning Priority to Fisher Projection: 2 Swtiches

A

swap lowest priority group to vertical, swap the remaining two, make circle, take the configuration found

Organic Chemistry (11 decks)

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