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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
Axial
atoms/hydrogens standing perpendicular to plane of ring (up and down)
26
Equatorial
atoms/hydrogens sticking out parrallel (outwards) from thr ring
27
Chair Flip bonds...
equatorial and axial flip but wedges stay wedges and dashes stay dashes
28
Interconversions can be slowed by...
Bulky groups!!
29
Bulky Groups in Cyclohexanes
tert-butyls for example favor equatorial to reduce nonbonded strain
30
Cis
bulky groups are on same side of ring
31
Trans
bulky groups on opposite sides of rings
32
Configurational Isomer
only change form by breaking and reforming covalent bonds
33
Optical isomers
enantiomers and diasteriomers affect rotation of plane-polarized light
34
Chiral
if its mirror image cannot be superimposed on the original object; lacks internal plane of symmetry
35
Achiral
mirror image can be superimposed
36
Chiral center
4 different substituents on a carbon atom
37
Enantiomers
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
Diasteriomer
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
Optically Active Compound
if it can rotate plane-polarized light
40
Ordinary light is__
unpolarized
41
At the molecular level, one enantiomer will rotate plane-polarized light to the same magnitude but ___ direction of its mirror image
opposite
42
Dextrorotary (+)
compound that rotates polarized light to the right
43
Levorotatory (-)
compound that rotates polarized light to the left
44
Amount of light rotation depends on...and depends on...
number of molecules a light wave encounters concentration of compound and length of tube which light passes
45
Standard Conditions For Optical Measurement
1dm (10 cm) and 1 g/ml concentration
46
Specific Rotation Equation
[alpha] = [alphaobs]/(c*l) alphaobs is rotation observed , c is concentration, l is 1 dm
47
Racemic Mixture
Both + and - held in equal concentrations ro make no optical activity observed
48
Separating Enantiomers
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
For any molecule with n number chiral centers...
there are 2^n possible steroisomers
50
Diasteriomers can rotate plane-polarized light but can't tell...
the rotations of the other diasteriomer
51
Cis-Trans Isomer
type of diasteriomer substituents differ in position around an immovable bond (double/cyclic)
52
Meso Compound
contains plan of symetry causing it to lose optical properties even if it contains chiral centers equivalent of meso compounds
53
Relative/Absolute Configuration
R: configuration of one chiral molecule in relation to another A: exact spatial orientation of atoms and groups independent of other molecules
54
Cahn-Ingold-Prelog Priority Rules
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
E vs Z
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
R and S Form Procedure
1) Assign Priority 2) Invert The Stereochemistry 3) Draw a circle 4) Write the name
57
RS Assigning Priority
highest atomic number gets priority over the lowest one
58
RS: Invert the Stereochemistry
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
RS: Draw a Circle
Draw a circle going from 1->2->3 if CLOCKWISE it is R (r is right!) if COUNTERCLOCKWISE it is S
60
RS: Write the name
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
Fisher Projection: Horizontal Lines
wedges, project OUT of plane
62
Fisher Projection: Vertical Lines
dashes, project INTO the plane
63
Assigning Priority to Fisher projection
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
Assigning Priority to Fisher Projection: 0 Switches
ignore lowest priority, give numbers, make circle, write the opposite configuration
65
Assigning Priority to Fisher Projection: 1 Switches
swap lowest priority group with vertical group, make circle, write the opposite configuration
66
Assigning Priority to Fisher Projection: 2 Swtiches
swap lowest priority group to vertical, swap the remaining two, make circle, take the configuration found

Organic Chemistry (11 decks)

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