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Isomers Flashcards

1
Q

Isomer

A

Have same molecular formula but different structure

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2
Q

Structural isomer

A

Aka constitutional isomer - all they share is molecular formula/weight
Least similar of all isomers

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3
Q

Physical properties

A

Processes that don’t change the composition of matter

Eg. melting point, boiling point, solubility, odour, colour, density

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4
Q

Chemical properties

A

Reactivity of molecule with other molecules and as a result changes in chemical composition -functional groups

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5
Q

Stereoisomer

A

Same chemical formula as well as same atomic connectivity but differ in spatial arrangements - can be conformational or configurational

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6
Q

Conformational isomer

A

Aka conformer - most similar - are the same molecule just at different points in their natural rotation around alpha bond
-single bonds free to rotate

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7
Q

Staggered (anti) conformation

A

Two largest groups are antiperiplanar - minimal steric repulsion - 180 apart - most energetically favourable

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8
Q

Gauche

A

Type of staggered conformation where two largest molecules are 60 apart

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9
Q

Eclipsed

A

Two largest groups are 120 apart - must pass through eclipsed when going from anti to gauche

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10
Q

Totally eclipsed

A

Two largest groups directly overlap with 0 degrees between them - highest energy state and least favourable - synperiplanar

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11
Q

Ring strain

A

Seen in cyclic groups - arises from angle strain, torsional strain and non-bonded/steric strain

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12
Q

Angle strain

A

Results when bond angles deviate from their ideal values by being stretched or compressed

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13
Q

Torsional strain

A

Results when cyclic molecules must assume confirmations that are eclipsed or gauche

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14
Q

Non-bonded strain

A

Van der waals repulsion - when non adjacent atoms or groups compete for the same space - dominant source of steric strain in flagpole interactions of cyclohexane boat

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15
Q

Three conformations of cyclohexane

A

Chair, boat, twist(skew boat)

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16
Q

Most stable form of cyclohexane

A

Chair conformation - eliminates all 3 types of strain

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17
Q

Axial

A

Up and down - bonds perpendicular to plane of ring

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18
Q

Equatorial

A

Parallel / sticking out horizontal

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19
Q

Chair flip

A

One chair form is converted to another - axial becomes equatorial and equatorial becomes axial - conversion slowed by bulky groups such as tert-butyl

20
Q

Where do bulky groups sit in chair conformation

A

Will favour equatorial to avoid non-bonded strain/flagpole interactions with axial groups

21
Q

Configurational isomers

A

Can only change from one to another by breaking and reforming covalent bonds
Consists of enantiomers and diastereomers

22
Q

Optical isomer

A

Have different special arrangements that affects the rotation of plane polarized light
Included enantiomers and diastereomers

23
Q

Chiral

A

Mirror image cannot be superimposed over original object - lacks an internal plane of symmetry
Eg. hands

24
Q

Achiral

A

Object has mirror image that can be superimposed

Has a plane of symmetry

25
What is a carbon with four different substituents
A chiral center - is an asymmetrical core of optical activity
26
Enantiomers
A type of configurational isomer that has non-superimposable mirror images Have the same connectivity but opposite configurations at every chiral centre Have identical physical and chemical properties except for optical activity and reactions in chiral environments
27
Diastereomers
A type of configurational isomer that are chiral and share the same connectivity but are not mirror images because they differ in some of their multiple chiral centres
28
Optical activity
Rotation of plane polarized light by a chiral molecule
29
Polarizer
Allows light waves oscillating only in a particular direction to pass through producing plane polarized light
30
Describe how enantiomers rotate plane polarized light
They will rotate it in opposite directions but with the same magnitude
31
Dextrorotary
Compound that rotates plane polarized light to the right or clockwise d- / (+)
32
Levorotary
Rotates plane polarized light to the left or counterclockwise l- or (-)
33
How is direction of rotation determined
Has to be experimental - cannot determine from structure
34
Specific rotation
Rotation determine for specific conc of an optically active molecule and tube length compared to standard [alpha]=alpha(obs)/(cxl) [alpha] is specific rotation in degrees C is concentration in g/ml L is path length in dm Standard conc is 1g/ml and length is 1dm(10cm)
35
Racemic mixture
Contains equal conc of + and - enantiomers so it is not optically active as rotations cancel each other out
36
Diastereomers
Non mirror image configurational isomer Has 2 or more stereogenic centres and differs at some but not all of these Must have multiple chiral centres
37
How many possible stereoisomers in a molecule with n chiral centres
2 to the power of n possible stereoisomers
38
Describe the physical and chemical properties relationship between diastereomers
They will have different chemical and physical properties | Will rotate plane polarized light
39
Geometric isomer
Aka cis-trans isomer | Type of diastereomer where substituents differ in position around immobile multiple bond or ring structure
40
Meso compound
A molecule with chiral centres that has an internal plane of symmetry so it is not optically active
41
Relative configuration
Configuration of a chiral molecule in relation to another molecule through inter conversion
42
Absolute conformation
The exact spatial arrangement of atoms in a chiral molecule independent of other molecules
43
E and Z forms
Looking at polysubstituteed double bonds - find highest priority substituents attached to carbon based on molecular weight - if both on the same side of double bond it is z - if on opposite sides it is E
44
R and S forms
Used for chiral/sterogenic centres. Assign priority based on atomic weight. Switch lowest priority group with the group pointing into page. Draw a circle from 1 to 3 - ignoring 4. If it is clockwise it is R and counterclockwise is S BUT THEN HAVE TO PICK OPPOSITE BECAUSE LOWEST PRIORITY GROUP WAS MOVED
45
Describe the features of a fischer projection
Horizontal lines project out of plane (wedges) Vertical lines project into page (dashes) Lowest priority must go into pages so can be top or bottom
46
What will happen if we: - rotate Fischer projection 90? 180? - switching a pair of substituents ? Both pairs of substituents
Rotating 90 or switching one pair of substituents will cause inversion Rotating 180 or switching both pairs will retain stereochemistry

Organic Chem (6 decks)

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