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Organic Chem > Isomers > Flashcards

Isomers Flashcards

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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
Q

What is a carbon with four different substituents

A

A chiral center - is an asymmetrical core of optical activity

26
Q

Enantiomers

A

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
Q

Diastereomers

A

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
Q

Optical activity

A

Rotation of plane polarized light by a chiral molecule

29
Q

Polarizer

A

Allows light waves oscillating only in a particular direction to pass through producing plane polarized light

30
Q

Describe how enantiomers rotate plane polarized light

A

They will rotate it in opposite directions but with the same magnitude

31
Q

Dextrorotary

A

Compound that rotates plane polarized light to the right or clockwise d- / (+)

32
Q

Levorotary

A

Rotates plane polarized light to the left or counterclockwise l- or (-)

33
Q

How is direction of rotation determined

A

Has to be experimental - cannot determine from structure

34
Q

Specific rotation

A

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
Q

Racemic mixture

A

Contains equal conc of + and - enantiomers so it is not optically active as rotations cancel each other out

36
Q

Diastereomers

A

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
Q

How many possible stereoisomers in a molecule with n chiral centres

A

2 to the power of n possible stereoisomers

38
Q

Describe the physical and chemical properties relationship between diastereomers

A

They will have different chemical and physical properties

Will rotate plane polarized light

39
Q

Geometric isomer

A

Aka cis-trans isomer

Type of diastereomer where substituents differ in position around immobile multiple bond or ring structure

40
Q

Meso compound

A

A molecule with chiral centres that has an internal plane of symmetry so it is not optically active

41
Q

Relative configuration

A

Configuration of a chiral molecule in relation to another molecule through inter conversion

42
Q

Absolute conformation

A

The exact spatial arrangement of atoms in a chiral molecule independent of other molecules

43
Q

E and Z forms

A

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
Q

R and S forms

A

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
Q

Describe the features of a fischer projection

A

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
Q

What will happen if we:

  • rotate Fischer projection 90? 180?
  • switching a pair of substituents ? Both pairs of substituents
A

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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