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Flashcards in Ch 2 - Isomers Deck (25):
1

Structural or constitutional isomers

The most different. They only share molecular (ex C6H14) formula

2

Physical properties

Color, odor, density, boiling point, melting point , solubility
Characteristics of processes that don’t change the composition of matter

3

Chemical properties

Reactivity of molecule with other molecules results in change in composition

4

Stereoisomers

Same chemical formula
Same atomic connectivity (same structural backbone)
All isomers that are not constitutional fall in this category
Broken down into conformational and configurational

5

Conformational isomers

Also called conformers
The most similar isomers
Same molecule at different points in their natural rotation around a sigma bond.

6

Staggered conformation

Newman projection - along the line of site - there is no overlap except for the unavoidable Cs that are directly in front and behind each other

7

Anti conformation

Type of staggered conformation that is most energetically favored
Two largest groups are antiperiplanar (in the same plane but on opposite sides)

8

Gauche

Type of staggered conformation where the two largest groups are 60 degrees from each other

9

Eclipsed conformation

Eclipsed is two methyl groups are 120 degrees apart and overlap with the hydrogen atoms
When the methyl groups directly overlap it is totally eclipsed. Least favorable energetically because two largest groups are synperiplanar (same plane, same side)

10

Ring strain

Arises from three factors:
Angle strain - bond angles deviate form ideal by being stretched or compressed
Torsional strain - cyclic molecules must assume eclipsed or gauche conformations
Non bonded strain (van der waals repulsion) - nonadjacent atoms or groups compete for same space

11

Equatorial

Over
Parallel

12

Axial

Up and down

13

Configurational isomers

Can only change from one form to another by breaking and reforming covalent bonds.
Two types - enantiomers and diastereomers, both also called optical isomers

14

Chirality

Object is chiral if its mirror image cannot be superimposed
Lacks internal plane of symmetry

15

Enantiomers

Nonsuperimposable mirror images of each other.
Same connectivity but opposite configurations at every chiral center
Identical physical and chemical properties except for optical activity and reactions in chiral environments

16

Optical activity

Rotation of plane polarized light by a chiral molecule. Direction Only determined through experiment
Rotation to right or clockwise is dextrorotatory (d) and is labeled +
Rotation to left or counter is levorotatory (l) or -

17

Specific rotation

[alpha]=alpha sub obs/(c times l)
[alpha] is specific rotation in degrees
Alpha sub obs is observed rotation in degrees
C is the concentration in g/ml
l is the path length in dc (10 cm)

18

Racemic mixture

When both + and - enantiomers exist in equal concentrations together

19

Diastereomers

Non-mirror image configurational isomers
Differ at some but not all of their necessarily multiple chiral (stereogenic) centers

20

Cis-trans isomers

Also geometric isomers
Substituents differ in their position around an immovable bond
Same side of bond = cis
Different = trans

21

Meso compounds

Compounds with chiral centers within but also containing an internal plane of symmetry and therefore having no optical activity

22

Relative configuration

Chiral molecule’s configuration in relation to another chiral molecule (often through chemical inter conversion)

23

Absolute confirmation

Describes exact spatial arrangement of atoms or groups independent of other molecules

24

E and Z forms

Polysubstituted compounds
Identify highest priority substituent attached to each double bonded carbon by atomic number or neighboring atomic number
If substituents are on same side it’s Z if not, E

25

Chan-Ingold-Prelog priority rules

Priority is based on highest atomic number. If tied then priority is given to next atom outward until they do not tie anymore.