Chapter 2 - Isomers

Question 1

Structural (constitutional isomer )

Answer 1

Molecular formula and molecular weights are all the same

Question 2

Physical properties

Answer 2

Processes that don’t change the composition of matter

Question 3

Examples of physical properties

Answer 3

Melting point
Boiling point 
Solubility 
Odor 
Colour 
Density

Question 4

Chemical properties

Answer 4

Change the composition of matter by reacting with other molecules
Functional groups of molecule *

Question 5

Acetone structure

Answer 5

CH3-C(O)-CH3

Question 6

Stereoisomers

Answer 6

Share same atomic connectivity

Question 7

Conformational isomers

Answer 7

Rotate around a single bond

- same molecule but are in a different point of rotation

Question 8

Configurational isomer

Answer 8

Only interconverted by breaking a bond

Question 9

Newman projection

Answer 9

Visualized along a line extending through carbon carbon axis

Question 10

Staggered ( anti ) conformation

Answer 10

When two largest groups are 180 degrees apart

Most stable conformation

Question 11

Staggered (gauche) conformation

Answer 11

Two largest groups are 60 degrees apart

Question 12

Staggered ( eclipsed ) conformation

Answer 12

The two largest groups are 120 degrees apart

Question 13

Totally eclipsed

Answer 13

Highest energy state

When the two largest groups are semiplanar

Question 14

What are three types of ring strain ?

Answer 14

Angle strain
Torsional strain
Nonbonded strain

Question 15

Angle strain

Answer 15

Bonded angles deviate from their ideal values by being stretched or compressed

Question 16

Torsional strain

Answer 16

When cyclic molecules assume eclipsed or gauche interactions

Question 17

Nonbonded strain ( van der waals repulsion )

Answer 17

Nonadjacent carbons compete for the same space

Question 18

Axial

Answer 18

Hydrogen atoms that stick up or down

Question 19

Equatorial

Answer 19

Hydrogens that stick out

Question 20

Chair flip

Answer 20

All axial become equatorial and vice versa

Question 21

What conformation do bulkier groups favour ?

Answer 21

Equatorial

Question 22

What happens in rings with more than one substituent ? Which conformation is favoured ?

Answer 22

The preferred chair position is the one in which the larger group is in the equatorial position

Question 23

Cis

Answer 23

If both groups are located on the same side of the ring

Question 24

Trans

Answer 24

If both groups are located on the opposite side of the ring

Question 25

Chiral

Answer 25

Mirror image that can not be super imposed

Question 26

Chiral center

Answer 26

Carbon is bonded to 4 different substituents

Question 27

Enantiomer

Answer 27

Nonsuper imposable mirror image | Nearly identical physical and chemical properties except optically activity and reactions in chiral environment

Question 28

Diastereomers

Answer 28

Chiral and have the same connectivity Not mirror images Each have different chemical properties but may behave similarly due to the same functional group Also rotate plane polarized light which is not equal in magnitude to mirror image Differs by at least one but not all chiral carbons

Question 29

Optically active

Answer 29

Rotation of the plane polarized light by a chiral molecule | Light is rotated in the same magnitude but opposite direction of the mirror image

Question 30

Dextrorotatory (d-) +

Answer 30

Polarizes light to the right out clockwise

Question 31

Levorotatory (l) -

Answer 31

Compound that rotates light counterclockwise or to the left

Question 32

What does the amount of rotation of the plane polarized light depend on ?

Answer 32

Concentration of optically active compound | Length of tube

Question 33

Specific rotation equation

Answer 33

[alpha]=alpha obs/ c x l [alpha]-specific rotation in degrees Alpha obs- observed rotation in degrees C - concentration in g/mol L - path length in dm

Question 34

Racemic mixture

Answer 34

Equal concentrations of (+) and (-) are present so the rotations cancel out and no optical activity is observed

Question 35

Geometric isomer

Answer 35

Substituents differ in their position around and immovable bond

Question 36

What is the criteria for a compound to be optically active ? What is a mess compound ?

Answer 36

1. Chiral center 2. No internal plane of symmetry Meso compound - chiral carbon + plain of symmetry

Question 37

Relative configuration

Answer 37

Spatial arrangement of chiral molecules with respect to other molecules

Question 38

Absolute configuration

Answer 38

Spatial configuration of chiral molecules independent of other molecules

Question 39

Z forms

Answer 39

Two highest priority group on double bond are on the same side

Question 40

E forms

Answer 40

Two highest priority groups on double bond are on opposite sides

Question 41

What compounds require the use of E and Z forms ?

Answer 41

Polysubstituted double bonds