OChem2 Isomers

Question 1

Chemical compounds that have the same molecular formula but differ in their atomic connectivity, rotational orientation, or 3D position of their atoms

Answer 1

Isomers

Question 2

Compounds that share ONLY their molecular formula, their atomic connections may be completely different. They often have very different chemical and physical properties.

Answer 2

Structural Isomers

Question 3

Isomers with the same chemical formula with the same atomic connectivity. The only difference is how atoms are arranged in space.

Answer 3

Stereoisomers

Question 4

Compounds that differ in the position of substituents attached to a double bond.

If two substituents are on the same side, the double bond is calleda __ double bond

If they are on opposite sides, it is called a ___ double bond

Answer 4

Geometric isomers

Cis

Trans

Question 5

If the two highest priority substituents of a polysubstituted double bond are lie on the same side of the double bond, it is called

If the two highest substituents lie on opposite sides, it is called

Answer 5

Z

E

Question 6

An object that is not superimposable upon its mirror image is called

Objects that can be superimposed are called

Answer 6

Chiral

Achiral

Question 7

How many different substituents must a carbon have to be considered chiral?

Answer 7

4

Question 8

Chiral objects that are nonsuperimposable mirror images are a specific type of stereoisomer and are called

Answer 8

enantiomers

Question 9

The configuration of a chiral molecule relative to another chiral molecule

This describes the spatial arrangement of these atoms or groups

Answer 9

Relative configuration

Absolute configuration

Question 10

If the priority of a chiral molecule is counterclockwise, it is

If it is clockwise, it is

Answer 10

S

R (clockwise is like turning steering wheel to the right)

Question 11

Which take higher priority: molecules of higher atomic number or lesser atomic number

Answer 11

Higher atomic numbers take precedence

Question 12

Enantiomers have identical chemical and physical properties except for one exception, what is it?

Answer 12

Optical activity

Question 13

A compound that rotates the plane of polarized light to the right, or clockwise, is_____ and is labeled ____

A compound that rotates the plane of polarized light to the left, or counter clockwise, is ___ and is labeled ____

Answer 13

Dextrorotatory (+)

Levorotatory (-)

Question 14

The amount of rotation of light due to chirality depends upon two things…

What is the specific rotation equation?

Answer 14

Concentration of the chiral molecule
Length of tube through which is passes

specific rotation = observed rotation/(concentration *length)

Question 15

A mixture of equal concentrations of both the + and - enantiomers of a chiral molecule is called

Is optical activity observed?

Answer 15

Racemic mixture/modification

No.

Question 16

For any molecule with n chiral centers, how many possible steriosomers are there?

For example, 2 chiral centers = how many possible steriosomers

Answer 16

2^n

4

Question 17

Sterioisomers that are not mirror images are called

Answer 17

Diasteriomers

Question 18

A molecule with 2 or more chiral centers that has a line of symmetry within it is called a

Are they optically active?

Answer 18

meso compound

Nope.

Question 19

Compounds that differ only by rotation about one or more single bonds. Essentially they represent the same compound in a slightly different position

What is use to depict the different configurations?

Answer 19

Conformational isomers

Newman projection

Question 20

The most stable conformation is when 2 methyl groups on a molecule with two chiral centers are oriented ____ degrees from each other

There is no overlap in the line of sight so the molecule is said to be in ___ conformation

Answer 20

180 degrees

staggered, anti

Question 21

The other type of staggered conformation, called ____, occurs when the two methyl groups of a molecule with two chiral centers are 60 degrees apart

Answer 21

Gauche

Question 22

To convert from the anti to the gauche conformation, the molecule must pass through an _____ conformation in which the two methyl groups are 120 gegrees apart and overlap with the H atoms on the adjacent carbon.

When two methyl groups overlap with each other, the molecule is said to be _____ and is in its highest energy state

Answer 22

Eclipsed

Totally eclipsed (think solar eclipse)

Question 23

In cycloalkanes, this type ostrain results when bond angles deviate from their ideal values

This type occurs when cyclic molecules must assume conformations that have eclipsed interactions

This results when atoms or groups compete for the same space

Answer 23

Angle Strain

Torsional Strain

Nonbonded Strain

Question 24

What is the most stable conformation of cyclohexane?

Why?

Answer 24

The chair conformation

All 3 types of strain are eliminated

Question 25

In the chair conformation of cyclohexane, the hydrogen atoms that are perpendicular to the plane of the ring are called

The ones that are parallel are called

Which position is favored?

Answer 25

Axial

Equatorial

The equatorial position because of steric repulsion with other axial substituents

Question 26

The interconversion between the two chairs can be slowed or even prevented if a sterically _____ group is attached to the ring

Answer 26

Sterically bulky, i.e.t-butyl

Question 27

Bulky substituents prefer the axial or the equatorial position?

Answer 27

Equatorial

Question 28

How does a Br2 molecule add to double bonds?

Answer 28

Anti. Not syn.