Isomers

Question 1

What are Structural Isomers?

Answer 1

-They are the least similar of all isomers, all they have in common are their molecular formula and thus their molecular weights are the same

Question 2

What are Physical Properties?

Answer 2

No change in composition of matter, including MP, BP, solubility, odor, color, and density

Question 3

What are Chemical Properties?

Answer 3

The reactivity of the molecule, resuts in a change in composition, functional groups determine reactivity

Question 4

What are STEREOISOMERS?

Answer 4

Isomers that have the same structural backbone, but differ in how their atoms are arranged in space (wedges and dashes)
All isomers that are not structural isomers are stereoisomers

Question 5

What are the two classes of Stereoisomers?

Answer 5

Conformational isomers differ in rotation around a single bond, and Configurational isomers can be interconverted only by breaking bonds

Question 6

What are the four kinds of conformations that a Newman Projection can depict a molecule in?

Answer 6

Staggered, Gauche, Eclipsed, Totally Eclipsed

Question 7

What configuration has the lowest energy, which has the highest?

Answer 7

Staggered, then totally eclipsed

Question 8

**What are the three conformations the MCAT will present cyclohexane in?

Answer 8

Chair, Boat, and Skew-Boat

Question 9

How can the interconversion of cyclohexane in a CHAIR FLIP be stopped?

Answer 9

By attaching a bulky group to the ring, tert-butyl groups are a classic example on the MCAT

Question 10

In what position do you want you largest groups, Equatorial or Axial?

Answer 10

Equatorial, reduces nonbonded strain

Question 11

What are the two categories of Configurational Isomers?

Answer 11

Enantiomers and Diastereomers, and they are called Optical Isomers

Question 12

How do you determine CHIRALITY?

Answer 12

If its Mirror Image cannot be superimposed on the original object, meaning the molecule lacks an internal plane of symmetry

Question 13

How do you determine if a carbon atom is Chiral?

Answer 13

If it has FOUR DIFFERENT SUBSTITUENTS

Question 14

Describe the characteristics of enantiomers.

Answer 14

Enantiomers have nearly identical physical properties and chemical properties, but they rotate PLANE-POLARIZED LIGHT in opposite directions (but at Equal magnitudes) and react differently in chiral environments

Question 15

What is a RACEMIC MIXTURE and how does optical activity play a factor with it?

Answer 15

-a racemic mixture is where there are equal parts of both kinds of enantiomers and no optical activity is observed due to each enantiomer’s respective rotation cancelling the other out

Question 16

What is a DIASTEREOMER?

Answer 16

-non-mirror-image configurational isomers
-occur when a molecule has 2 or more stereogenic centers and differs at some, but not all, of these centers
-MUST HAVE multiple chiral centers

Question 17

What is a MESO COMPOUND?

Answer 17

-it is a molecule with chiral centers that has an internal plane of symmetry
-It is thus not optically active

Question 18

How is a molecule designated as the “E” or “Z” form?

Answer 18

-if a molecule has the two highest-priority substituents on the same side of the double bond, it is the Z-form
-if the two highest-priority ones are on opposite sides, it is the E-form

Question 19

How do you determine if a chiral molecule is “R” or “S”?

Answer 19

-number the substituents attached to the chiral center based on their priority
-if the “circle” goes COUNTERCLOCKWISE, it is S
-if the “circle” goes CLOCKWISE, it is R

Question 20

Describe how to assign priority in E/Z naming.

Answer 20

When assigning priority, look only at the first atom attached to the chiral carbon, not at the gorup as a whole. The higher the atomic number of this first atom, the higher the priority-this same system is used to determine the priority for both (E) and (Z) forms, and (R) and (S) forms