Isomers

Question 1

What type of strain are staggered conformations lacking?

Answer 1

Staggered conformations have no torsional strain by definition.

Question 2

Define chiral

Answer 2

From the greek word for hand, an object that is not superimposable on its mirror image. Essentially an object that has “handedness”

Question 2

Define racemic mixture

Answer 2

A mixture of equal amounts of two enantiomers

Question 3

Define enantiomers

Answer 3

Stereoisomers that are non-superimposable mirror images of each other; refers to a relationship between pairs of objects

Question 4

Define a stereocenter

Answer 4

An atom, most commonly carbon, about which exchage of two groups produces a different stereoisomer (eg. cis v. trans)

Question 5

Define configuration

Answer 5

Refers to the arragement of atoms about a stereocenter

Question 6

Define conformation

Answer 6

Any three-dimensional arrangement of atoms in a molecule that results from rotation about a single bond (ex. staggered, eclipse)

Question 7

Define chiral center

Answer 7

A tetrahedral atom, most commonly carbon, that is bonded to four different groups (a type of stereocenter)

Question 8

Define Meso compound

Answer 8

An achiral compound posessing two or more chiral centers that also has chiral isomers, but whose mirror image is identical to the compound

**will posess a plane of symmetry**

Question 9

Define stereoisomers

Answer 9

Stereoisomers are compounds that have the same molecular formula, the same connectivity of their atoms, but a different orientation of their atoms in space (ex. cis and trans)

Question 10

Define configurational isomers

Answer 10

Isomers that differ by the configuration of subsituents on an atom

Question 11

Define Diastereomers

Answer 11

Stereoisomers that are not mirror images of each other; refers to relationships among two or more objects

*Requires at least two chiral centers to have diastereomers

Question 12

Define tortional strain

Answer 12

Strain that arises when non-bonded atoms separated by three bonds are forms from a staggered conformation to an eclipsed conformation

Question 13

Define strain

Answer 13

An instability within a structure associated with higher internal energy

Question 15

Given a structure, how do you determine if it is a constitutional isomer?

Answer 15

Constitutional isomers are compounds that have the same molecular formula but different structural formulas.

• Determine each structure’s molecular formula. Are they equal?
  a. ) If not equal, NO
  b. ) If equal:
• Exact same structure? -> Identical
• Different structure? -> YES

Question 16

Given a formula, how do you draw all possible constitutional isomers?

Answer 16

Constitutional isomers are compounds that have the same molecular formula but different structural formulas.

1. Count the number of central atoms: 1,1,1,2,3,5,9
2. Start with all atoms in a line
3. Reduce by one central atom. Add the branch to the # of central atoms +1 or greater (e.g. methyl branch can be added to carbon 2 or greater)
4. For larger branches, break into substituents. For example, ethyl branch can also be two methyl branches.

Question 17

Define a constitutional isomer?

Answer 17

Constitutional isomers are compounds that have the same molecular formula but different structural formulas.

• Differ in type of bonds they have (single, double, triple) and/or
• Differ in connectivity of their atoms

Question 18

Define achiral

Answer 18

An object that lacks chirality

Question 19

Define angle strain

Answer 19

Angle strain is the strain that arises when a bond angle is either compressed or expanded compared to its optimal value (109.5 degrees)

Question 20

Define steric strain

Answer 20

Steric strain arises when non-bonded atoms separated by four or more bonds are forced closer to each other than their atomic radii would allow. (i.e. strain between large groups)

Question 21

Define Isomer

Answer 21

Different compounds with the same molecular formula