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Flashcards in Isomers Deck (21):
1


What type of strain are staggered conformations lacking?

Staggered conformations have no torsional strain by definition.

2


Define chiral


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

2


Define racemic mixture


A mixture of equal amounts of two enantiomers

3


Define enantiomers


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

4

Define a stereocenter

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

5

Define configuration


Refers to the arragement of atoms about a stereocenter

6


Define conformation


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

7


Define chiral center


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

8


Define Meso compound


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**

9


Define stereoisomers

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)

10

Define configurational isomers


Isomers that differ by the configuration of subsituents on an atom

11


Define Diastereomers

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

12


Define tortional strain


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

13

Define strain


An instability within a structure associated with higher internal energy

15


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

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

16


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

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.

17


Define a constitutional isomer?

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

18

Define achiral

An object that lacks chirality

19


Define angle strain


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

20


Define steric strain


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)

21


Define Isomer


Different compounds with the same molecular formula