Isomers Flashcards
What type of strain are staggered conformations lacking?
Staggered conformations have no torsional strain by definition.
Define chiral
From the greek word for hand, an object that is not superimposable on its mirror image. Essentially an object that has “handedness”
Define racemic mixture
A mixture of equal amounts of two enantiomers
Define enantiomers
Stereoisomers that are non-superimposable mirror images of each other; refers to a relationship between pairs of objects
Define a stereocenter
An atom, most commonly carbon, about which exchage of two groups produces a different stereoisomer (eg. cis v. trans)
Define configuration
Refers to the arragement of atoms about a stereocenter
Define conformation
Any three-dimensional arrangement of atoms in a molecule that results from rotation about a single bond (ex. staggered, eclipse)
Define chiral center
A tetrahedral atom, most commonly carbon, that is bonded to four different groups (a type of stereocenter)
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**
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)
Define configurational isomers
Isomers that differ by the configuration of subsituents on an atom
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
Define tortional strain
Strain that arises when non-bonded atoms separated by three bonds are forms from a staggered conformation to an eclipsed conformation
Define strain
An instability within a structure associated with higher internal energy
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
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.
- Count the number of central atoms: 1,1,1,2,3,5,9
- Start with all atoms in a line
- 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)
- For larger branches, break into substituents. For example, ethyl branch can also be two methyl branches.
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
Define achiral
An object that lacks chirality
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)
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)
Define Isomer
Different compounds with the same molecular formula
