2: Isomers: Concept Summary Flashcards
(24 cards)
______ share only a molecular formula (and molecular weight)
Structural/Constitutional Isomers
______ have different physical and chemical properties
Structural/Constitutional Isomers
_______ differ by rotation around a single sigma bond
Conformational Isomers
______ have groups 60 degrees apart, as seen in a Newman Projection
Staggered
_________ have groups directly in front of each other as seen in a Newman Projection.
Eclipsed Conformations
In _____________:
- two largest groups are 180 degrees apart (antiperiplanar)
- the strain is minimized
- lowest energy state
- most energetically favorable type
Anti Staggered
In _______, the two largest groups are 60 degrees apart
gauche staggered
In ________, the two largest groups are directly in front of each other and strain is maximized
totally eclipsed conformations
The strain in cyclic molecules comes from
1) ______ (created by stretching or compressing angles from their normal size)
2) ______ (created from eclipsing conformations)
3) _______ (from interactions between substituents attached to nonadjacent carbons)
* Cyclic molecules will usually adopt nonplanar shapes to minimize this strain
1) angle strain
2) torsional strain
3) nonbonded strain
Substituents attached to cyclohexane can be classified as ___ (sticking up or down from the plane of the molecule) or ______ (in the plane of the molecule).
Axial, equatorial
_____ substituents create more nonbonded strain.
Axial
Larger/bulkier substituents favor the _______ position.
equatorial
(In cyclohexane molecules with multiple substituents, the largest substituents will usually take the equatorial position to minimize the strain)
________ can only be interchanged by breaking and reforming bonds.
Configurational isomers
______ are non superimposable mirror images and thus have opposite stereochemistry at every chiral carbon. They have the same chemical and physical properties except for rotation of plane polarized light and reactions in a chiral environment.
Enantiomers
______ refers to the ability of a molecule to roate plane-polarized light: d- or (+) molecules rotate light to the right;
l- or (-) molecules rotate light to the left
Optical activity
_______, with equal concentrations of two enantiomers, will not be optically active the two enantiomers’ rotations cancel each other out
Racemic Mixtures
_______, with an internal plane of symmetry, will also be optically inactive because the two sides of the molecule cancel each other out
Meso compounds
_______ are non-mirror-image stereoisomers.
They differ at some, but not all, chiral centers.
They have different chemical and physical properties.
*May react similarly in particular reactions because they have the same functional groups
Diastereomers
_____ isomers are a subtype of diastereomers in which groups differ in position about an immovable bond (such as a double bond or in a cycloalkane)
Cis-trans
_____ have four different groups attached to the central carbon
Chiral Centers
_______ gives the stereochemistry of a compound in comparison to another molecule
Relative Configuration
________ gives the stereochemistry of a compound without having to compare to other molecules
Absolute Configuration
Absolute configuration uses the Cahn-Ingold-Prelog priority rules: priority is given by looking at the atoms connected to the chrial carbon or double-bonded carbons; whichever has the highest atomic number gets highest priority. If there is a tie, one moves outward from the chiral carbon or double-bonded carbon until the tie is broken
An alkene is (__) if the highest-priority substituents are on the same side
Z
“Ze Zame Zide”
An alkene is (__) if the highest-priority substituents are on opposite sides
E
“Epposite Sides”
