Chapter 2: Isomers Flashcards
What causes ring strain?
Angle strain, torsional strain, non-bonded strain/steric strain
What causes angle strain?
When bond angles are stretched or compressed from their normal size
What causes torsional strain?
When cyclic molecules must assume conformations that have eclipsed or gauche interctions
What causes non-bonded/steric strain?
When nonadjacent groups or atoms compete for the same space
Define structural isomers & describe if they share physical/chemical properties
Isomers that share only a molecular formula and have different physical and chemical properties
Define conformational isomers
Isomers that differ by rotation around a single bond
Define staggered conformations of conformational isomers and the two subtypes
Have groups 60 degrees apart; subtypes are anti-staggered (180 degrees apart) and gauche staggered (60 degrees apart)
Define eclipsed conformations of conformational isomers
Groups directly in front of each other as per Newman projections
Which creates more non-bonded strain: axial or equatorial substituent positions
Axial
In cyclohexane molecules with multiple substituents, the largest substituent will usually take up the ___________ position
Equatorial
Define configurational isomers
Isomers that can only be interchanged by breaking and reforming bonds
Define enantiomers and do they share physical/chemical properties
Enantiomers are non-superimposable mirror images (i.e., opposite stereochemistry at every chiral carbon); they share the same chemical and physical properties except for rotation of plane-polarized light and rxns in chiral environments
Define optical activity
The ability of a molecule to rotate plane-polarized light
D- molecules are also known as (__) and rotate light to the ______
(+); right
L- molecules are also known as (__) and rotate light to the _______
(-); left
Define racemic mixtures
Mixture with equal concentrations of two enantiomers; not optically active b/c enantiomers cancel each other out
Define meso compounds
Compounds with chiral centres but an internal plane of symmetry that makes it optically inactive
Define diastereomers and do they share chemical/physical properties
non mirror-image stereoisomers that differ at some but not all chiral centres. They have different chemical and physical properties
Define cis-trans isomers
Subtype of diastereomers in which groups differ in position about an immovable bond (i.e., double bond or cycloalkane)
Define relative configuration
Gives the stereochemistry of a compound in comparison to another molecule
Define absolute configuration
Gives the stereochemistry of a compound without having to compare to other molecules
An alkene is (Z) if the highest-priority substituents are on the ______ side of the double bond
Same
An alkene is (E) if the highest-priority substituents are on the ______ side of the double bond
Opposite
Switching one pair of substituents on a Fischer diagram…..
Inverts the stereochemistry of the chiral centre
