ORGO Ch. 2 Isomer Flashcards
What is a conformational isomer?
same molecules that differ around the single bond
What is gauche staggered conformation?
methyl groups are 60 degrees apart
What is eclipse conformation?
methyl groups are 120 degrees apart
Which is the least genetically favorable conformation?
totally eclipsed - 2 largest groups are on the same plane on the same side
Which is the most genetically favorable conformation?
anti staggered - 2 largest groups are on the same plane but on opposite sides
What are the 3 factors that create ring strain?
angle strain, torsional strain, and nonbonded strain/steric
What causes angle ring strain?
when bonded angels are stretched or compressed
What causes torsional ring strain?
results when cyclic molecules must assume eclipse of gauche conformation
What causes nonbonded ring strain?
results when nonadjacent atoms or groups compete for the same space
What are the 3 envelope conformations of cyclohexane?
chain, boat, or skew-boat
What is the most stable conformation of cyclohexane?
chair conformation
What are the 2 configurational isomers?
diastereomers and enantiomers
What is the diff b/w diastereomers and enantiomers?
enantiomers are non-superimposable mirror images with opposite stereochemistry at every chiral carbon, diastereomers are not mirrored images of each other with different chemical and physical properties
What happens in racemic mixtures?
+ and - enantiomers are presented in equal concentration, thus the rotations cancel each other out, and there is no optical activity observed
What is the diff b/w cis and trans isomers?
cis - 2 substituents are on the same side of the immovable bond
trans - 2 substituents are on opposite sides of the immovable bond
What are the criteria for a molecule to have optical activity?
they must have a chiral center, and lack a plane of symmetry
What is a mesocompound?
a molecule with chiral centers that has an internal plane of symmetry
How is priority in E and Z determined?
priority is assigned based on the atom bonded to the double bond; the higher the atomic number, the higher the priority
What is the diff b/w E and Z forms?
The alkene is named Z if the 2 highest priority substituents on each carbon are on the same side of the double bond, and E if they are on opposite sides
What is the diff b/w R and S forms?
R = clockwise - right turn from highest to lowest priority
S = counterclockwise - left turn from highest to lowest priority molecule
In Fischer’s projections, what is the direction of the lowest priority group?
the lowest priority groups project in to the page
What is anti-staggered conformation?
methyl groups are 180 degrees apart
What position creates less strain in a cyclohexane molecule?
equatorial
