Quiz 3 Flashcards
What are the two positions found on a chair conformation?
axial and equitorial
How will you know if an equitorial substituent is up or down?
look at the axial position, if the axial is up the equitorial will be down and vice versa
If a substituent is in an axial down position what position will it be in after a ring flip?
equitorial down
1,3 diaxial interaction
a kind of steric/ gauche interaction that occurs when substituents that are not hydrogens are in axial positions at the same time
True or false?
the larger the substituent the more likely it will be best placed in an axial position?
false, the larger the substiuent the more likely it will want to be placed in an equitorial position
stereoisomerism
molecules that differ in spatial arrangment of groups, not connectivity of atoms
ex: cis/trans isomers
cis isomer
groups exist on the same side
trans isomer
groups exist on opposite sides
constiutional isomer
same formula different connectivity
True or false?
two atoms that are stereoisomers of each other will have the same effects
false, they could have very different effects
what does it mean to be a chiral object?
that you cannot superimpose the mirror image of that object onto the object
ex: hands
Achiral
an object has a plane of symmetry, identical to mirror image and cannot rotate plane of polarized light bc of identical mirror image
chiral center
atom with four different groups attatched
also a stereo center
stereo center
an atom where two of its groups can be swapped and a stereosiomer is formed
How can you identify a stero center that is not also a chiral center?
stereo centers that are not chiral centers will usually be attatched to a double bond
enantiomer
the mirror image of a molecule
A compound can have — enantiomer/s
one
never more and never less
What are the steps for designating R or S configurations?
- find the chiral center
- determine priority of the four groups by numbering 1-4
- rotate the molecule so the lowest priority is going into the plane (dashed)
- Determine after rotation if the groups count counter clockwise (S) or clockwise (R)
How do you determine priority of groups for conformations R and S?
By atomic number
high # = higher priority
low # = lower priority
How do you determine priority if two groups are the same?
look at what they are connected to, first point of priority difference wins
True or false?
A triple bond is only counted once
False, a triple bond will be counted as three single bonds to the atom it is attatched to
Where is the R/S conformation placed when naming the molecule?
at the beginning of the name in parentheses, if there is more than one chiral center the locant comes before the R/S
What does it mean for a molecule to be optically active?
it can rotate a plane of polarized light
True or false?
A chiral molecule is optically active
True, chiral molecules will rotate polarized light
You — use R/S to determine the rotation of a molecule
can not
What are the steps to labeling a diastereomer
E/Z
- assign a priority group on each side of the double bond
- both priority groups on same side = Z
- priority groups on different sides = E
- to be neither E or Z there must be same group on same side of the double bond
Any compound with a — will be achiral
plane of symmetry
what do you do to your total number of predicated stereoisomers if you have a plane of symmetry?
subtract one to account for identical mirror image
If you encoutner two stereocenters on either side of the pi bond how many times should they be counted?
once, becauce you cannot have one without the other
how do you calcualte total number of predicted stereoisomers?
2^n
n = number of chiral centers
Meso compound
achiral compound with two or more chiral centers and a plane of symmetry
