Ochem Exam 2 Flashcards
A molecule with 0 chiral centers is…
A molecule with 1 chiral center is…
0 - achiral
1 - chiral
If a molecule’s chiral centers are all the same configuration, then it is a…
identical molecule
Can a molecule with 1 chiral center have a diastereomer? Why or why not?
No, because if the R/S stays the same it is identical, but if the single R/S changes it is is an enantiomer because “all” the R/S changed.
If a molecule has multiple chiral centers but is overall symmetric, it is a…
meso compound
In a molecule with multiple chiral centers, when all the R/S stay the same then the molecules are…
identical
In a molecule with multiple chiral centers, when all the R/S change then the molecules are…
enantiomers
In a molecule with multiple chiral centers, when only some of the R/S change then the molecules are…
diastereomers
Achiral molecules have a —— mirror image.
superimposable
Chiral molecules have a ——- mirror image.
non superimposable
What is a chiral center?
a carbon with 4 different groups
What are the differences in properties between enantiomers and diastereomers?
enantiomers: some properties except how they interact with chiral things
diastereomers: different properties
What is a racemic mixture?
50/50 mix of enantiomers
When the 4th group is in the back, what direction are the R and S configurations?
clockwise - R
counterclockwise - S
When the 4th group is in the front, what direction are the R and S configurations?
clockwise - S
counterclockwise - R
When you prioritize groups for chiral center configurations, how do you name them?
highest atomic number gets highest priority
if the atom is the same, move out to the first point of difference
What bonds are formed and broken in each of the types of reactions?
substitution - break sigma and form sigma
elimination - break 2 sigma and form a pi
addition - break a pi bond and form 2 sigma
What do the thermodynamics and kinetics tell you about a reacation?
thermodynamics - equilibria/extent/stability
kinetics - rate/speef
What does the Keq tell you about a reaction?
> 1 product favored (exo)
<1 reactant favored (endo)
What does the dH or dG tell you about a reaction?
- product favored (exo)
+ reactant favored (endo)
How do you write the rate equation for a reaction?
SN1 and SN2 specifically
rate=k[reactants of the rate determining step]
SN1 - rate=k[substrate]
SN2 - rate=k[substrate][nucleophile]
The rate determining step is the step with the…
highest transition state
How does activation energy affect the rate of a reaction? How is activation energy affected by catalyst and temperature?
higher Ea = slower
lower Ea = faster
higher temp lowers Ea and increases rate
lower temp increases Ea and slows the rate
SN1 has (1/2) step(s) and (does/does not) have an intermediate
2 step, does have an intermediate
SN2 has (1/2) step(s) and (does/does not) have an intermediate
1 step, does not have an intermediate
What types of substrate are preferred by SN1 and SN2? Why?
SN1 - tertiary, secondary, and primary if it has resonance. Carbocation needs stabilized by the branches.
SN2 - primary, secondary, NEVER tertiary. Needs room for the “backside approach” to happen.
How many structures can be produced from an SN1 reaction? Why?
2, because the Nu can bond at the front or back of the carbocation
In an SN1 reaction, what happens if the 2 structures produced are enantiomers vs diastereomers?
enantiomers - 50/50 racemic mixture
diastereomers - some other mix
What makes a good leaving group?
weak base, pKa less than 16 (generally I-, Br-, Cl-, but NOT F-)
What type of nucleophile is best for a SN1 and SN2 reaction?
SN1 - must be weak, pKa <4.8, as strong/stronger acid form than carboxylic acid (such as O- halogens-, OAc-, acetic acid OO-)
SN2 - good nucleophile, pKa>5 (higher than carboxylic acid)
What type of solvent is preferred by SN1 and SN2?
SN1 - polar protic (contain an OH)
SN2 - polar aprotic
When does inversion occur in an SN2 reaction?
when the backside approach happens on a chiral center
For any elimination reaction to happen, there MUST be…
beta hydrogens
In an elimination reaction, multiple structures called ——– can be produced if…
regioisomers
the beta hydrogens are not equivalent
In an elimination reaction, identical beta hydrogens will produce…
identical products
tetrasubstituted alkenes are —– stable than monosubstituted/not substituted alkenes. Why?
more
More R groups (increased substitution) means more electrons are donated to the double bond area, so it becomes more stable.
Are cis or trans substituted alkenes more stable? Why?
trans, because the groups are farther apart from eachother
