CHEM 233 EXAM 2 (2026/2027) QUESTIONS
AND CORRECT ANSWERS GRADED A+
what happens when we mix pyridinium tribromide and acetic acid?
we form pyridinium bromide and molecular bromine where the equilibrium for this
reaction favors the left side (pyridinium bromide)
what does this mean?
we only have a small amount of molecular bromine
if we have a small amount of molecular bromine will the reaction be slow?
no because of Le Chatelier's principle where if we use molecular bromine in the
bromination reaction the equilibrium reaction has to shift to the right to make more
bromine
what alkene do we use?
tranexamic acid
by what mechanisms can this bromination reaction occur?
1. anti addition
2. syn addition
3. mixture
,how do we differentiate what mechanism occurred?
we look at the products stereochemistry because each mechanism produces
different stereochemistry
steps of the procedure
1. dissolve tranexamic acid in acetic acid
2. slowly heat till dissolved
3. add pyridinium tribromide and boil for 15 minutes
4. cool to precipitate product out
5. collect product via vacuum filtration
6. MP analysis
why do we do a MP analysis?
because each product has a different MP range
-anti has 202-204C
-syn 93.5-95C
why do the anti and syn additions have different MPs?
because they are diastereomers and diastereomers have different MPs
,why dont we see a MP depression when we have a product and its enantiomer?
enantiomers of products do not act like impurities
percent yield
actual yield/theoretical yield
to find the % yield we have to know the
limiting reagent (reactant that is used up first)
in this lab we find
the limiting reagent and % yield
A is the limiting reagent and 1 mol C is the theoretical yield
the reagent with the least number of mols
is NOT always the limiting reagent because of stoichiometry (must balance the
reaction)
B is the limiting reagent and 0.5 mol C is the theoretical yield
, mass (grams) to mols
mass of compound/molecular weight of compound
How can we view intermediates before they disappear?
-IR spec or NMR spec
-kinetics to see how changing the concentrations affects the rate of the reaction
if we have two different mechanisms (product distribution) that are not known, we
can determine what one occurred (was operative) by
identifying the product
alkenes and phenyl rings undergo
different chemical reactions
what happens in a bromination?
you have some alkene and bromine is added to either side of it via addition
what solvent are we using?
acetic acid because acid helps accelerate the reaction
AND CORRECT ANSWERS GRADED A+
what happens when we mix pyridinium tribromide and acetic acid?
we form pyridinium bromide and molecular bromine where the equilibrium for this
reaction favors the left side (pyridinium bromide)
what does this mean?
we only have a small amount of molecular bromine
if we have a small amount of molecular bromine will the reaction be slow?
no because of Le Chatelier's principle where if we use molecular bromine in the
bromination reaction the equilibrium reaction has to shift to the right to make more
bromine
what alkene do we use?
tranexamic acid
by what mechanisms can this bromination reaction occur?
1. anti addition
2. syn addition
3. mixture
,how do we differentiate what mechanism occurred?
we look at the products stereochemistry because each mechanism produces
different stereochemistry
steps of the procedure
1. dissolve tranexamic acid in acetic acid
2. slowly heat till dissolved
3. add pyridinium tribromide and boil for 15 minutes
4. cool to precipitate product out
5. collect product via vacuum filtration
6. MP analysis
why do we do a MP analysis?
because each product has a different MP range
-anti has 202-204C
-syn 93.5-95C
why do the anti and syn additions have different MPs?
because they are diastereomers and diastereomers have different MPs
,why dont we see a MP depression when we have a product and its enantiomer?
enantiomers of products do not act like impurities
percent yield
actual yield/theoretical yield
to find the % yield we have to know the
limiting reagent (reactant that is used up first)
in this lab we find
the limiting reagent and % yield
A is the limiting reagent and 1 mol C is the theoretical yield
the reagent with the least number of mols
is NOT always the limiting reagent because of stoichiometry (must balance the
reaction)
B is the limiting reagent and 0.5 mol C is the theoretical yield
, mass (grams) to mols
mass of compound/molecular weight of compound
How can we view intermediates before they disappear?
-IR spec or NMR spec
-kinetics to see how changing the concentrations affects the rate of the reaction
if we have two different mechanisms (product distribution) that are not known, we
can determine what one occurred (was operative) by
identifying the product
alkenes and phenyl rings undergo
different chemical reactions
what happens in a bromination?
you have some alkene and bromine is added to either side of it via addition
what solvent are we using?
acetic acid because acid helps accelerate the reaction
