Chem 234 Lab Final exam with correct
answers
another |name |for |Diels-alder |reaction |- |correct |answers✔✔[4 |+ |2] |cycloaddition
why |must |dicyclopentadiene |must |be |cracked? |- |correct |answers✔✔because |it
|cyclopentadiene |dimerizes |with |itself |at |room |temp |to |form |dicyclopentadiene |which
|is |not |reactive |as |a |diene |in |a |Diels-Alder |reaction. |Heating |dicylcopentadiene
|results |in |a |reto |diels-alder |reaction |to |provide |cyclopentadiene.
why |should |you |not |put |a |standard |thermometer |when |the |product |is |cracking? |-
|correct |answers✔✔the |temp |of |the |reaction |should |be |about |300 |degrees |and |a
|normal |thermometer |would |explode |because |it |would |reach |past |the |heating |limit.
explain |why |s-trans |conformation |predominates |at |room |temp |- |correct
|answers✔✔because |there |is |bad |steric |interaction |between |the |two |alkene |hydrogen
|in |the |s-cis |conformation
what |solvent |will |you |use |to |recrystallize |the |three |products |you |obtain |following |the
|aromatic |substitution |reactions? |- |correct |answers✔✔ethanol
unactivated |aromatic |compounds |such |as |benzene |will |not |undergo |electrophillic
|aromatic |substitution |w/ |bromine |alone. |what |could |you |add |to |the |reaction
|mixture |to |facilitate |the |reaction. |- |correct |answers✔✔add |a |lewis |acid |such |as
|FeBr3
mixing |HNO3 |and |H2SO4 |to |generate |the |active |electrophile, |which |is? |- |correct
|answers✔✔NO2+
what |is |the |purpose |of |the |acetic |acid |used |in |the |experiment? |- |correct
|answers✔✔it |is |merely |a |solvent
, what |is |the |commercial |use |of |the |methyl |red? |- |correct |answers✔✔Acid/base
|indicator, |synthetic |dye
why |is |it |important |to |keep |the |diazonium |salt |cool |after |you |prepare |it? |- |correct
|answers✔✔at |room |temp |it |will |prematurely |decompose |through |a |process |that
|involves |the |evolution |of |nitrogen |gas.
describe |how |a |typical |grignard |reagent |(PhMgBr) |is |prepared |- |correct
|answers✔✔adding |a |vinyl |halide |or |aryl |halide |to |magnesium |metal |will |result |in
|the |magnesium |adding |between |the |Ph |and |Br |to |form |the |Grignard |reagent
|(PhMgBr). |this |process |is |an |oxidation |addition
why |is |it |critical |that |the |reaction |and |solvents |be |free |from |any |residual |water? |-
|correct |answers✔✔water |will |destroy |the |Grignard |reagent |(reaction |proves |it) |
R-MgBr |+ |H-OH |= |R-H |+(HO)MgBr
in |the |addition |to |to |water, |oxygen |will |also |hinder |a |Grignard |reaction. |Explain |how
|you |will |keep |the |reaction |apparatus |free |of |oxygen. |- |correct |answers✔✔the
|reaction |apparatus |will |be |flushed |with |dry |nitrogen |and |maintained |under |this
|atmosphere |throughout |the |reaction
other |than |Na2Cr2O7 |what |could |preform |a |reaction? |- |correct |answers✔✔K2Cr2O7
|or |KMnO4
what |is |the |purpose |of |adding |ethanol |to |the |reaction |mixture |following |the |reaction
|between |para-nitrotoluene |and |sodium |dichromate? |- |correct |answers✔✔the |ethanol
|reduces |excess |Cr(VI) |to |Cr(III) |and |get |oxidized |to |acetic |acid |in |the |process
why |is |it |necessary |to |use |extra |precaution |when |handling |chromium |(VI) |salts |such
|as |Na2Cr2O7 |? |- |correct |answers✔✔Chromium |salts |are |toxic, |AND |specifically |they
|are |carcinogenic
why |is |the |large |excess |of |acetic |acid |necessary |for |the |above |reaction |to |proceed? |-
|correct |answers✔✔the |esterification |is |an |equilibrium |process |so |you |need |to |either
answers
another |name |for |Diels-alder |reaction |- |correct |answers✔✔[4 |+ |2] |cycloaddition
why |must |dicyclopentadiene |must |be |cracked? |- |correct |answers✔✔because |it
|cyclopentadiene |dimerizes |with |itself |at |room |temp |to |form |dicyclopentadiene |which
|is |not |reactive |as |a |diene |in |a |Diels-Alder |reaction. |Heating |dicylcopentadiene
|results |in |a |reto |diels-alder |reaction |to |provide |cyclopentadiene.
why |should |you |not |put |a |standard |thermometer |when |the |product |is |cracking? |-
|correct |answers✔✔the |temp |of |the |reaction |should |be |about |300 |degrees |and |a
|normal |thermometer |would |explode |because |it |would |reach |past |the |heating |limit.
explain |why |s-trans |conformation |predominates |at |room |temp |- |correct
|answers✔✔because |there |is |bad |steric |interaction |between |the |two |alkene |hydrogen
|in |the |s-cis |conformation
what |solvent |will |you |use |to |recrystallize |the |three |products |you |obtain |following |the
|aromatic |substitution |reactions? |- |correct |answers✔✔ethanol
unactivated |aromatic |compounds |such |as |benzene |will |not |undergo |electrophillic
|aromatic |substitution |w/ |bromine |alone. |what |could |you |add |to |the |reaction
|mixture |to |facilitate |the |reaction. |- |correct |answers✔✔add |a |lewis |acid |such |as
|FeBr3
mixing |HNO3 |and |H2SO4 |to |generate |the |active |electrophile, |which |is? |- |correct
|answers✔✔NO2+
what |is |the |purpose |of |the |acetic |acid |used |in |the |experiment? |- |correct
|answers✔✔it |is |merely |a |solvent
, what |is |the |commercial |use |of |the |methyl |red? |- |correct |answers✔✔Acid/base
|indicator, |synthetic |dye
why |is |it |important |to |keep |the |diazonium |salt |cool |after |you |prepare |it? |- |correct
|answers✔✔at |room |temp |it |will |prematurely |decompose |through |a |process |that
|involves |the |evolution |of |nitrogen |gas.
describe |how |a |typical |grignard |reagent |(PhMgBr) |is |prepared |- |correct
|answers✔✔adding |a |vinyl |halide |or |aryl |halide |to |magnesium |metal |will |result |in
|the |magnesium |adding |between |the |Ph |and |Br |to |form |the |Grignard |reagent
|(PhMgBr). |this |process |is |an |oxidation |addition
why |is |it |critical |that |the |reaction |and |solvents |be |free |from |any |residual |water? |-
|correct |answers✔✔water |will |destroy |the |Grignard |reagent |(reaction |proves |it) |
R-MgBr |+ |H-OH |= |R-H |+(HO)MgBr
in |the |addition |to |to |water, |oxygen |will |also |hinder |a |Grignard |reaction. |Explain |how
|you |will |keep |the |reaction |apparatus |free |of |oxygen. |- |correct |answers✔✔the
|reaction |apparatus |will |be |flushed |with |dry |nitrogen |and |maintained |under |this
|atmosphere |throughout |the |reaction
other |than |Na2Cr2O7 |what |could |preform |a |reaction? |- |correct |answers✔✔K2Cr2O7
|or |KMnO4
what |is |the |purpose |of |adding |ethanol |to |the |reaction |mixture |following |the |reaction
|between |para-nitrotoluene |and |sodium |dichromate? |- |correct |answers✔✔the |ethanol
|reduces |excess |Cr(VI) |to |Cr(III) |and |get |oxidized |to |acetic |acid |in |the |process
why |is |it |necessary |to |use |extra |precaution |when |handling |chromium |(VI) |salts |such
|as |Na2Cr2O7 |? |- |correct |answers✔✔Chromium |salts |are |toxic, |AND |specifically |they
|are |carcinogenic
why |is |the |large |excess |of |acetic |acid |necessary |for |the |above |reaction |to |proceed? |-
|correct |answers✔✔the |esterification |is |an |equilibrium |process |so |you |need |to |either
