4/18/2024 Flashcards
if the energy of the products is less than the reactants what is the ∆G
it is negative and a spontaneous reaction
what is the pka for a terminal alkyne and what does it mean
the pka is 25, meaning it is acidic enough to undergo deprotonation
what is alkylation
the process of creating a new carbon carbon bond
what is alkylation best performed with?
acetylide ion (carbanion intermediate) and a primary or methyl alkyl halide.
what happens if you try to perform alkylation with a secondary or tertiary alkyl halide?
the mechanism will occur through an E2 pathway which will lead to an unproductive formation of an alkene
what is an acetylide
it is the carbanion intermediate that forms when a terminal alkyne is deprotonated
it can act as a nucleophile and is electron rich
why is the production of an alkene through the use of a acetylide ion and a secondary/tertiary alkyl halide unproductive?
it’s unproductive because if we wanted an alkene we should have used a less expensive base rather than an acetylide ion
why shouldn’t you use an acetylide ion with a secondary or tertiary alkyl halide if the goal is to make an alkylation?
if you use a secondary or tertiary, the acetylide ion would rather act as a base (steric effect) and preform an E2 reaction which would result in an alkene rather than an alkylation
what is hydrogenation
it is the reduction of an alkene to an alkane through the addition of two hydrogen atoms across a double bond.
what are catalysts used for in a hydrogenation process?
they help speed up the reaction by lowering the activation energy and help deliver the hydrogens to either side of the double bond on the alkene
if we subject an alkyne to hydrogenation, what will happen? will it stop at the alkene?
no, the reaction will proceed all the way until it becomes an alkene
how can we stop an alkyne from continuing the hydrogenation past the alkene?
we can use a poison catalyst to slow it down
if we react an alkyne with Lindars catalyst, what will form?
a cis alkene
why do we only get the cis alkene when using lindars catalyst
lindars catalyst prevents rotation of the molecule, this forces the H2 to be added to the same side of the molecule, resulting in a cis alkene
What do we use when we want to stop a hydrogenation reaction with an alkyne?
you can use lindars catalyst to form a cis alkene
what is a dissolving metal reduction
it is the use of 2 lithium or sodium metal in ammonia or ethylamine at low temperatures to produce a trans alkene.
what is retrosynthetic analysis
working backward from the target molecule to the synthesis required
if you have an asymmetric alkene, where was the carbocation form
more subst
if you have an asymmetric alkene, where does the carbocation form
the tertiary
what is markovnikovs rule
it is when the hydrogen atom adds to the carbon atom of the double bond that has the most number of hydrogens
what does a dissolving metal reduction result in
trans alkene
what does a reaction with lindars catalyst result in
cis alkene
what is an electrophillic addition
you take an alkene and react it with a halogen, this results in an alkyl halide
what is a hydration
it is where we treat an alkene with h20 and an aqueous acid to form an alcohol
in an electrophillic addition, what is the nucleophile?
the electron density in the double bond serves as the nucleophile while the polar bond between a halogen and a hydrogen serves as the electrophile
why does the H-X act as an electrophile in an electrophilic addition?
the H-X is a polar covalent where the H is a electrophilic center
what is a stereo selective reaction
A stereoselective reaction is a reaction that prefers a specific stereoisomer over another.
what is a regioselective reaction
Any process that favors bond formation at a particular atom over other possible atoms
what is a syn addition
it is when we place parts of the adding reagent on the same side of the reactant
when we add H2 on a lindars catalyst to a alkyne, what is the product
this results in a syn addition and the formation of a cis (typically Z) alkene
what is an anti addition
it is when the parts of the added reagent are added on opposite sides of the reactant
what is an anti addition of hydrogen to an alkyne
it is when a trans or E alkene is formed as a result of a dissolving metal reduction
When deprotonating a terminal alkyne with NaNH2, what is formed that drives the reaction forward?
the formation of NH3 which is very stable
what is the purpose of the lithium in a dissolving metal reduction
it acts as a source of electrons
what is the purpose of the ethylammine in a dissolving metal reduction
it acts as a source of protons
what are the three ways to reduce an alkyne
you can use an H2/Pt or Pd Catalyst to preform hydrogenation and form an alkane
you can use Lindar’s Catalyst to form a cis alkene
you can use 2Li, 2 ethylammine in ammonia chloride to form a trans alkene
if you reduce an alkyne with lindars catalyst, what is the product
a cis alkene
if you reduce an alkyne with 2 Li, 2 ethylammine in ammonia chloride, what do you get
a trans alkene
if you subject an alkyne to an H2/Pt catalyst, what will the product be
an alkane
