10/1 Flashcards
what is the gringard reagent characterized by?
a carbon magnesium bond that reverses polarity and creates a carbocation like molecule that can act as a nucleophile and a base
how are organolithium and the gringard reaction similar
they have the same mechanistic pathway and both act as nucleophiles
what is needed to form an organo lithium
an alkyl halide, 2 equivalents of lithium, and and ether solvent like Et2O (Diethyl Ether)
what is the order of reactivity for alkyl halides to make grignards or organolithiums
RI>RBr>RCl
what is it called when the halogen is exchanged with magnesium in an alkyl halide
magnesium halogen exchange
what solvents do you use in grignard reagents?
ether (diethyl ether Et2O), THF, or hexane
do not use water or polarprotic solvents as it can undergo acid base chemistry
why can you not use grignards or organolithium’s in a water solvent
Grignard reagents are nucleophilic and basic so they can undergo strongly favored acid-base chemistry
what is the dual nature of nucleophiles
they can be nucleophilic and basic
which way will equilibrium lie in an acid base reaction with an organometallic and water
it will favor the formation of the weaker acid, which is R-H and OH
how does an aldehyde and ketone react with a Grignard reagent?
it undergoes nucleophilic addition once to create an alcohol
how does an ester react with a grignard
it reacts with two equivalents to form a tertiary alchohol
what are good sources of protons for the protonation of an alkoxide ion
H3O+ or NH4Cl
if you have a carbonyl and an alcohol on a chain, how can you isolate it so the organometallic nucleophile will attack the carbonyl and not deprotonate the alcohol
use a protecting group like TBSCl
what is a conjugated system
they are molecules where there is a chain of alternating single and double bonds that allows for the delocalization of pi electrons across overlapping p-orbitals
what are the features of a conjugated system
each carbon is sp2 and there is a p-orbital above and below the plane that allows electrons to be delocalized as the electron density can be evenly shared throughout
what is a spacer carbon
it is a sp3 carbon in between two pi bonds that interrupts the conjugated system, the electrons are localized and this is an nonconjugated system
what is considered a conjugated system
a system with sp2 carbons in an uninterrupted array
what is an allyl radical, is it conjugated
it is a radical, next to a double bond. It is conjugated because all the carbons are sp2
what is an allyl cation? Is it conjugated
an allyl cation is a carbocation next to a double bond, it is conjugated because all carbons are sp2
whats an enyne
it is a conjugated alkyne
can sp carbons have conjugation
yes
when reacting an alkene with a halogen X2 in low temperatures, what occurs
electrophillic addition
when reacting an alkene with a halogen X2 in a high temperatures, what is the result
a radical substitution where the allylic hydrogen is replaced with a halogen
what pathway does an allylic substitution go through
under high temperatures, allylic substitution of the hydrogen on an allylic carbon is replaced with a halogen through a radical mechanism with a allylic radical
what is the order of stability for a radical
allylic radicals are the most stable
3>2>1
vinyl radicals are the least stable
why is it better to use NBS to preform allylic substitution rather than Br2 or Cl2
it is a solid while Bromide and Chlorine are liquid and gas.
It also gives you the desired product
what is needed to preform allylic bromination on propene
NBS serves as a source of bromine radical, hv (light), and peroxides which serve as a radical initiator
