Ch. 6 Flashcards
(45 cards)
what is nucleophilic substitution , what bond gets broken?
where a leaving group on an electrophile gets replaced by a nucleophile. the sigma bond gets broken
for an SN2 rxn, what are the usual substrates used? what is the substrate?
the usual substrates used are alkyl halides because the halides are stable when alone. the substrate is an electrophile
how does nucleophile attack in the SN2 rxn? timing of the attack?
the nuc attacks the carbon at the same time the halide leaves and it is a backside attack.
what is an important part of the nuc attack in an sn2 rxn?
it inverts the carbon that it is attacking
sn2 rxns are what-molecular? what is the reaction dependent on?
sn2 rxns are bimolecular and they are dependent on the conc of both the nuc and the elctro
what kind of substrate is preferred for an SN2 rxn? why?
a methyl compound. if it is bulkier, it will harder for the nuc to reach the carbon
what kind of solution is favored for an SN2 rxn?
a polar aprotic (non h bonding) solvent
in an sn1 rxn, what is important to note about the mechanism of this rxn?
it creates a carbocation intermediate
what is the stability trend for a carbocation
tertiary carbon is most stable while methyl is least stable
how many steps are there in an SN1 reaction? in an SN2? why?
SN1: two steps nuc attacks, a carbocation is formed and nuc attacks on either side of pi bond
SN2: one step, nuc attacks at same time halide leaves
what are the two steps for SN1 rxns?
1) halides leaves and creates a carbocation of 120 degrees, this is the rate limiting step
2) the nuc will attack on either side of the carbon making a racemic mix
what is important about the products of an SN1 rxn?
there is 50% one product and 50% of another
SN1 rxns are what molecular? what does this rxn depend on?
it is unimolecular. it is dependent on the electrophile.
what is the substrate preferred for SN1 rxns?
bulky tertiary because of the carbocation
what kind of solvent is used for SN1 rxns?
protic
what kind of nuc is favored in sn one reaction?
non basic weak nuc
how do alcohols react in SN1 and SN2 rxns?
the hydroxyl group must be protonated to make it a good leaving group. in SN2 rxns, conjugate base will attack carbon while in SN1, water or halide attacks
oxidizing an alcohol produces what? specific the kind of alcohol, the oxidizing agent, and the result of the rxn.
primary alcohols turn into an aldehyde with PCC.
secondary alcohols turn into a ketone with Cro3
tertiary alcohols do not react because no open hydrogen
what is an oxidizing agent?
something that gets reduced, therefore takes electrons
what are some hydride oxidants? what do they do to alcohols?
most with chromium (H2CrO4, Cr ₂O²⁻, Cr03) and permanganate (MnO4-) . they are strong oxidants, therefore will make an alcohol into a carb acid
what are some anhydride oxidants? what do they do to alcohols
PCC
what does a C=O bond do to electron density
the oxygen will pull electron density towards it making the carbon slightly positive, making it good to be attacked by nuc
protons that are near EN atoms or bonds will become
very acid, a proton near a carbonyl group will be more acidic than a hydrogen near an hydroxy group
how does an acidic hydrogen gets removed by what? what is the result of this occurring with a carbonyl?
removed by a strong base, it will become an enolate ion (-) O, very negative and good nuc
