9b Flashcards
whats something we were taught could happen in benzene but it cant rlly,, and explain why it cant happen
u cannot form a cation on benzene.
theres empty p orbitals on each carbon,, and an empty sp2 orbital.
the pi system (all the p orbitals pointing up) is orthogonal to the empty sp2 orbital that points to the side of the molecule
bc theyre orthogonal, they dont overlap,, meaning e- cannot go into the empty sp2 ,, THERES NO RESONANCE STABILISATION.
what is the worlds best lg
N2
N triple bond N
theres a + charge on the first N
how can we make a cation on a benzene
we can use N2 (N+ triple N)
this is a rlly good lg so it can leave and leave an empty sp2 orbital on the benzene
this cannot be stabilised with resonance using the other p orbitals bc theyre orthogonal to eachother, meaning they cant overlap
is a benzene with a cation unstable or stable
extremely unstable
how do u make a diazonium salt
no2 + H to protonate the O
kick off h20 to give NtripleO+
Nh2 bonds to NtripleO
O is protonated, H is removed
last H is used to kick off H20 and form NtripleN
the R group of the amine used to make a diazonium salt is what
is the R group bonded to the diazonium salt once it is made.
what do diazonium salts contain
they contain the rlly good NtripleN leaving group
do aliphatic diazonium salts react immediately
yes,, things with the diazonium group react immediately to give a range of different products
whats an aryldiazonium salt
when u have benzene and the diazonium NtripleN is bonded to it
the NtripleN usually has a Cl near it bc its a salt
whats a cuprous salt
a Cu with a halogen or CN bonded to it
what does a aryldiazonium salt and a cuprous salt give u
the diazonium salt is a rlly good lg so is removed super quickly.
the substituent on the Cu is then bonded to where the diazonium salt is.
sandmayer reaction
aryldiazonium salt (benzene with NtripleN)
with cuprous salt (CuX)
the X goes where the diazonium salt was bonded on the benzene
going from benzene to ben-X
- benzene + no3 = nitro benzene
- then reduce it to make NH2
- then add no2 to form NtripleN
- then add CuX,, where X can be Cl, Br or CN (copper salts)
forming diazonium salts
no2 and amine
so sandmayer is the diazonium salt addition one,, is it more like sn1 or sn2
sn1
bc theres 2 steps
loss of lg (n2)
addition of other group
there is a cc+ intermediate once the n2 is removed
do only copper salts work
nope
the OH and I also work
aryldiazonium and water adds OH
aryldiazonium and KI adds I
any anion can be added tbh
okay if we have a NH2 on a benzene and we want to remove it,, how would we do this
NH2 and NO2 to form a diazonium salt (very good lg)
then use H3PO2 to add a H to the CC+
youve removed the group!!
remember its the R group on the amine that stays in the product!!
precise way of going from amine to diazonium fg
NaNO2
HCl
forms a diazonium salt (+) and the Cl (-)
how do we reduce benzene to cyclohexane
we use high pressure H2 for hydrogenation (100atm)
and a metal catalyst : Pt, Rh, Ni for aromatic hydrocarbons (arenens)
when we reduce benzene to cyclohexane,, other substituents can survive without being reduced,, what conditions do this
100 atm H2,, Ni, Rh, Pt catalyst
benxene to cyclohexane,, what is lost
aromaticity,, thats why we need harsher conditions for this to occur
once one benzene double bond is reduced,,, why do the other bonds get reduced much faster
bc aromaticity would have been lost after the first double bond was removed,, so the ring is no longer aromartic meaning it doesnt have the extra stability.
