organic 7 Flashcards
double bonds cant do what
double bonds cant rotate
what does P love bonding to
P likes bonding to O
the witting reaction forms what
the witting reaction forms double bonds
witting reaction steps:
bromo cyclohexane + PPh3
: on P attack the C and kicks off Br.
now u have PPh3 cyclohexane but its (+)
N butyl lithium is a strong base and removes the H on the C thats bonded to the PPh3
the e- go to the carbon and give it a (-) this is called a YLIDE!! positive P, negative C
then the negative goes to the C-P bond to neutralise the P and the C and forms a double bond PHOSPHORANE!!
YLIDE AND PHOSPHORANE AREEE
basically resonance structures of themselves
PPh3 (+) and C (-) is a
ylide
what can a ylide do
the (-) on the C can attack carbonyl C’s.
the (+) PPh3 can accept electrons from the carbonyls double bond
this forms a small ring of C C O P called oxaphosphetane
draw arrow Past P and an arrow past the HR to collapse the ring
this gives an alkene + phsophine oxide
describe phosphine oxide
R R R P = O
what forms an alkene
R-Br + PPh3 + aldehyde
one R from each (the thing the PPh3 attacked and the R from the aldehyde)
either cis or transsss
what is more likely to give a z alkene // same side
an unstable ylide
what is more liekly to form an E ylide ,, diff side
a stable ylide
stable ylide
E
unstable ylide
Z
no time to rotate and give an E (more stable due to steric repulsion) due to being so unstable and being so reactive.
describe an unstable ylide
R - C - PPh3
where R is an alkyl
C is (-)
PPh3 is (+)
its unstable bc the R is an alkyl which means it donates e- density towards the already - C
describe a stable ylide
R C PPh3
where R is a carbonyl,, so the (-) can be resonated onto the carbonyls O,, forming an O- and it being more stable.
where C is (-)
and where PPh3 is (+)
unstable ylide what does it give and why
gives a z alkene
gives a SYN OXAPHOSPHETANE (box made up of C C O PPh3 )
syn bc both H’s are wedged // dashed
this is bc we want the R group as far away from the PPh3 as possible,, to prevent steric hinderance and instability.
are aldehydes and ketones more electrophilic than esters
yessss
bc they only have inductive effect making the C more (-)
and inductive effect is weaker than resonance.
stable ylides,, what they give and why
stable ylides give E isomers (think that thry have more time to rotate and give the preferred isomer)
they also give an ANTI OXAPHOSPHETANE,, where one H is dashed and the other one is wedged.
this is bc we dont rlly care about the steric hinderance between the R (carbonyl) and the PPh3,, we care more about the 2 electronegative groups being close together (the o and the carbonyl)
so we line the carbonyl up with the R group.
describe a sulfonium salt then describe what happens when u react it with a base
S (+) Me Me Me
base: removes a H,, u get S staying (+) and a CH2 being (-)
SULFONIUM YLIDE BC C IS - AND S IS +
describe a sulfoxide and what happens when u react it with a base
ketone but with an S instead of a C
u remove an alpha H and it gives u a (-) on that carbon
describe a sulfone and how it reacts with a base
R S = O = O - R
with a base u remove a H near the sulfur,, which gives u a (-)
julia olesenation
when u have the r s =o =o - r thing and u use a base to remove a H and give u a (-)
this attacks a C on a different carbonyl and forms an O-
the lone pair on the O- then attacks another carbonyl C and forms another O- (u remove the R aswell tho so u get an ester)
B removes a H by the S and a double bond is formed and the ester is removed
treating it with Na removes the sulfur and its o’s. giving u a double bond and a (-) on one end of the doiuble bond
u work it up with H3O+ to give an alkeneee (an E alkene in this case) E alkene is the major product..
julia mech simplified
u use the r s=o =o - r and a base to attack a carbonyl.
then use that carbonyl to attackabother one and form an ester
u then use a base to form a double bond and remove that ester.
u then use Na to remove the sulfur bit of it (gives off a smally gas) u get a double bond with a (-)
then u work it up with H3O+ to give an alkene
