ch 7 o chem Flashcards
What makes a stable alkene
e (trans) 0 h = o h more substituted (less H)
dehydroghalogenation of alkyl halides
you have an alkane and then a base and Hx comes and takes off the alkyl halide and makes it =
dehydrogenation of alcohols
alkali + h+, heat, HOH, it takes of the OH and makes a alkene
what are the base+solvents for dehydrohalogenation?
what are the bases and how are they made
KOH + EtOH
t-butOK+t-butOH
EtONa+ EtOH
bases are alkoxides , they are alcohols but then u put them
rate for E2
how is the LG and H placed in E2
r8= k[base][alkane]
one is in front one is in back on Newman but they are one up and one down
what are regioisomers
when the E2 can happen from multiple different places with H then it gives constitutional isomers, regioisomers
what are sterioisomers (E2)
when th E2 can give a cis or a trans (wedge and dash for things and then u take out the H so now its one is cis and one is trans)
in a cyclohexane thing how do u prepare for E2
make sure LG is axial, chair might beed to be flipped
regio and seterioisomers form through the law of zeitozkjhf if…
its a small base being used
ETONa or KOH
Hofmann rule
if u use bulky base (t-butOH) for E then it will only use one spot mainly because its so fat
which favours e more vs sn
the more substituted the more e2
e or s 1 or 2 ?
3º + weak base
3º + strong base
3º + weak base
sn1
3º + strong base
E1
how to dehydrate the different alchohols
1º hardest 180º and conc h2so4 2º 165-170º and h3po4 (rearranges) 3º 85º and h2so4
acidity of the h related to the alkene position
Terminal alkene = not very acidic
middle alkene = medium acidity
no alkene = more acidic
to make a terminal alkene you need how many mols of base
1 more than the amount of h your abstracting+you need a step at the end to give a H so its not + charge
dehydration vs hydrogenation
dehydration=making double bond
hydrogenation = taking out double bond
catalysts for hydrogenation
pt pd Ni (hetero, doesn’t mix with solvent(different phase))
Wilkinson’s catalyst = homo (mixes with solvent)
syn vs anti addition
SYN: The things are added cis
ANTI : the things are added grandly
is catalytic hydrogenation sin or trans
Adding H gas is added syn
for hydrogenation of alkynes how Manny hs do you use
2H2
what is semi hydrogenation of alkyne
when it goes from alkyne to alkene
use H2 added syn
how to make alkyne to alkene trans
use
Na, NH3 (l) -78ºc
Ni, NH3 (l) -78ºc
how to make alcohols from alkenes? (oxymercuration, demurcuration)
step one:
Hg(OAC)2 and THF-H2O
step 2:
NaBH4 and OH
hallogen addition
they will be added trans even if it doesn’t seem like it can be. it does a weird thing where it takes one of the halogens that bonds with both c breaking the=
then the other halogen attacks from the back and now they are attatched trans
syn dihydroxylation reagents
1)OsO4
2)NaHSO3/H2O
it breaks the = and now there are oh added syn (cis)
oxidative cleavage of alkenes
use hot KNO4 OH-, H2o heat or O3, CH2Cl2,-78º
cut = in two look at groups attached to the c on each end of =
if its:
2 R groups: just add o the end with =
1R I H: add o to end with = and replace H with OH (the H is added in a next step with H3O)
2H groups: it will end with O=C=O + h2o
oxidative cleavage = of alkynes
reagents: 1) O3, 2) HOAc or 1)KMnO4, OH- 2)H3O+
