lecture 4 Flashcards
what does it mean when a compound is called a diene
it has 2 double bonds
what is an ordinary diene
a compound with 2 double bonds
what is a conjugated diene
a diene where the 2 double bonds are conjugated
aka single, double, single, double
whats a cisoid // s-cis diene
when the conjugated double bonds are on the same side.
table with 2 legs on each saide on the same side
what is a transoid // s-trans
when the conjugated double bonds are on opposite sides of the single bond
which are more stable: cisoid or transoid and why
transoid bc there is less steric hinderance and repulsion between the 2 double bonds as they are more spread out
what is a cumulated diene
when the 2 double bonds are right next to eachother
theyre allenes
c=c=c
another word for cumulated diene
allene
can allenes be chiral
yes
if a carbon is bonded to 2 different groups (2 different substituents)
the double bonds in an allene are described as
consecutive, not conjugated
theyre one after the other
c=c=c
are allenes flat
no
the 2 double bonds are at right angles to eachother
describe a chiral allene
the carbon is bonded to 2 different groups
what is an alkyne
triple carbon bond
what geometric shape is a alkyne
its 180*
linear
what hydridisation is an alkyne
sp hybridised
alkynes can react with H+ Br- ,, decribe this reaction when HBr is not in excess
triple bond attacks the H+
the most stable CC+ is formed
the Br- attacks this CC+ and it forms an alkene with a Br
alkynes can react with HBr,, describe this reaction when HBr is in excess
alkyne attacks H+
forms CC+
Br- attacks the CC+
forms an alkene
alkene = attacks H+
forms CC+
Br- attacks CC+
alkane is formed
what is needed to hydrate an alkyne
H+
H20
describe alkyne hydration using H+ and H2O🌷
the alkyne triple bond attacks the H+ and forms a CC+
the H2O attacks this CC+
a H is then removed from the H2O to neutralise it
this forms an ENOL (OH attached to double bond) the e- from O-H form a couble bond between the C and O.
the double bond attacks a H+.
which gives a ketone.
describe the reaction between an enol and a ketone🌷
its a reversible reaction
between an enol and a ketone
the ketone is preferred
Hg 2+ is used as a catalyst
TAUTOMERISATION
difference between hydrogenation and hydration
hydration: h2o is added to a molecule
hydrogenation: H is added to a molecule
alkyne hydrogenation reaction needsss
alkyne
H2
lindar catalyst
lindar catalyst examples
Pd
CaCO3
PbO
lindar catalysts are used on
alkynes
alkenes
hydrogenation of an alkyne to form a Z alkene description
alkyne + H2 + LC (Pd)
alkyne gets closer to the Hs on the metal catalyst
1 e- movement opening the triple bond and e- from the H towards the alkyne
forms a Z alkene as both Hs attach to the same side
Z alkene and H2 and Pd (LC) reaction description
alkene gets closer to the Hs absorbed onto the metal catalyst
Hs attach on the same side forming an alkane
hydrogenation of an alkyne to form an E alkene
alkyne + Na + NH3
forms an E alkene and 2NaNH2
1st step of alkyne hydrogenation to form an e alkene
the NH3 and Na react (-20* and liquid) to form Na+ and e-(NH3)n
what is the purpose of reacting NH3 and Na
to form
e-(NH3)n
solvated e-
deep blue colour
2nd step of hydrogenation of an alkyne to form a e alkene
the soluvated e-(NH3) attack the C causing the triple bond to open towards both Cs
these are all 1 e- movements
this forms an e alkene with a radical on 1 C and a - charge on the other (radical anion)
the negative charge then attacks NH3 for its H
3rd step for hydrogenating a alkyne to form an e alkene
the alkene now has a neutral carbon and another carbon with a radical (VINYL RADICAL)
this is reacted with NaNH2 and soluvated e- in order to gain a negative charge
4th step for hydrogenating an alkyne to form an e alkene
the anion
alkene with one of the carbons having a - charge attacks NH3 in order to get one of its Hs and become a E alkene
