lecture 4

Question 1

what does it mean when a compound is called a diene

Answer 1

it has 2 double bonds

Question 2

what is an ordinary diene

Answer 2

a compound with 2 double bonds

Question 3

what is a conjugated diene

Answer 3

a diene where the 2 double bonds are conjugated

aka single, double, single, double

Question 4

whats a cisoid // s-cis diene

Answer 4

when the conjugated double bonds are on the same side.
table with 2 legs on each saide on the same side

Question 5

what is a transoid // s-trans

Answer 5

when the conjugated double bonds are on opposite sides of the single bond

Question 6

which are more stable: cisoid or transoid and why

Answer 6

transoid bc there is less steric hinderance and repulsion between the 2 double bonds as they are more spread out

Question 7

what is a cumulated diene

Answer 7

when the 2 double bonds are right next to eachother

theyre allenes

c=c=c

Question 8

another word for cumulated diene

Answer 8

allene

Question 9

can allenes be chiral

Answer 9

yes
if a carbon is bonded to 2 different groups (2 different substituents)

Question 10

the double bonds in an allene are described as

Answer 10

consecutive, not conjugated

theyre one after the other

c=c=c

Question 11

are allenes flat

Answer 11

no

the 2 double bonds are at right angles to eachother

Question 12

describe a chiral allene

Answer 12

the carbon is bonded to 2 different groups

Question 13

what is an alkyne

Answer 13

triple carbon bond

Question 14

what geometric shape is a alkyne

Answer 14

its 180*
linear

Question 15

what hydridisation is an alkyne

Answer 15

sp hybridised

Question 16

alkynes can react with H+ Br- ,, decribe this reaction when HBr is not in excess

Answer 16

triple bond attacks the H+
the most stable CC+ is formed

the Br- attacks this CC+ and it forms an alkene with a Br

Question 17

alkynes can react with HBr,, describe this reaction when HBr is in excess

Answer 17

alkyne attacks H+
forms CC+
Br- attacks the CC+
forms an alkene

alkene = attacks H+
forms CC+
Br- attacks CC+
alkane is formed

Question 18

what is needed to hydrate an alkyne

Answer 18

H+
H20

Question 19

describe alkyne hydration using H+ and H2O🌷

Answer 19

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.

Question 20

describe the reaction between an enol and a ketone🌷

Answer 20

its a reversible reaction
between an enol and a ketone

the ketone is preferred

Hg 2+ is used as a catalyst

TAUTOMERISATION

Question 21

difference between hydrogenation and hydration

Answer 21

hydration: h2o is added to a molecule

hydrogenation: H is added to a molecule

Question 22

alkyne hydrogenation reaction needsss

Answer 22

alkyne
H2
lindar catalyst

Question 23

lindar catalyst examples

Answer 23

Pd
CaCO3
PbO

Question 24

lindar catalysts are used on

Answer 24

alkynes
alkenes

Question 25

hydrogenation of an alkyne to form a Z alkene description

Answer 25

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

Question 26

Z alkene and H2 and Pd (LC) reaction description

Answer 26

alkene gets closer to the Hs absorbed onto the metal catalyst Hs attach on the same side forming an alkane

Question 27

hydrogenation of an alkyne to form an E alkene

Answer 27

alkyne + Na + NH3 forms an E alkene and 2NaNH2

Question 28

1st step of alkyne hydrogenation to form an e alkene

Answer 28

the NH3 and Na react (-20* and liquid) to form Na+ and e-(NH3)n

Question 29

what is the purpose of reacting NH3 and Na

Answer 29

to form e-(NH3)n solvated e- deep blue colour

Question 30

2nd step of hydrogenation of an alkyne to form a e alkene

Answer 30

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

Question 31

3rd step for hydrogenating a alkyne to form an e alkene

Answer 31

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

Question 32

4th step for hydrogenating an alkyne to form an e alkene

Answer 32

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