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organic sem 2 > lecture 4 > Flashcards

lecture 4 Flashcards

1
Q

what does it mean when a compound is called a diene

A

it has 2 double bonds

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2
Q

what is an ordinary diene

A

a compound with 2 double bonds

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3
Q

what is a conjugated diene

A

a diene where the 2 double bonds are conjugated

aka single, double, single, double

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4
Q

whats a cisoid // s-cis diene

A

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

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5
Q

what is a transoid // s-trans

A

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

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6
Q

which are more stable: cisoid or transoid and why

A

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

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7
Q

what is a cumulated diene

A

when the 2 double bonds are right next to eachother

theyre allenes

c=c=c

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8
Q

another word for cumulated diene

A

allene

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9
Q

can allenes be chiral

A

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

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10
Q

the double bonds in an allene are described as

A

consecutive, not conjugated

theyre one after the other

c=c=c

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11
Q

are allenes flat

A

no

the 2 double bonds are at right angles to eachother

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12
Q

describe a chiral allene

A

the carbon is bonded to 2 different groups

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13
Q

what is an alkyne

A

triple carbon bond

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14
Q

what geometric shape is a alkyne

A

its 180*
linear

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15
Q

what hydridisation is an alkyne

A

sp hybridised

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16
Q

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

A

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

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

17
Q

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

A

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

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

18
Q

what is needed to hydrate an alkyne

A

H+
H20

19
Q

describe alkyne hydration using H+ and H2O

A

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.

20
Q

describe the reaction between an enol and a ketone

A

its a reversible reaction
between an enol and a ketone

the ketone is preferred

Hg 2+ is used as a catalyst

TAUTOMERISATION

21
Q

difference between hydrogenation and hydration

A

hydration: h2o is added to a molecule

hydrogenation: H is added to a molecule

22
Q

alkyne hydrogenation reaction needsss

A

alkyne
H2
lindar catalyst

23
Q

lindar catalyst examples

A

Pd
CaCO3
PbO

24
Q

lindar catalysts are used on

A

alkynes
alkenes

25
Q

hydrogenation of an alkyne to form a Z alkene description

A

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

26
Q

Z alkene and H2 and Pd (LC) reaction description

A

alkene gets closer to the Hs absorbed onto the metal catalyst

Hs attach on the same side forming an alkane

27
Q

hydrogenation of an alkyne to form an E alkene

A

alkyne + Na + NH3

forms an E alkene and 2NaNH2

28
Q

1st step of alkyne hydrogenation to form an e alkene

A

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

29
Q

what is the purpose of reacting NH3 and Na

A

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

30
Q

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

A

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

31
Q

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

A

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

32
Q

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

A

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

33
Q
A

organic sem 2 (14 decks)

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