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organic sem 2 > lecture 1 + 2 > Flashcards

lecture 1 + 2 Flashcards

1
Q

what hybridisation is seen in alkenes

A

sp2 hybridisation

1 sigma bond
1 pi bond

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2
Q

is the pi bond in alkenes the nucleophile or electrophile

A

nucleophile

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3
Q

if the the pi bond is the nuc,, what orbital are the e- in

A

the HOMO

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4
Q

what is Br2 in reactions

A

electrophile

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5
Q

where are e- accepted into in Br2 when it reacts

A

into the LUMO
sigma ** star

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6
Q

what happens to ethene when it reacts with Br2

A

1 Br attaches and forms a carbo cation intermediate

this is unstable as its primary
the lone pairs on Br donate e- density and it forms the BROMONIUM ION + Br-

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7
Q

product of ethene and Br2

A

BROMONIUM ION +
important intermediate

and Br-

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8
Q

describe the bromonium ion

A

2 carbons at the bottom linking to a Br at the top

the Br has a (+) charge

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9
Q

what can the BROMONIUM ion react with

A

can react with the Br-

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10
Q

how does the BROMONIUM ION react with Br-

A

the Br- attacks one of the bottom carbons

the e- in the C-Br breaks and goes into the Br+

forms 1-2 dibromoethane (dibromo derivative)

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11
Q

how else can we draw the reaction of ethene and Br2

A

• = attacks the Br-Br
• e- go to the end Br
• First Br’s lone pair attacks the = other end

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12
Q

what is hyperconjugation and how does it stabilise an alkene

A

when e- in a CH sigma bond have a side on interaction with the empty C=C pi star orbital.

this leads to the 2e- in the CH sigma to be spread over the molecule + delocalised, increasing its stability

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13
Q

why can double bonds be nucleophiles

A

they’re electron rich

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14
Q

a more substituted double bond is

A

more stable

also more reactive to electrophilic addition

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15
Q

why are more substituted double and triple bonds more reactive for electrophilic addition reactions

A

alkyl groups have an e- donating effect making the double / triple bond more e- rich and therefore more nucleophilic

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16
Q

why do F substituted double and triple bonds lose reactivity to electrophilic addition reactions

A

bc the F attracts some e-
double / triple bond is less nucleophilic

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17
Q

what reactions are used to make alkenes

A

elimination reactions
waterfalls

halogenoalkanes are used

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18
Q

in electrophilic additions with halogenoalkanes, what C does the H and X bond to

A

H bonds to the C that’s bonded to the lowest amount of carbons

X bonds to the C that’s bonded to the highest amount of carbons

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19
Q

what is the meaning of a regioselective reaction

A

there is a selective formation of one of the isomers

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20
Q

markovnikoffs product

A

H bonds to the C with little c

X bonds to the C with big c

makes a more stable CC+

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21
Q

what is the bonding interaction between an alkene and a HX

A

the pi bonding HOMO (ALKENE)
the sigma star LUMO (HX)

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22
Q

in a gibbs energy of activation graph, where is the more stable CC+ intermediate

A

at a lower G value then the primary CC+

more stable = lower G energy value

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23
Q

hydride and alkyl shift

A

when the H or CH3 move with 2 e- in order to form a more stable CC+

arrow from the CH bond to the CC+

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24
Q

an alkene and Br2 form

A

1,2-dibromoalkanes

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25
Q

what does 1,2-dibromo mean

A

that the Bromines are on adjacent carbons

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26
Q

antiaddition of Bromine to an alkene

A

makes an E isomer

first Br makes a ring
second Br ring opens (SN2) at any C opposite the first Br (LG) on the BROMONIUM ION +

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27
Q

another name for 1,2-dibromoalkanes

A

vicinal dibromides

the bromides are in the same vicinity (adjacent Cs)

28
Q

syn addition of Br2 to an alkene

A

= is the nuc
Br2 is the electrophile
forms the bromonium ion
Br- attacks on the same C that the Br (LG) will remain attached to

29
Q

what mix occurs when making the bromonium ion

A

racemic mix

the Br2 can attack both sides of the double bond

30
Q

a racemic mix of bromonium ions leads to a racemic mix of

A

the dibromide product
(the alkene)

31
Q

what occurs in a stereospecific reaction

A

different stereoisomer reactants produce different stereoisomers of the product

32
Q

the bromonium ions from a Z and E are

A

diastereoisomers

33
Q

1 bromonium ion from a Z alkene gives

A

2 possible products
SS or RR

enantiomers

34
Q

one bromonium ion from a E alkene gives

A

2 possible products
RS + SR (meso compounds)

bc the Br- attacking the Cs on the bromonium ion gives the same products

ACHIRAL - line of symmetry

35
Q

the 2 products from alkene Z and 2 from alkene E are

A

diastereoisomers
NOT ALL THE CHIRAL CENTRES CHANGE

Z = RR + SS
E = RS + SR

36
Q

Z isomer and Br2 addition

A

alkene
bromonium ion
racemate

37
Q

E isomer and Br2 addition

A

alkene
bromonium ion
meso compounds (achiral) SR RS

38
Q

E and Z isomer and Br2 addition products

A

diastereomers

39
Q

Br2 addition is

A

stereospecific
- product depends on reactant

40
Q

alkene with Br2 and MeOH / H2O
SN2

A

alkene + Br -> bromonium ion
MeOH / H2O ring open
-H+ to give an XXX / alcohol

41
Q

alkene + Br2 + MeOH/H2O
SN1

A

alkene + Br -> bromonium ion
ring open to form a CC+ (most stable)
MeOH / H2O attacks the CC+
-H+ to get XXX / alcohol products

42
Q

why does the alkene + Br2 + MeOH only have 1 product when the alkene is asymmetric

A

the MeOH attacks the most stable CC+
tertiary Carbon

43
Q

ANTI ADDITION

A

when the Br electrophile and Br nucleophile attack at different sides

2nd Br must attack the C that’s opposite the Br (180* attack)

44
Q

cyclohexene + Br2

A

benzene attacks Br
bromonium ion forms (both dashed)
Br attacks the C at 180 to Br+
one Br is dashed, one is wedged (ANTI)
(enantiomers formed, racemic mix formed)

45
Q

bromonium ion and a nuc attack description

A

if the bromonium ion is symmetrical, the NUC can attack any C on the Bromonium ion

if asymmetric, we need to look at E isomers or the most stable CC+

46
Q

electrophilic addition of HX to cyclohexene

A

H is attacked by nuc (double bond)
no bromonium / ring system is made

CC+ is made
Br- then attacks this CC+

47
Q

asymmetric alkene and HX electrophilic addition (arrow from double bond to HX)

A

follow markovnikoffs rule

H attached to C with little Cs
X attached to C with most Cs

48
Q

phenyl group and an SH group is called a

A

thiol

49
Q

how are thiols made

A

benzene
H2S (nuc)
H2SO4 (electrophile / catalyst / H+ source)

50
Q

what is an epoxide /oxirane

A

a 3 member ring with O as one of the members

51
Q

how do we form an epoxide from an alkene

A

alkene + oxidation = epoxide

[O] reagent

52
Q

what is a peroxy carboxylic acid

A

a carboxylic acid with an additional ‘o’ between the o and c

it prevents resonance structures from forming when the H is removed, allowing the original O to be + and electrophilic (nucs attack it) 21.3 book

53
Q

what is formed when a peroxy carboxylic acid is attacked by a nuc

A

NUC OH and

R-C=O
|
O- stable carboxylate (good LG)

54
Q

alkene + peroxy carboxylic acid reaction

A

epoxidation - electrophilic addition
peroxy carboxylic acid donates an O to the C=C forming an epoxide + carboxylic acid

55
Q

why is the peroxy carboxylic acid OH ‘O’ partially positive

A

the RCO2 withdraws electrons via induction / inductive effects

making the extra O more -

56
Q

peroxy carboxylic acid reaction

A

O from OH = + and is attacked
O-O e- break and form a double bond between O and C

old O and C double bond breaks to attack H from OH
arrow from H to the = of nuc

57
Q

a trans alkene + peroxy carboxylic acid gives a

A

trans epoxide
one R is dashed one R is wedged

58
Q

a cis alkene and peroxy carboxylic acid makes a

A

cis epoxide
both Rs from the alkene are dashed / wedged

59
Q

meta chloro perbenzoic acid

A

mCPBA
benzene with Cl meta and
peroxy carboxylic acid attached

60
Q

benzene and mCPBA gives

A

mcBA
cyclohexane epoxide

concerted process - all at the same time - no cationic / anionic intermediates

61
Q

when mCPBA react with an alkene the product is

A

EPOXIDE (cis or trans depending on the alkene)

mCBA

62
Q

diff between mCPBA and mCBA

A

mCPBA = meta chloro perbenzoic acid (3 Os in total) (peroxy carboxylic acid)

mCBA = product = meta chloro benzoic acid ( 2 Os only)( carboxylic acid with a benzene with Cl on meta position)

63
Q

apart from epoxilation using an alkene and mCPBA, how else can an epoxide be formed

A

alkene + DMDO -> acetone + EPOXIDE

64
Q

what is dmdo

A

di methyl dioxirane

camping chair with two Os on the top

65
Q
A
66
Q
A

organic sem 2 (14 decks)

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