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organic sem 2 > lecture 1 + 2 > Flashcards

lecture 1 + 2 Flashcards

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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
what does 1,2-dibromo mean
that the Bromines are on adjacent carbons
26
antiaddition of Bromine to an alkene
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 +
27
another name for 1,2-dibromoalkanes
vicinal dibromides the bromides are in the same vicinity (adjacent Cs)
28
syn addition of Br2 to an alkene
= 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
what mix occurs when making the bromonium ion
racemic mix the Br2 can attack both sides of the double bond
30
a racemic mix of bromonium ions leads to a racemic mix of
the dibromide product (the alkene)
31
what occurs in a stereospecific reaction🌷
different stereoisomer reactants produce different stereoisomers of the product
32
the bromonium ions from a Z and E are
diastereoisomers
33
1 bromonium ion from a Z alkene gives🌷
2 possible products SS or RR enantiomers
34
one bromonium ion from a E alkene gives🌷
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
the 2 products from alkene Z and 2 from alkene E are🌷
diastereoisomers NOT ALL THE CHIRAL CENTRES CHANGE Z = RR + SS E = RS + SR
36
Z isomer and Br2 addition
alkene bromonium ion racemate
37
E isomer and Br2 addition
alkene bromonium ion meso compounds (achiral) SR RS
38
E and Z isomer and Br2 addition products
diastereomers
39
Br2 addition is
stereospecific - product depends on reactant
40
alkene with Br2 and MeOH / H2O SN2
alkene + Br -> bromonium ion MeOH / H2O ring open -H+ to give an XXX / alcohol
41
alkene + Br2 + MeOH/H2O SN1
alkene + Br -> bromonium ion ring open to form a CC+ (most stable) MeOH / H2O attacks the CC+ -H+ to get XXX / alcohol products
42
why does the alkene + Br2 + MeOH only have 1 product when the alkene is asymmetric🌷
the MeOH attacks the most stable CC+ tertiary Carbon
43
ANTI ADDITION
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
cyclohexene + Br2🌷
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
bromonium ion and a nuc attack description🌷
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
electrophilic addition of HX to cyclohexene🌷
H is attacked by nuc (double bond) no bromonium / ring system is made CC+ is made Br- then attacks this CC+
47
asymmetric alkene and HX electrophilic addition (arrow from double bond to HX)
follow markovnikoffs rule H attached to C with little Cs X attached to C with most Cs
48
phenyl group and an SH group is called a
thiol
49
how are thiols made🌷
benzene H2S (nuc) H2SO4 (electrophile / catalyst / H+ source)
50
what is an epoxide /oxirane🌷
a 3 member ring with O as one of the members
51
how do we form an epoxide from an alkene🌷
alkene + oxidation = epoxide [O] reagent
52
what is a peroxy carboxylic acid🌷
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
what is formed when a peroxy carboxylic acid is attacked by a nuc🌷
NUC OH and R-C=O | O- stable carboxylate (good LG)
54
alkene + peroxy carboxylic acid reaction🌷
epoxidation - electrophilic addition peroxy carboxylic acid donates an O to the C=C forming an epoxide + carboxylic acid
55
why is the peroxy carboxylic acid OH ‘O’ partially positive
the RCO2 withdraws electrons via induction / inductive effects making the extra O more -
56
peroxy carboxylic acid reaction🌷
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
a trans alkene + peroxy carboxylic acid gives a🌷
trans epoxide one R is dashed one R is wedged
58
a cis alkene and peroxy carboxylic acid makes a🌷
cis epoxide both Rs from the alkene are dashed / wedged
59
meta chloro perbenzoic acid🌷
mCPBA benzene with Cl meta and peroxy carboxylic acid attached
60
benzene and mCPBA gives🌷
mcBA cyclohexane epoxide concerted process - all at the same time - no cationic / anionic intermediates
61
when mCPBA react with an alkene the product is🌷
EPOXIDE (cis or trans depending on the alkene) mCBA
62
🌷diff between mCPBA and mCBA
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
apart from epoxilation using an alkene and mCPBA, how else can an epoxide be formed🌷
alkene + DMDO -> acetone + EPOXIDE
64
what is dmdo
di methyl dioxirane camping chair with two Os on the top

organic sem 2 (15 decks)

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