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Organic and biological > Louis U2 > Flashcards

Louis U2 Flashcards

1
Q

homolytic bond cleavage / homolysis

A

when a bond breaks and the atoms get 1 bonding electron each - radicals formed

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2
Q

heterolytic bond cleavage / heterolysis

A

when a bond breaks and 1 atom gets both bonding electrons - ions formed

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3
Q

what is BDE

A

the energy required for homolytic cleavage

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4
Q

what does a high BDE show

A

a strong bond, poorly stabilised radicals formed

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5
Q

what does a low BDE show

A

a weak bond, highly stabilised radicals formed

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6
Q

If a reaction has a neg delta H it is..

A

exothermic (causes surrounding temp to increase)

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7
Q

if a reaction has a pos delta H it is..

A

endothermic (causes surrounding temp to decrease)

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8
Q

what is entropy (S)

A

measure of disorder in the system

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9
Q

equation for Gibbs free energy

A

(dH-T) X dS

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10
Q

negative dG

A

corresponds to exergonic process

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11
Q

pos dG

A

corresponds to endergonic process

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12
Q

what does the reaction order for a reagent tell us

A

tells us how many molecules of that reagent participate in the rate determining step

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13
Q

Rate of first order reaction

A

Rate = Kobs[A]1

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14
Q

Rate of second order reaction

A

Rate = Kobs[A]1[B]1

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15
Q

Rate of third order reaction

A

Rate = Kobs[A]1[B]2

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16
Q

rate constant units of 1st order reaction

A

s-1

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17
Q

rate constant units of 2nd order reaction

A

l mol-1s-1

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18
Q

rate constant units of 3rd order reaction

A

l2 mol-2s-1

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19
Q

as activation energy increases/decreases, k increases/decreases, rate increases/decreases

A

as Ea increases, k decreases, rate decreases

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20
Q

as temp increases/decreases, k increases/decreases, rate increases/decreases

A

as temp increases, k increases, rate increases

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21
Q

what is an intermediate

A

a molecule/ion that appears at a localised energy min

22
Q

what is a transition state

A

represents an energy maximum - contains bonds that are partially formed and/or partially broken

23
Q

what are the 4 main ways electrons flow in ionic reactions

A

nucleophillic attack, loss of a leaving group, proton transfers, sigma bond migration

24
Q

when does loss of a leaving group occur

A

when a bond breaks and 1 atom from the bond retains both electrons - the electrons move to the more electronegative atom

25
Q

describe the SN1 substitution mechanism

A

the leaving group goes first, forming a carbocation intermediate that is attacked by a nucleophile in a second step

26
Q

describe the SN2 substitution mechanism

A

Nucleophile attacks at the same time as leaving group goes

27
Q

a good leaving group is..

A

the conjugate base of a strong acid (acids with low pKa

28
Q

describe the changes of hybridisation at Carbon during SN2

A

changes from sp3 to sp2 back to sp3

29
Q

What must the nucleophile be for SN2 reaction

A

small/less bulky, leads to a less congested trans state and a faster reaction

30
Q

what is nucleophilicity affected by

A

solvent choice

31
Q

what is a polar protic solvent

A

at least 1 H atom connected directly to an electronegative atom

32
Q

what is a polar aprotic solvent

A

no H atoms connected directly to an electronegative atom

33
Q

How do polar protic solvents work

A

cations and anions are both solvated, reducing the energy of the nucleophile HOMO (decreased nucleophilicity)

34
Q

How do polar aprotic solvents work

A

only cations are solvated, maintaining the energy and hence nucleophilicity of the anion

35
Q

rate of SN1 substitution dependent only on what

A

electrophile conc

36
Q

Rate law of SN1 sub

A

Rate = Kobs[substrate]1

37
Q

racemisation

A

when a compound undergoes a reaction and the transformation produces an equal mixture of both possible enantiomers

38
Q

what solvent is typically used for an SN1 reaction

A

polar protic

39
Q

give 3 examples of polar protic solvents for SN1 reactions

A

methanol, water, acetic acid, sulfuric acid and hydrochloric acid

40
Q

best substrate for SN2 reaction

A

methyl/primary halides

41
Q

best substrate for SN1 reaction

A

tertiary halides

42
Q

describe the E2 elimination mechanism

A

Leaving group leaves and deprotonation occur at the same time (1 step)

43
Q

describe the E1 elimination mechanism

A

Leaving group leaves first, then the deprotonation by a base (2 step)

44
Q

describe the E1cb elimination mechanism

A

deprotonation by a base, then the leaving group goes (2 step)

45
Q

what is Zaitsev’s rule (E1 elim reaction)

A

E1 elimination always favours the more substituted and more stable alkene product

46
Q

why are more substituted alkenes more stable

A

due to overlap between filled sigma orbitals and the empty pi star orbital of the alkene

47
Q

what type of base favours an E1 reaction

A

Bronsted base favours E1 - weak bases

48
Q

type of solvent for an E1 reaction

A

polar protic

49
Q

type of solvent for an E2 reaction

A

polar aprotic

50
Q

an increase in reaction temp favours which reactions

A

eliminations (E1 and E2)

Organic and biological (4 decks)

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