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drug structure > Influence of electronic and structural effects on acidity > Flashcards

Influence of electronic and structural effects on acidity Flashcards

1
Q

what happens when there’s an increase in pKa (increase in electronegativity)?

A

increase in acidity
more stabilization of conjugate base

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2
Q

what are the inductive effects of electrons being withdraw in an equilibirum?

A

stabilizing of the molecule

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3
Q

what is the inductive effect of electrons being donated in an equilibrium?

A

destabilizing of the molecule

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4
Q

what do electron withdrawing groups do to the acidity?

A

increase it

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5
Q

what does increasing the halogen atom do to the acidity?

A

increase in acidity
one chlorine increases acidity by a factor of 100
increasing the inductive effect

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6
Q

what is trichloroacetic acid?

A

strong acid

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7
Q

what are the electron donating groups?

A

opposite effect
increases electron density
destabilizing base
therefore forming weaker acid

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8
Q

what are the most common electron donating group?

A

alkyl groups

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9
Q

how does hybridization effect acidity?

A

the hybridization of carbon atom attached to acidic H effects acidity
the more S orbital an atom has the closer it is to the nucleus so more electronegative, and more acidic and more stable

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10
Q

which are more electronegative: sp, sp2, sp3?

A

sp most
sp2
sp3 lowest

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11
Q

how is delocalization of charge in base a stabilising factor?

A

through resonance

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12
Q

effect of halogen group in a benzene?

A

the closer it is to the carboxyl group the lower the pKa

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13
Q

effect of nitrophenols in benzene with ortho or para names?

A

further delocalization of acidic charge
increasing acidity

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14
Q

is m-nitrophenol less acidic for having a higher pKa than o-nitrophenol and p-nitrophenol?

A

no because inductive effect helps stabilize the anion

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15
Q

effect of more nitroxide groups on a phenol?

A

if there are more nitroxide groups on a phenol the more acidic it is

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16
Q

what is a base?

A

will accept a proton by donating a pair of electrons

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17
Q

how do we measure the strength of a base?

A

using the pKa of its conjugate base

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18
Q

what is the difference between a strong base and a weak base?

A

strong base has a small Ka and large pKa
weak base has a large Ka and small pKa

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19
Q

what is bascicity?

A

‘ability of a compound to use its non bonding electrons to bond with a proton’

20
Q

what makes an acid stronger?

A

increasing stability of conjugate base
favouring loss of proton from acid

21
Q

what is a more stable base?

A

a weaker base

22
Q

what is more ready to donate electrons to a proton, anionic base or neutral base?

A

anionic base

23
Q

what happens to basicity as atom becomes more electronegative in a compound?

A

basicity decreases as atom becomes more electronegative

24
Q

what makes a base stronger?

A

increasing stability of conjugate acid

25
Q

what does H-bonding do to the positive charge on nitrogen compounds?

A

H-bonding stabilizes cations

26
Q

what does increasing acidity do?

A

increases stability of conjugate base

27
Q

what stabilizes the conjugate base?

A

discourages protonation making it a weaker base

28
Q

what does more stability mean about the base?

A

the more stable a base the weaker the base

29
Q

what does delocalized elctrons mean about the basicity

A

if electrons are delocalized the less basic the compound is

30
Q

what is the inductive effect of methyl addition to nitrogen?

A

increases basic strength

31
Q

why does addition of second methyl group have a lower effect and a third methyl group decreases the basicity?

A

H-bonding stabilizes the positive charge on nitrogen
increase in alkyl groups decreases the effect

32
Q

what is the effect of electron withdrawing groups?

A

decrease electron density which destabilizes conjugate acid making it less likely to pick up a proton making the base weaker

33
Q

relationship between acidity and p character?

A

the acidity of the of C-H decreases as the p character increases

34
Q

why is it harder to protonate in sp orbital than sp3?

A

if lone pair in sp orbital than electrons held closer to nucleus so harder to protonate than if in sp3 orbital so not basic

35
Q

what happens in the delocalization of charge of conjugate base of anions?

A

stabilizes anion
increase in ionization of anion

36
Q

what happens when delocalization of base happens?

A

stabilizes base reducing basicity

37
Q

when does resonance stabilization occur with an amide?

A

with O-protonated amide (where H has attached to oxygen)
not with N-protonated amide (where H has attached to nitrogen)

38
Q

how does resonance stabilization occur in O -protonates amides?

A

lone pair on nitrogen is able to overlap into p system

39
Q

how does resonance stabilization occur in amidines?

A

the nitrogen replacing oxygen becomes protonated allowing stabilization of cation

40
Q

what are the properties of amidines?

A

strong bases

41
Q

what are guanidines?

A

stronger bases than amidines

42
Q

what makes aniline a weak base?

A

resonance occurs in an uncharged amine

43
Q

how does the effect on aromatic ring increase

A

effect increased if electron-withdrawing group on ortho or para position on the aromatic ring

44
Q

why do aromatic amine are a weaker base than aniline?

A

improved delocalization in free base

45
Q

what effect do electron-donating groups have?

A

increase basicity

46
Q

why does pyridine have a lower basicity than piperidine?

A

pyridine is aromatic with 6p electrons
planar
lone pair of electrons held in sp2 orbital so increased s orbital than piperidine
meaning lone pair of electrons are held closer on nitrogen so less readily bonded to a proton

47
Q

why is pyrrole is a stronger acid than pyridine?

A

the lone pair is part of the delocalized p-system and not available to bond to a proton

drug structure (9 decks)

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