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Chemistry > Topic 17 - PPQs > Flashcards

Topic 17 - PPQs Flashcards

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1
Q

What does brady’s test for?

A

C=O associated with ONLY aldehydes and ketones

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2
Q

product of a positive test of 2-4 dnph contains which bond?

A

C=N

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3
Q

reagents and conditions for converting ethanal (by two step synthesis) to 2-hydroxypropanoic acid

A

HCN in presence of KCN

dilute HCL, under reflux

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4
Q

What does H- have

A

a lone pair

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5
Q

mechanism for reduction of propanone to propan-2-ol

A

step 1: H- has lone pair, curly arrow form H- to C in C=O, arrow from C=O bond to O, dipoles

step2: dipoles on water, curly arrow from O- to H in water, curly arrow from O-H bond to O in water, lone pair on O-

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6
Q

test to distinguish between carboxylic acid and alcohol

A

sodium carbonate - fizzing if carboxylic acid (production of CO2)

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7
Q

explain why the order of boiling points is this

ethanoic acid > ethanol > ethanal [3]

A

mp1 - ethanal has no H bonds
mp2 - H bonds in ethanol are stronger than london forces in ethanal
mp3 - ethanoic acid forms dimers

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8
Q

what intermolecular forces are present in:

  • ethanal
  • ethanol
  • ethanoic acid
A
  • london forces
  • london forces, ,H bonds
  • london forces, , H bonds, form dimers

XXXXX

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9
Q

Fehlings or…

A

benedicts

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10
Q

what do u do w fehlings/benedicts

A

warm with

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11
Q

Explain why it is necessary to use HCN and KCN in the carbonyl + HCN mechanism?

A

the KCN provides the :CN- nucleophile

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12
Q

explain why the product of the carbonyl + HCN is not optically active

A
  • bonds around C=O planar
  • nucleophile attacks from both sides (above and below)
  • forming a racemic mixture
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13
Q

other than spectroscopy how would you use ppt from a chemical test to identify sm

A
  • measure melting point

- compare against known data

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14
Q

technique used to purify product of test with 2-4dnph

A

recrystallisation

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15
Q

explain why old stocks of aldehydes often react with sodium carbonate solution

A

they contain carboxylic acids which have formed by oxidation of the aldehydes (from the air)

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16
Q

carboxylic acid + sodium carbonate

A

salt + water + CO2

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17
Q

butanoic acid as an acyl chloride

A

butanoyl chloride

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18
Q

two conditions for

alcohol + carboxylic acid —-> ester + water

A
  • H2SO4

- HEAT

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19
Q

identify another chemical that could be added to methanol to make methyl butanoate

A

butanoyl chloride

because alcohol + acyl chloride –> ester + HCl

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20
Q

state 2 advantages of and 1 disadvantage

acyl chloride + alcohol —> ester + HCl
VS
carboxylic acid + alcohol –> ester + water

A

advantages of acyl chloride + alcohol —> ester + HCl

1) goes to completion
2) no catalyst needed

disadvantage
1) acyl chloride difficult to store and more expensive

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21
Q

Naming carboxylic acids - which C is the first C

A

the carbon in the C=O bond

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22
Q

where is the hydrogen bond from and to

A

from the O-H bond to the IIIIIIIIII between the H and lone pair on oxygen

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23
Q

Describe how london forces are formed

A

instantaneous dipole

induced dipole

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24
Q

explain boiling point differences between straight chain and branched chain alcohols

A
  • straight chain higher
  • because branching weakens london forces
  • because less SA so molecules can’t get as close
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25
Q

the oxidation of an alcohol with sodium dichromate (VI) could involve either reflux or distillation - why

A

the alcohol can only be oxidised to a ketone/ cannot be further oxidised/ cannot be oxidised to a craboxylic acid

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26
Q

what functional group reacts with acidified potassium manganate (VII) and what is produced

A

C=C (alkene)

a diol

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27
Q

why might u not be able to oxidise an alcohol with acidified potassium manganate (VII)

A

any C=C bonds will react to form a diol instead

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28
Q

in water why is hexan-1-ol less soluble than ethanol

A

london forces between hexan-1-ol molecules are stronger than those between ethanol molecules

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29
Q

think about what heptan-2-one would look like

A

good job

30
Q

iodoform test, remember to state

A

alkali is NaOH

31
Q

what to remember about drawing HCN in the carbonyl + HCN mechanism

A

include the triple bond and do the curly arrow from the H-C bond to the triple bond

32
Q

explain why the solution produced does not rotate plane polarised light?

A
  • :CN- can attack w equal probability from either side
  • produces a racemic mixture
  • bonds surrounding the carbonyl group are planar
33
Q

equation for iodine and propanone in presence of acid

A

CH3COCH3 + I2 –> CH3COCH2I + HI

34
Q

Why does the rate of reaction increase as the recation between iodine and propanone proceeds

A

HI produced which catalyses the reaction

35
Q

identify organic product formula from reaction between iodine and propanone in alkali conditions

A
  • CHI3

- CH3COONa

36
Q

iodine + propanone in alkali conditions

two observations

A
  • yellow precipitate

- antiseptic smell

37
Q

iodine + propanone in alkali conditions is essentially the same as

A

iodine and alkali reaction to test for methyl ketones

38
Q

explain why water is an unsuitable solvent for reduction reactions

A

LiAlH4 is very reactive with water

39
Q

state two uses of 2-4dnph

A
  • prepare a derivative

- test for C=O associated with ketones and aldehydes

40
Q

if sm is going towards sm in a mechanism dont forget

A

the bloody SECOND CURLY ARROW

41
Q

alcohol + KOH

type of reaction

A

elimination

42
Q

Name all of the intermolecular forces between glucose molecules

A

london forces between all atoms

permanent dipole - permanent dipole forces between delta positive C and delta negative O

H bonding between delta positive H and another oxygen

43
Q

explain why glucose is very soluble in water (3)

A
  • forms hydrogen bonds with water
  • has lots of OH groups
  • energy released forming new H bonds makes up energy used to break H bonds in water
44
Q

equation for formation of ethanol from ethene

A

C2H4(g) + H2O(g) —> C2H5OH(aq)

45
Q

explain why propanal has a lower boiling point than propanol

A

propanal has london forces and permanent dipole-permanent dipole

propanol has london forces, permanent dipole-permanent dipole and H bonds

H bonds are strongest

46
Q

if it says describe a CHEMICAL test what doe sit mean

A

like another chemical like carbonyl or sm NOT AND INDICATOR

47
Q

describe a CHEMICAL test to distinguish between propan-1-ol and propanal

A

positive test for propan-1-ol

  • add PCl5
  • misty white fumes
48
Q

what to remember about writing oxidation or reduction equations

A

BALANCE THE [O] or [H]

49
Q

describe how reflux ensures an aldehyde initially produced is further oxidised to a carboxylic acid

A

aldehyde condensed

50
Q

explain why H bonds do not form between aldehyde molecules

A

they have no H bonded to an oxygen atom

51
Q

How to test for an -OH group without using PCl5

A

Na

effervescence

52
Q

difference between 2-hydroxypropanoic acid in sour milk and muscles that gives rise to difference in optical activity

A
  • 2-hydroxypropanoic acid formed in muscles is a single enantiomer
  • 2-hydroxypropanoic acid formed in sour milk is a racemic mixture
53
Q

X

A
  • racemic mixture not formed
  • bc nucleophile attacks from only one side of the molecule
  • so reaction is Sn2
54
Q

explain why the 2-hydroxypropanoic acid formed from ethanal exhibits no optical activity

A
  • racemic mixture
  • bc aldehyde group was planar
  • so CN attacked from either side w equal probability
55
Q

test that tests positive for ethanal but not 2-hydroxypropanoic acid

A

fehlings, red ppt

56
Q

test that tests positive for test that tests positive for 2-hydroxypropanoic acid but not ethanal

A

sodium carbonate

CO2 produced

57
Q

how can u tell sulfuric acid is in excess when added to salicylic acid to precipitate it out of a solution

A

no more precipitate formed

58
Q

why is salicylic acid sparingly soluble in water

A

because of

  • london forces between the rings
  • H bonds between salicylic acid and water
59
Q

bonds around C=O are planar means

A

no optical activity and racemic mixture is produced

60
Q

suggest the type of reaction if a nitrile is being converted to a carboxylic acid?

A

acid hydrolysis

nitrile + water + acid —> carboxylic acid + NH4Cl

61
Q

give the wave number, shape and bond its due to of the peak present in a carboxylic IR but not an aldehyde

A

3750-2500
broad
due to the -OH bond

62
Q

in a carboxylic acid spectrum what is the tall thin peak due to

A

the C=O

63
Q

why might a peak in a carboxylic acid due to C=O not be used to distinguish between a carboxylic acid and an aldehyde?

A
  • the C=O aldehyde range is 1740 - 1720
  • the C=O carboxylic acid range is 1725 - 1700

so peaks cannot distinguish between two compounds because they overlap (IF THEY OVERLAP - CHECK DIAGRAM OF Q GIVEN)

64
Q

mass spec of carboxylic acid P has m/z = 43, draw the structures of the two species that could give this peak

A
  • draw ions (must be able to be formed from being broken off from original molecule) which rfm add up to 43
65
Q

what bonds are broken and what bonds are made in an esterification reaction

A

bonds broken - C-O, O-H

bonds made - C-O, O-H

66
Q

if

bonds broken - C-O, O-H
bonds made - C-O, O-H

why might the change in enthalpy still not be EXACTLY zero?

A

bond enthalpies differ

67
Q

carbonyl + HCN mechanism

low pH:
high pH:

A

low pH - very few CN-

high pH - very few HCN

68
Q

explain why the presence of an alcoholic -OH group cannot be confirmed in the IR for a carboxylic acid

A

the -OH absorptions for alcohol and carboxylic acid overlap

69
Q

quick proton NMR recap

A

number of peaks = number of H environments

look at each environment and count how many H’s attached to the adjacent carbon (no. H’s + 1 = splitting pattern)

70
Q

why is it a singlet

A

no H atom on the adjacent C

71
Q

when would you expect sm to NOT have optical isomers

A

if it doesn’t have a chiral centre

Chemistry (37 decks)

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