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Chemistry > 4.2 carbonyl compounds > Flashcards

4.2 carbonyl compounds Flashcards

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1
Q

carbonyl compounds contain

planar 120 degree

A

> C=O

C is bonded by O by a sigma and a pi bond

bond is polar due to to diff in electronegativity

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2
Q

two types of carbonyl compounds

A

aldehyde - at least one H attached to the carbonyl group

ketone - two carbons attached to the carbonyl

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3
Q

physical properties of carbonyl compounds

boiling point

carbonyls have higher bp and mp than hydrocarbons of similar relative molecular masses

why?

A

carbonyls have london forces and permanent dipole - dipole force between their molecules

hydrocarbons have london forces

carbonyl s have stronger intermoleculaar force than hydrocarbons. more energy is required to break it

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4
Q

physical properties of carbonyl compounds

boiling point

carbonyls have lower bp and mp than alcohols why?

A

alcohols have hydrogen bonding

hydrogen bonding is stronger than london forces and permanent dipole - dipole force

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5
Q

physical properties of carbonyl compounds

solubility

the lower members of both series are soluble in water why?

A

the weak intermolecular forces btwn lower members of carbonyl can be overcome by the hydrogen bonding btwn carbonyl and water

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6
Q

physical properties of carbonyl compounds

smell

lower members of aldehyde
ketone

A

lower members of aldehyde
- pungent odours

ketone
- sweeter than aldehyde

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7
Q

show how hydrogen bonds act btwn ethanl and water

explain why ethanal is more soluble than pentanal in water

A

refer notes pg 2

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8
Q

nucleophilic addition of hydrogen cyanide

reaction with ethanal

eq
reagent
condition
product
reaction type
A

eq notes pg3

reagent: hydrogen cyanide HCN in KCN ( catalyst )
condition: reflux in alkaline solution pH8
product: 2 - hydroxypropanitrile

reaction type: nucleophilic addition

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9
Q

nucleophilic addition of hydrogen cyanide

reaction with ethanal

important step to?

A

increase the carbon skeleton of the original molecule

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10
Q

nucleophilic addition of hydrogen cyanide

reaction with ethanal

mechanism

A

refer notes pg 3

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11
Q

nucleophilic addition of hydrogen cyanide

reaction with aldehyde or asymmetric ketone

product is a racemic mixture

draw mechanism

A

refer to pg 4 exercise 2

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12
Q

nucleophilic addition of hydrogen cyanide

reaction with ethanal

product is a racemic mixture of both optical isomers of 2-hydroxypropanitrile

draw mechanism

A

refer pg 4

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13
Q

nucleophilic addition of hydrogen cyanide

reaction with ethanal

product is a racemic mixture of both optical isomers of 2-hydroxypropanitrile

why?

A

the reactant is planar

do not confuse with reasons from SN1 where carbocation is planar

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14
Q

C=O is nucleophilic addition

C=C is electrophilic addition

why

A

C=O is polar. nucleophiles attack slightly+ C. will repel electrophiles

C=C is non polar. electrophiles attack the electron cloud above and below the sigma bond

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15
Q

nucleophilic addition of hydrogen cyanide

reaction with ethanal

HCN is a weak acid why the reaction occurs more slowly at both high and low concentrations of hydrogen ions

high H+ low pH
low H+ high pH

A

low pH

  • not enough CN- from the base to attack slightly + C in slow reaction
  • less nucleophiles

high pH

  • not enough HCN to regenerate CN- back in fast reaction
  • position of equilibrium shifts to the right
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16
Q

why ketones are less reactive than aldehyde

A

ketones have 2 electron donating group ( CH3 )

steric hindrance

slower reaction

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17
Q

detecting presence of carbonyl

using?
eq
reagent
condition
product
reaction type
observation
A

eq refer notes pg 5

reagent: 2,4 - dinitrophenylhydrazine solution / brady’s reagent
condition: room temp
product: 2,4 - dinitrophenylhydrazone solid

reaction type: nucleophilic addition / elimination

observation: orange to yellow percipitate

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18
Q

detecting presence of carbonyl

reagent: 2,4 - dinitrophenylhydrazine solution
condition: room temp

positive only for?

A

ketone

aldehyde

19
Q

oxidation of aldehydes

acidic condition :
alkaline condition:

what forms

A

acidic: carboxylic acid

alkaline condition: salt of carboxylic acid / carboxylate anion

20
Q

oxidation of aldehydes

common oxidising agent

strong?
weak?

A

strong: KMnO4 and K2Cr2O7 (acidic) specify the acid used

weak:
- blue fehling’s solution
- colourless tollen’s reagent
alkaline

21
Q

oxidation of aldehydes

observations?

K2Cr2O7 acidified with dilute H2SO4
Fehling’s reagent in alkaline and warm gently
Tollen’s reagent in alkaline and warm gently

A

K2Cr2O7 acidified with dilute H2SO4
- orange solution turns green / Cr 3+

Fehling’s reagent in alkaline and warm gently
- blue solution turns colourless and into brick red percipitate / Cu2O cooper (I) oxide

Tollen’s reagent in alkaline and warm gently
- colorless solution turns into a silver mirror in test tube / Ag

22
Q

eq for

oxidation of ethanal in acidified potassium dichromate (VI) solution

oxidation of ethanal in alkaline tollen’s

A

refer pg 7

23
Q

half eq

for silver ions acting as oxidising agent

for copper (II) ions acting as oxidising agent

A

refer pg 7

24
Q

reduction

aldehyde to?

ketone to?

A

primary alcohol

secondary alcohol

25
Q

reduction of aldehyde and ketone

using?

A

LiAlH4

lithium aluminium hydride in dry ether

26
Q

LiAlH4
lithium aluminium hydride in dry ether

what s so good about it?

A

powerful reducing agent

provides strong nucleophiles hydride ion H- to attack C of C=O

27
Q

LiAlH4
lithium aluminium hydride in dry ether

why dry ether

A

LiAlH4 is a powerful reducing agent

provides strong nucleophiles hydride ion H- to attack H slightly + of water instead of C slightly + of C=O

28
Q

reduction of ethanal

eq

A

refer pg8

29
Q

reduction of propanone

eq

A

refer pg 8

30
Q

tri-iodomethane reaction

involves what group?

A

CH3-C=O

Refer pg 8

31
Q

tri-iodomethane reaction

eq
reagent
condition
product
reaction type
observation
A

eq refer pg 8

reagent: iodine in aq NaOH
condition: warm gently
product: sodium salt of carboxylic acid and triiodomethane
observation: yellow ppt and antiseptic smell

32
Q

tri-iodomethane reaction

invovles two steps/reactions

A

substitution
- 3H in CH3 are replaced by iodine atoms

hydrolysis
- the intermediate is hydrolysed to form a yellow ppt of CHI3

33
Q

yellow ppt from unkown compounds
from tri - iodomethane

what is detected?

A

CH3CO-

34
Q

tri-iodomethane reaction

who are involve?

A

methyl ketone

ethanal

ethanol

2nd methyl alcohol

35
Q

why ethanol and 2nd methyl alcohol give a positive result for tri-iodomethane reaction

A

initially oxidised by alkaline iodine solution to ethanal and methyl ketone respectively

react further to form triiodomethane

36
Q

test and identification of a carbonyl compound

how to distinguish two carbonyls with similaar boiling points

A

determining the melting points of their 2,4 - dinitrophenylhydrazone derivatives

37
Q

determining the melting points of their 2,4 - dinitrophenylhydrazone derivatives

test and identification of a carbonyl compound
how to distinguish two carbonyls with similaar boiling points

method

A
  • react carbonyls with 2,4 - dinitrophenylhydrazine solution
  • products are purified by recrystallization and filtered then washed
  • dry the purified product and measure its melting point
  • refer data booklet and compare this melting temp with those known 2,4 - dinitrophenylhydrazine derivatives
  • the melting derivatives can be used to identify the original ketone / aldehyde
38
Q

test to differentiate

aldehyde and ketone

A

oxidation using warmed K2Cr2O7 with dilute H2SO4

aldehyde turns orange to green

ketone remains orange

39
Q

test to differentiate

ketone and ketone

pentan - 2 - one and pentan - 3 - one

A

warm gently with iodine in aq NaOH

pentan - 2 - one forms yellow ppt

and pentan - 3 - one remains brown solution

40
Q

test to differentiate

aldehyde and aldehyde

ethanal and hexanal

A

warm gently with iodine in aq NaOH

ethanal forms yellow ppt

hexanal remains brown solution

41
Q

test to differentiate
alcohol and alcohol

methanol and ethanol

A

warm gently with iodine in aq NaOH

ethanol forms yellow ppt

methanol remains brown solution

42
Q

reactions of aldehyde

A

oxidation

reduction

addition

43
Q

reactions of ketone

A

reduction

addition

Chemistry (9 decks)

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