Carbonyl Compounds.pptx

8/9/2019 Carbonyl Compounds.pptx

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Carbonyl Compounds

A2 Chemistry Unit 4


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What functional group do allcarbonyl compounds contain?

δ+ δ-


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What is the aldehyde functionalgroup?


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What is the ketone functionalgroup?


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Name the followingmolecules:

Propanal Methylpropanal

Methanal

Propanone Pentan-3-one Methylbutanone


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Describe and explain the boiling point ofcarbonyl compounds, referring to the type

of bonding.

Methanal is a gas and the other carbonylcompounds are liquid at room temperature

!he molecule are polar" so dipoledipole #orcesas $ell as !an der Waals #orces e%ist bet$eenthem &ntermolecular hydrogen bonding is notpossible because neither aldehydes nor 'etonesha(e a hydrogen atom that is su)ciently δ+

!his causes them to*a(e higher boiling points than al'anes andal'enesa(e lo$er boiling points than alcohols


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Describe and explain the solubilityof carbonyl compounds in water.

!he lo$er members o# both aldehydes and 'etonesare soluble in $ater !his solubility is due to the hydrogen bondingbet$een the lone pair o# electron in the δ- o%ygen in

the carbonyl compound and the δ+ hydrogen in a$ater molecule ,olubility decreases as the numbero# carbons increases because the hydrocarbon tail ishydrophobic

δ+ δ-

δ+

δ+


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Describe the smell of carbonylcompounds.

!he lo$er members o#the homologous series

o# aldehydes ha(epungent odours.

"etones ha(e muchsweeter smells thanaldehydes


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Describe the preparation of aldehydesand gi!e the e#uation for the

preparation of ethanal.

$eagents: Primary alcohol

Potassium dichromate ./&0 in dilute sul#uric acid

Conditions: !emperature o# about 1Cistil o# product as it #orms

%bser!ation: Colour change #rom orange to green as dichromate ./&0 is reduced to chromium.&&&0

Aldehydes are prepared by the partial oxidation o#a primary alcohol


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Describe the preparation of ketonesand gi!e the e#uation for the

preparation of propanone.

$eagents: ,econdary alcohol

Potassium dichromate ./&0 in dilute sul#uric acid

Conditions: eat under re5u%6hen reaction has 7nished" distil o8 product

%bser!ation: Colour change #rom orange to green as dichromate ./&0 is reduced to chromium.&&&0

Aldehydes are prepared by the oxidation o# asecondary alcohol


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aldehydes with(ehling)s*+enedict)s solution and

gi!e an e#uation in!ol!ingethanal.

6hen an aldehyde is warmed $ith

:ehling;s


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aldehydes with ollens) reagentand gi!e an e#uation in!ol!ing

ethanal. !ollens; reagent is made by adding a #e$ drops o# sodiumhydro%ide to sil(er nitrate solution and then dissol(ing theprecipitate in dilute ammonia

6hen a #e$ drops o# !ollens; are added to thealdehyde and the mi%ture is $armed gently" thealdehyde is o%idised =ecause the solution isal'aline the salt o# the carbo%ylic acid is #ormed

!he colourless !ollen;sreagent is reduced togi(e a sil!er mirror

N.+. 6ith 'etones there is no reaction and the solution stays

ld h d i h idi- d


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aldehydes with acidi-edpotassium dichromate /01 and

gi!e an e#uation in!ol!ingethanal.6hen heated $ith the acidi7ed potassiumdichromate the aldehyde is oxidised to a

carboxylic acid

!he orange potassium

dichromate ./&0 isreduced to green Cr .&&&0

N.+. 6ith 'etones there is no reaction and the solution stays orange


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D ib th d ti f


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Describe the reduction of analdehyde, including the e#uation

for the reduction of propanone.$educing agent: >ithiumtetrahydridoaluminate .&&&0" >iAl4 !he 2i'l34 acts as a source o# 3

ions $hich add

on to the 56 carbon atom ? at this point thereactants must be 'ept dry so it is carried out inether solution@e%t" a solution o# a#ueous acid is added $hich

protonates the %

#ormed in the 7rst step

' secondary alcohol is formed.


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Why does 2i'l34 reduce carbonyl

compounds but not alkenes?

>iAl4 is a reducing agent that

reacts speci7cally $ith polar -bonds


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needed for the reaction betweenhydrogen cyanide and a carbonyl

compound.

p B ? this pro(ides the C@- ion catalyst


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Draw the mechanism for the reactionof hydrogen cyanide and ethanal.

2-hydro%y-propanenitrile


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Draw the mechanism for the reactionof hydrogen cyanide and propanone.

2-hydro%y-2-

methylpropanenitrile


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What is the di&erence betweenthe two reactions?

!he ketone reactionhappens at a slower rate


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Why is it important that the p3is neither too high or too low?

it is too high thereare not enough 3CN molecules #or the secondstep

it is too low"there are not

enough CN ions #orthe 7rst step


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acti!ity of the product when

hydrogen cyanide adds on to a

carbonyl compound.

!he product is a racemic mixture o# both

enatiomers so it does not rotate the planeo# plane-polarised light

!his is because the carbonyl compound is planar

around the C9% group so the cyanide ion canattack #rom abo!e or below the plane


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Describe how carbonyl


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Describe how carbonylcompounds react with compounds

containing an 3

N group.

!he lone pair o# electrons on the nitrogen

atom acts a nucleophile and #orms a bond $ith the 56 carbon atom in the C9% group

A water molecule is then lost and a C9N bondis formed

Describe how 4


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Describe how ,4dinitrophenylhydra;ine can be

used to test for a carbonyl group.Add a #e$ drops o# 2"4-dinitrophenylhydraine to a solution o# thecompound

7imple aldehydesand 'etones gi(e ayellow precipitate

'romatic aldehydesand 'etones gi(e anorange precipitate


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reaction between a carbonyl

compound and ,4

dinitrophenylhydra;ine.


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What type of reaction occurs andwhat type of mechanism is it?

Condensationreaction ? $ith the

loss o# a $atermolecule

'dditionelimination

escr e ow you can ma e an pur y a er !a !e


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escr e ow you can ma e an pur y a er !a !eof a carbonyl compound using ,4

dinitrophenylhydra;ine.


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=xplain how this remo!esimpurities.

&n step 2 the deri(ati(e $ill recrystallise butthe impurities $ill remain in solution

!he third step" $ashing $ith cold sol(ent"$ill then rinse o# any impurities that didcrystallise

3ow can the puri-ed product be


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3ow can the puri-ed product beused to identify the original

carbonyl compound?

:ind the melting temperatureand compare to 'no$n data


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What is the reaction of carbonyl


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What is the reaction of carbonylcompounds with iodine in alkali

called?

!he iodo#orm reaction


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What type of carbonyl compoundsundergo the iodoform reaction?

Dthanal and methyl 'etones


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Describe how the iodoform reactionoccurs, including e#uations.

7odium hydroxide solution is added to iodine solution to #orm iodate 01 ions:

!hese substitute into the ?C3> group ne%t to the

C9% group" #orming a C0>C9% group

!he three halogen atoms and the oxygen atom ha(ean electronwithdrawing e8ect $hich weakens and breaks the bond bet$een the t$o carbonatoms" #orming iodoform*


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Write the o!erall e#uation forthe iodoform reaction.

Carbonyl Compounds.pptx

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