what intermolecular forces are present in: - ethanal - ethanol - ethanoic acid

- london forces - london forces, ,H bonds - london forces, , H bonds, form dimers XXXXX

Topic 17 - PPQs Flashcards by Hana bashir

What does brady’s test for?

C=O associated with ONLY aldehydes and ketones

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

C=N

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

HCN in presence of KCN

dilute HCL, under reflux

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What does H- have

a lone pair

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mechanism for reduction of propanone to propan-2-ol

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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test to distinguish between carboxylic acid and alcohol

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

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explain why the order of boiling points is this

ethanoic acid > ethanol > ethanal [3]

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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what intermolecular forces are present in:

ethanal
ethanol
ethanoic acid

london forces
london forces, ,H bonds
london forces, , H bonds, form dimers

XXXXX

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Fehlings or…

benedicts

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what do u do w fehlings/benedicts

warm with

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

the KCN provides the :CN- nucleophile

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

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

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

measure melting point

- compare against known data

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

recrystallisation

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

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

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carboxylic acid + sodium carbonate

salt + water + CO2

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butanoic acid as an acyl chloride

butanoyl chloride

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two conditions for

alcohol + carboxylic acid —-> ester + water

H2SO4

- HEAT

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

butanoyl chloride

because alcohol + acyl chloride –> ester + HCl

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state 2 advantages of and 1 disadvantage

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

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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Naming carboxylic acids - which C is the first C

the carbon in the C=O bond

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where is the hydrogen bond from and to

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

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Describe how london forces are formed

instantaneous dipole

induced dipole

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explain boiling point differences between straight chain and branched chain alcohols

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

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

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

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

C=C (alkene) a diol

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

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

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

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

think about what heptan-2-one would look like

good job

iodoform test, remember to state

alkali is NaOH

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

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

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

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

equation for iodine and propanone in presence of acid

CH3COCH3 + I2 --> CH3COCH2I + HI

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

HI produced which catalyses the reaction

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

- CHI3 | - CH3COONa

iodine + propanone in alkali conditions two observations

- yellow precipitate | - antiseptic smell

iodine + propanone in alkali conditions is essentially the same as

iodine and alkali reaction to test for methyl ketones

explain why water is an unsuitable solvent for reduction reactions

LiAlH4 is very reactive with water

state two uses of 2-4dnph

- prepare a derivative | - test for C=O associated with ketones and aldehydes

if sm is going towards sm in a mechanism dont forget

the bloody SECOND CURLY ARROW

alcohol + KOH | type of reaction

elimination

Name all of the intermolecular forces between glucose molecules

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

explain why glucose is very soluble in water (3)

- 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

equation for formation of ethanol from ethene

C2H4(g) + H2O(g) ---> C2H5OH(aq)

explain why propanal has a lower boiling point than propanol

propanal has london forces and permanent dipole-permanent dipole propanol has london forces, permanent dipole-permanent dipole and H bonds H bonds are strongest

if it says describe a CHEMICAL test what doe sit mean

like another chemical like carbonyl or sm NOT AND INDICATOR

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

positive test for propan-1-ol - add PCl5 - misty white fumes

what to remember about writing oxidation or reduction equations

BALANCE THE [O] or [H]

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

aldehyde condensed

explain why H bonds do not form between aldehyde molecules

they have no H bonded to an oxygen atom

How to test for an -OH group without using PCl5

Na | effervescence

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

- 2-hydroxypropanoic acid formed in muscles is a single enantiomer - 2-hydroxypropanoic acid formed in sour milk is a racemic mixture

- racemic mixture not formed - bc nucleophile attacks from only one side of the molecule - so reaction is Sn2

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

- racemic mixture - bc aldehyde group was planar - so CN attacked from either side w equal probability

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

fehlings, red ppt

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

sodium carbonate CO2 produced

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

no more precipitate formed

why is salicylic acid sparingly soluble in water

because of - london forces between the rings - H bonds between salicylic acid and water

bonds around C=O are planar means

no optical activity and racemic mixture is produced

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

acid hydrolysis | nitrile + water + acid ---> carboxylic acid + NH4Cl

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

3750-2500 broad due to the -OH bond

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

the C=O

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

- 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)

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

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

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

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

if bonds broken - C-O, O-H bonds made - C-O, O-H why might the change in enthalpy still not be EXACTLY zero?

bond enthalpies differ

carbonyl + HCN mechanism low pH: high pH:

low pH - very few CN- | high pH - very few HCN

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

the -OH absorptions for alcohol and carboxylic acid overlap

quick proton NMR recap

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)

why is it a singlet

no H atom on the adjacent C

when would you expect sm to NOT have optical isomers

if it doesn't have a chiral centre