Chemrevise A2 Organic

reducing agents for aldehydes and ketones - what do they provide?

LiAlH4 or NaBH4 - provides source of H- hydride ions attracted to delta +ve carbon

(catalytic hydrogenation - H2 and Ni catalyst)

are carboxylic acids water soluble?

yes up to C4 because they form H bonds

what is methanoic acid oxidised to?

HOCOOH

conditions for esterification

COOH + OH in presence of acid catalyst

uses of esters

perfumes, flavourings, solvents, plasticisers

are esters water soluble?

no, they don’t form H bonds

hydrolysis of esters conditions - which has a better yield?

NaOH or HCl both UNDER REFLUX

HCl has a weak yield, reaction is reversible

NaOH has a better yield, reaction goes to completion - anion is resistant to attack by weak nucleophiles

how does acid strength vary as more R groups are added to a carboxylic acid

less strong, electron density pushed onto COO^- making it more negative and less stable

CH3COO^- Na⁺ + HCl → ?

CH3COOH + NaCl

what is solubility in wate controlled by in a compound?

is benzoic acid soluble

whether the polar or non polar part is of greater importance

no - even though it forms H bonds, the non polar benzene ring takes priority

what are fats and oils?

esters of glycerol and long chain carboxylic acids (fatty acids)

when hydrolysed with NaOH or HCl what do veg oils and animal fats form

soap and glycerol

glycerol and fatty acids

uses of glycerol, is it soluble?

very soluble

cosmetics, food and glue

what is biodiesel?

mixture of methyl esters of long chain carboxylic acids

how is vegetable oil converted to biodiesel?

methanol + strong acid catalyst

how is biodiesel carbon-neutral?

any carbon dioxide released from burning the plant would have been extracted by the plant from the air in photosynthesis

which is more reactive acyl chlorides/acid anhydrides or carboxylic acids? why?

acid anhydrides/acyl chlorides - Cl and -OCOCH3 are good leaving groups

what is formed when acid anhydrides react with water, alcohols, ammonia and primary amines ?

• carboxylic acid

• ester + carboxylic acid

• primary amide + CH3COO - NH4+

• secondary amide + [CH3NH3 ]⁺ [CH3COO ]^-

what is formed when acyl chlorides react with water, alcohols, ammonia and primary amines?

• carboxylic acid and HCl

• ester and HCl

• primary amide + NH4Cl (CONH)

• secondary amide and RNH3⁺Cl^- (CONH)

pros of ethanoic anhydride vs ethanoyl chloride?

• less corrosive

• less vulnerable to hydrolysis

• cheaper

reasons for loss of yield in recrystallisation

• crystals lost when filtering/washing

• side reactions

• product stays in solution after recrystallisation

melting point observations of an impure substace

lower than data book value and over a range of temperatures

benzene and kekule shape

H-C-C bond angle

planar

120^o

how do primary aliphatic amines acts as bronsted-lowry bases?

lone pair on N readily available to accept a proton + form a dative covalent bond - weak bases only low conc. of OH- ions produced

why are primary aliphatic amines stronger than ammonia?

electron releasing alkyl groups push electrons towards N - lone pair on N more readily available to accept protons

order of base strength

Aromatic amines < ammonia< primary amines< tertiary amines< secondary amines

why is the base strength of aromatic amines weaker?

lone pair on N is delocalised with ring of electrons in benzene - lone pair is less available on N

amine + acid (is it water soluble)

how can you convert it back?

ammonium salt - ionic salts so are soluble in water

add NaOH

why is forming primary amines by nucleophilic sub not a good method?

how can we improve this, and how can we promote formation of 4^o ammonium salt?

lone pair on N still available, further sub reactions, product would have to be separated

use excess ammonia, maximises amount of primary amine

excess halogenoalkane

use of 4o ammonium salts

cationic surfactants - used in fabric softeners, hair conditioners and sewage flocculants to reduce surface tension

describe an efficient method for the formation of 1^o amines including its disadvantages

halogenoalkane → nitrile (KCN in aqueous ethanol)

reduce nitrile to amine with H2 and Ni catalyst or LiAlH4 in dry ether

two step reaction may lower yield, KCN is toxic

describe the conditions to reduce nitrobenzene to aromatic amines

state what ionic salt is formed and what it can be reacted with to produce

H2 and Ni catalyst Sn and HCl, heating (reduction)

C6H5NH3⁺Cl^- + NaOH → phenylamine

use enthalpies of hydrogenation to describe the thermodynamic stability of benzene

• expected 3x enthalpy hydrogenation of cyclohexene

• in benzene enthalpy of hydrogenation is less → more thermodynamically stable

toxicity of benzene and a substitute

benzene is a carcinogen

methylbenzene is less toxic and reacts more readily as the methyl group releases electrons - more attractive to electrophiles

what occurs at temperatures higher than 60oC in the nitration of benzene

a second nitration

effect of delocalisation on: chlorobenzene, phenol, phenylamine

• C-Cl bond is stronger, Nusub and elim reactions do not occur, electron rich benzene repels nucleophiles

• C-O bond stronger, O-H bond weaker - does not act like an alcohol, is more acidic, does not oxidise

• less basic than aliphatic amines, lone pair on N less available to accept protons

addition polymer definition - why are polyalkenes inert?

unsaturated monomers react to form a polymer

strong C-H and C-C bonds, non polar - not biodegradable

what is condensation polymerisation?

two different monomers added together and small molecule formed (like water)

terylene monomers and uses

• benezene-1,4-dicarboxylic acid + ethane-1,2-diol

• clothing and tire cords

nylon 6,6 monomers and uses

• hexanedioic acid + hexane-1,2-diamine

• ropes, fabric, carpet

kevlar monomers and uses

• benzene-1,4-dicarboxylic acid + 1,4-diaminobenzene

• bulletproof vests, car tyres - lightweight but very strong

condensation polymerisation hydrolysis - acid and alkali products

forms original monomers: if acid amine group is NH3+, if alkali, COOH group is COO-

which has a higher m.p. polyamides or polyesters and why

polyamides, they have H bonds between strands

optical activity of amino acids

all amino acids except glycine and optical isomers - they rotate plane polarised light

what are acidic/basic amino acids?

AAs that have a second NH2 or COOH group as R group

why do AAs have a high mp?

they exist as dipolar zwitterions, so they have ionic interactions that increase mp and are therefore solid

conditions for hydrolysis of a dipeptide - how can you detect which AAs were in the dipeptide?

conc. HCl under reflux

TLC

protein structure: 1^o, 2^o, 3^o, 4^o

• 1^o structure: sequence of amino acids joined together in condensation reaction by peptide links

• 2^o structure: α-helix - 3D corkscrew arrangement held in place by H bonds (H of N^δ-—H^δ+ and –O of C^δ+=O^δ-)

  • or β-Pleated Sheet - parallel strands

• 3o structure: folding of 2^o structure into more complex shapes

  • involves hydrogen bonding, sulfur-sulfur bonds and ionic interactions - cysteine forms sulfur bridges

acidified silver nitrate + chloroalkane or acyl chloride

chloroalkane - slow formation of AgCl

acyl chloride - vigorous reaction, steamy HCl fumes, rapid white ppt of AgCl

describe TLC

• thin-layer chromatography (TLC) – a plate is coated with a solid and a solvent moves up the plate

gas chromatography - process, what info it gives us, factors that can be changed

• a column packed with a solid/solid coated with liquid, gas is passed through the column at high temp. under pressure -

• liquid is stationary phase, inert gas is mobile phase

• separates mixtures of volatile liquids

• tells us how many components there are by the no. of peaks, abundance of substance (proportional to area under peak)

• factors changed - temperature, column length, flow rate

GC can be connected to MS, IR or NMR for further detection

what does a solid phase separate by and what does a liquid phase separate by in chromatography?

• solid by adsorption

• liquid by relative solubility

if the stationary phase is polar, the mobile phase is non polar

what would you do to identify components of a mixture if they both had the same solubility?

two directional chromatography

column chromatography - process and HPLC phases

• A glass tube is filled with the stationary phase silica or alumina in powder form to increase the surface area.

• A filter or plug is used to retain the solid in the tube. Solvent (mobile phase) is added to cover all the powder.

• The mixture to be analysed is dissolved in a minimum of a solvent and added to the column.

• a solvent or mixture of solvents is then run through the column.

• The time for each component in the mixture to reach the end of the column is recorded (retention time)

HPLC mobile phase liquid, stationary phase solid silica

why is a large excess of some reactants used in reactions when determining order

the conc. of that reactant is virtually constant and does not affect rate

how can you calculate the initial rate of reaction from a graph of amount of product/time ?

tangent at t = 0 and calculate m

what happens in the iodine clock experiment?

hydrogen peroxide reacts with iodide ions to form iodine. limited amount thiosulfate ions then immediately react with iodine formed

once the thiosulfate is used up the excess iodine turns starch blue black

H2O2 (aq) + 2H+ (aq) + 2I– (aq) → I2 (aq) + 2H2O(l)

2S2O3 2– (aq) + I2 (aq) → 2I– (aq) + S4O6 2– (aq)

how do you calculate k from a graph of [X]/time?

k = m

what is the effect of a Cl group and a CH3 group?

Cl group electron withdrawing - makes group more electron deficient, weakens O-H bond

CH3 electron releasing - pushes electrons towards other group, less electron deficient