10. colour by design

Arenes or aromatic compounds

Arenes or aromatic compounds

contain a benzene ring

kekulé structure

benzene ring with alternating single and double bonds which continuously flip

delocalised structure

benzene ring with ring of electrons

kelulé problem

C-C should be longer than C=C bond but is is not proved by x ray diffraction studies.

delocalised model

electrons from p orbital form a delocalised ring

electrophilic substitution of bromine

bromine combines with an alkene but acting as an electrophile attaching to the C=C

subsitution of bromine with benzene

delocalised ring is more stable due to the electrons been more spread out so a catalyst is required for them to react. a hydrogen is swapped with bromine so benzene doesn't have to lose an electron

enthalpy changes prove delocalisation

hydrogenation of cyclohexane with one C=C is -120kJ mol-1 so benzene should be -360kJ mol-1 but instead its -208kJ mol-1

enthalpy change of benzene

-208kJ mol-1 suggests lots of energy needed to break bond and the structure is more stable

benzene warmed with concentrated nitric and sulphuric acids

process to get nitrobenzene with an acid catalyst and a NO2+ electrophile

monotriration

where one NO2 added to benzene when its kept below 55 degrees

quick way to make benzenesulfonic acid

warm benzene to 40 degrees with fuming sulfuric acid for 30 mins. as the fuming acid contains lots of dissolved SO3

slow way to make benzenesulfonic acid

boil benzene under reflux with concentrated sulfuric acid for several hours. as the acid contains H2SO3 which breaks down to SO3

benzenesulfonic acid mechanism

SO3 attacks benzenes delocalised ring due to S been +ve. O -ve then takes h from the benzene where it has bonded and electrons return to the delocalised ring. form of electrophilic substitution

halogen carrier

A catalyst that makes a compound more positive allowing it to bond with benzene

halogen carrier process

catalyst accepts lone pair of electrons from halogen containing polar molecule. polarising a electrophile. sometimes produces a carbocation

carbocation

organic ion with a positive carbon

alkyl group

groups with one H atom less than alkane molecules eg CH3. which bond to other things

reactants to make methylbenzene

reflux chloroalkane and benzene with a halogen carrier (Al3)

how methylbenzene made

• carbocation (CH3+) formed from chloroalkane and AlCl3.

• carbocation reacts with benzene via electrophilic substitution

• AlCl4- reacts with H+ formed regenerating the catalyst and HCl

Friedel-Crafts alkylation

method to attach alkyl group to benzene

acyl group

groups containing C=O

process to join acyl to benzene

Frieda crafts technique but refluxing benzene with acyl chlorine. the electrophile acylium ion CH3CO+ is used and produced.

azo dye

man made dye containing ago group -N=N- which typically joins 2 aromatic groups. these become part pf the delocalised structure and are very stable.

light absorption

causes colour due do defect results from different aromatic groups and amide combinations

couple reaction

type of reaction to make azo dye

process to make azo dye

first diazonium salt made (contains -N+///N-) which is then joined to a aromatic compound

process to make diazonium salt

• nitrous acid is unstable so made in situ from sodium nitrate and hydrochloric acid

• nitrous acid then reacts with phenylamine and hydrochloric acid forming benzendiazomium chloride. below 5℃ or phenol forms

process to make azo dye from diazonium salt and phenol

• phenol dissolved in sodium hydroxide solution to make sodium phenoxide

• added to ice and chilled benzenediazonium chloride/diazonium salt added

• azo dye precipitates once its coupled

colourfast

a dye that won’t wash out or fade in light. depends on bonding between dyes and fibres

dye bonding types

• hydrogen bonding -weak

• instantaneous dipole induced dipole

• ionic bonding between charged groups

• fibre reactive dyes- strongest

hydrogen bonding

bonding between amine (NH2) and alcohol (OH) groups and alcohol (OH) groups on fibres like cotton and cellulose with interactions relating to lone pairs of electrons. Usually liner close fitting molecules for maximum strength

ionic bonding

dyes become acidic when dissolved in water due to SO3- groups, and fibres with NH2 groups become NH3+ groups in acidic conditions, allowing bonding between the two. eg nylon, wool, silk

mordanting

metal ion used to join dye to fabric where both from dative bonds with metal informing chelate complex ions eg Al3+ and Cr3+

chromophores

structures which give a molecule there colour

how chromophores give colour

certain wavelengths absorbed and others reflected, the ones reflected as visible light gives the colour.

chromophore characteristics

contain double or triple bonds, lone electron pairs or benzene rings, these normally form fart of a delocalised system across large part of the molecule.

modifying chromophores

functional groups containing O or N with lone pairs can be added which alters the delocalised system and the colour of the dye

make dyes more water soluble

stabilising functional groups incorporated to dyes like ionic groups eg sulphate ion. these can become polar

covalent bond

where atomic orbitals link up to become molecular orbitals

exited state

when I electron moves up a orbital by absorbing uv or visible light

complementary colours

relationship between the colours absorbed and reflected

single covalent bonds

2 atomic orbitals with 1 electron form 2 molecular orbitals where. only one is filled (2e). the energy gap between orbitals is large so requires high frequency UV to excite electrons

double bond

2 atomic orbitals with 1 electron form 4 molecular orbitals. The energy gap between orbitals is small as there’s 4 so requires low frequency UV to excite electrons

delocalised systems

many molecular orbitals formed which are close in energy levels so electrons only need to absorb very low frequency UV and visible light to be excited. eg benzene

primary alcohol

heating alcohol with a oxidant agent (acidified potassium dichromate VI) makes an aldehyde, the scan further oxidise to form a carboxyl acid. to get a aldehyde you have to distil it immediately

secondary alcohol

reflux a alcohol to with an oxidising agent to make a ketone

Fehlings solution

solution used to test for aldehydes and ketones, which is a complex of copper ii ions dissolved in sodium hydroxide

blue solution

colour or fehlings solution

fehlings solution method

heat (water bath) the solution (2cm3)with the aldehyde or ketone (5 drops), if aldehydes the copper is reduced to become brick red precipitate coper oxide Cu2O

tollens reagent/silver mirror test

reagent to test for aldehydes and ketones

tollens reagent method

• 2cm3 of 0.1 mild-3 silver nitrate

• few drops of dilute sodium nitrate solution forming a light brown ppt

• add few drops of ammonia till down ppt dissolves completely- now made the reagent

• put test tube in hot water bath and add 10 drops of aldehyde or ketone

tollens reagent results

if aldehyde then silver mirror made, if ketone then nothing happens

hydrogen cyanide HCH

a weak acid that partially dissociates in water to from H+ and CN-

hydrogen cyanide reacts with carbonyls by nucleophilic addition

• CN- attacks partially possible C and donates 2e to the O

• H+ from HCH or water bonds to the other O forming OH

• this creates cyanohydrin

naming functional groups

• main functional group is the suffix- end

• others added as prefix- start

• alphabetical order

polyfunctional molecule

molecule with many functional groups

testing for polyfunctional molecules

• use multiple solutions to test

• further test melting/boiling point to tell if there is one or multiple compounds

addition reaction

reaction where 2 molecules join together by breaking a double bond, eg alkenes, COOH and C=O

elimination reaction

removal of a functional group releasing it as part of a small molecule, often forming double bond, eg -halogen (H-halogen, eliminated) or -OH (H2O eliminated)

substation reaction

functional groups are swapped eg -halogen, -OH, -benzne

condensation reaction

2 molecules join releasing water, eg -COOH, -COCl, -CONH2

hydrolysis reaction

water used to slip a molecule into 2, eg -COO-, CO-O-CO-

oxidation reaction

loss of electrons, where a molecule typically gains oxygen or loses hydrogen, eg as shown in picture

reduction reaction

gain of electrons typically gaining. hydrogen or losing oxygen eg as shown in picture

bromine water test

test for alkenes/double bonds, where a positive result goes colourless to orange. 2:2cm3 of each and shake

acidified potassium dichromate

10 drops of alcohol to 2cm3 of test solution, warm and watch for colour change

• primary- orange to green aldehyde (if further heating oxidised to carboxylic acid)

• secondary- orange turns to green Ketone

• tertiary- nothing

test for primary vs secondary alcohol

collect some of the product from adding acidified potassium dichromate by using distillation

test for which alcohol with tollens reagent or fehlings solution.

included in description of how to make something

• special procedures

• conditions needed

  • safety precautions

retrosynthesis

method of backward planning a practical

• identify functional groups

• identify any bonds made between groups

• further split up any molecules further

fatty acids

carboxylic acids with long hydrocarbon chains on end, saturated with no double bonds or unsaturated with double bonds. test for with bromine water

triglycerides

• animal and vegetable fats and oils.

• contain ester -COO- 3 times.

• made with glycerol and 3 fatty acids

• 2 OH on glycerol link with 3 OH on fatty acids in condensation reaction

mobile phase

phase in GLC where its a solid or viscous liquid with a high boiling point coating a porous support inside a coiled tube in a oven

mobile phase

phase in GLC which is an inert carrier gas

GLC process

• sample injected into gas stream

• compounds cycle through dissolving in stationary and evaporating into mobile phase

• time dissolving depends on there solubility and effects how ling it takes to reach detector

retention time

Time taken to reach detector in GLC a

relative amount of a substance

area under a peak

gas liquid chromatography mass spectroscopy

sample separated by GLC then fed into a mass spectrometer to identify each component

fibre reactive dyes

reactive group on dye forms a bridge with fibre groups like -OH and -NH-

instantaneous dipole induced dipole bonds

dyes with few polar groups are suspended in water and form weak bonds with the fibre, no OH or NH groups