Chemistry Organic

define repeat unit

the specific arrangement of atoms in the polymer molecule that repeats over and over again

molecular formula of propene

C₃H₆

uses of propene

children’s toys, packing crates, guttering, uPVC windows, fibre for ropes

molecular formula of phenylethenestyrene

C₈H₈

molecular formula of tetrafluoroethene

C₂F₄

name an environmental issue with the use of alkene based polymers

non-biodegradable

disadvantage of recycling polymers

discarded polymers have to be sorted by type

disadvantage of PVC recycling

PVC releases hydrogen chloride when burnt which is a corrosive gas

why are some polymers difficult to recycle

some polymers are derived from petroleum or natural gas which means it has a high stored energy value

steps of using waste polymers as fuel

1) waste polymers are incinerated

2) this produces heat

3) this heat generates steam

4) this steam drives a turbine which produces electricity

define feedstock recycling

the chemical and thermal processes that can reclaim monomers, gases, or oil from waste polymers

advantage of feedstock recycling

able to handle unsorted and unwashed polymers

define bioplastics

plastics produced from plant starch, cellulose, plant oils, and proteins that offer a renewable and sustainable alternative to oil based products

define compostable polymers

polymers based on poly(lactic acid) which degrade and leave no visible or toxic residues

define photodegradable polymer

polymer which degrades by absorbing UV

2bp 0lp

linear 180

3bp 0lp

trigonal planar 120

2bp 1lp

bent 119

4bp 0lp

tetrahedral 109.5

3bp 1lp

trigonal pyramidal 107

2bp 2lp

angular 104.5

5bp 0lp

trigonal bipyramdidal 90

4bp 1lp

seesaw 119, 89

why are alkenes more reactive than alkanes

1) alkenes have a pi bond 2) pi electron density is concentrated above and below the plane of the sigma bond 3) pi electrons are more exposed than the electrons in the sigma bond therefore the pi bond readily breaks

name 4 substances alkenes have addition reactions with

1) hydrogen in the presence of a nickel catalyst 2) halogens 3) hydrogen halides 4) steam in the presence of an acid catalyst

describe hydrogenation of alkenes

when an alkene is mixed with hydrogen and passed over a nickel catalyst at 423K an addition reaction takes place to form an alkane

describe halogenation of alkenes

alkenes react with the halogens chlorine or bromine at room temperature to form haloalkanes

describe a positive test for unsaturation

bromine water (orange) + alkene = haloalkane (colourless)

describe addition reactions of alkenes with hydrogen halides

alkenes react with gaseous hydrogen halides at room temperature to form multiple haloalkanes

how do addition reactions of alkenes with hydrogen halides occur when the alkene is a gas

reaction takes place when the two gases are mixed

how do addition reactions of alkenes with hydrogen halides take place when the alkene is a liquid

the hydrogen halide is bubbled through it

describe hydration reactions of alkenes

alkenes react with steam in the presence of a phosphoric acid catalyst H₃PO₄ to form alcohols

diagram of formation of a pi bond

define homolytic fission

each of the bonded atoms takes one of the shared pair of electrons from the bond

define heterolytic fission

one of the bonded atoms takes both of the electrons from the bond

define reaction mechanism

how a reaction takes place

define addition

two reactants join together to form one product. eg. double bonds are broken to form single bonds

define substitution

an atom or group of atoms is replaced by a different atom or group of atoms

define elimination

the removal of a small molecule from a larger one so one reactant forms two products.

define nucleophile

an atom or compound with a negative or partial negative charge which is able to form a covalent bond by donating a lone pair of electrons

define electrophile

an atom or group of atoms that is attracted to a region of high electron density and can accept a pair of electrons

define free radical

an atom or group of atoms which have a single unpaired electron

functional group of aldehyde

-CHO

functional group of ketone

-CO-

why do aldehydes and ketones undergo nuceophilic addition

contain C=O bond

C=O is polar because oxygen is more electronegative than carbon

nucleophiles are attracted to and attack the delta positive C atom

aldehyde = primary alcohol

NaBH₄ / H₂O

reduction

ketone = secondary alcohol

NaBH₄ / H₂O

reduction

reduction of an aldehyde

Aldehyde + 2[H] → Primary alcohol

reduction of a ketone

Ketone + [H] → Secondary Alcohol

what chemicals are used in place of HCN

NaCN/ H₂SO₄

diagram of reaction of aldehyde with HCN

aldehyde/ ketone = hydroxynitrile

HCN (or NaCN/ H₂SO₄)

diagram of mechanism for the nucleophilic addition of a carbonyl compound

diagram of mechanism for the reaction of carbonyl compounds with NaCN/H⁺

steps of testing for the carbonyl group in aldehydes and ketones

1) add 5cm³ of a solution of 2,4-DNP in excess into test tube

2) pipette 3 drops of unknown compound and leave to stand

3) if no crystals form add a few drops of H₂SO₄

4) yellow/orange precipitate forms = C=O present

steps of testing for aldehyde

1) add 3cm³ AgNO₃ (aq) into clean test tube

2) add NaOH (aq) into the AgNO₃ until a brown precipitate of AgO is formed

3) add dilute ammonia solution until the brown precipitate just dissolves to form a clear colourless solution = Tollens’ reagent

4) pour 2cm³ of unknown solution into clean test tube

3) add 2cm³ Tollens’ reagent

3) leave to stand in beaker of warm water 50°C for 15 minutes. silver mirror = aldehyde present

why does a silver mirror form in the presence of an aldehyde

Tollens’ reagent contains Ag⁺ ions which act as an oxidising agent in the presence of ammonia

Ag⁺ ions are reduced to silver as the aldehyde is oxidised to a carboxylic acid

steps to melting point analysis of carbonyl compounds

1) filter impure yellow/orange solid to separate the solid precipitate from the solution

2) recrystalise the solid to produce a pure sample of crystals

3) measure and record the melting point of the purified 2,4-DNP

4) compare the mp to a database to identify the original compound

solubility of carboxylic acids

C=O AND O-H bonds are polar

form hydrogen bonds with water

carboxylic acids with up to 4 C atoms are soluble in water

as number oc C atoms increases, solubility decreases as the non-polar C chain has a greater effect on overall polarity

strength of carboxylic acids

weak acids

partially dissociates in water

HCOOH (aq) = H⁺(aq) + HCOO^- (aq)

functional group of carboxylate

define a hydrogen bond

a type of permanent dipole-dipole interaction found between molecules containing an electronegative atom with a lone pair of electrons and a hydrogen atom attached to an electronegative atom

explain why ice is less dense than water

1) when water freezes hydrogen bonds hold water molecules apart in an open lattice structure 2) the water molecules in ice are further apart than in water

benefits of ice being less dense than water in lakes and ponds

the ice acts as an insulating layer and prevents the water from freezing solid

explain why water has a relatively high melting and boiling point

1) all molecules have London forces between them 2) hydrogen bonds are extra forces over and above the London forces 3) a larger quantity of energy is required to break hydrogen bonds in water

define hydrocarbon

a compound containing carbon and hydrogen only

define homologous series

a family of compounds with similar chemical properties whose successive members differ by the addition of a -CH2 group

define functional group

part of the organic molecule that is largely responsible for the molecule’s chemical properties

alcohol

hydroxy/ -ol

alkene

-ene

aldehyde -CHO

-al

ketone -C(CO)C-

-one

carboxylic acid -COOH

-oic acid

ester -COOC-

-oate

acyl chloride -COCl

-oyl chloride

amine -NH2

amino-/ -amine

nitrite -CN

-nitrite

define aliphatic

carbon atoms are joined to each other in unbranched or branched chains or non-aromatic rings

define alicyclic

carbon atoms are joined to each other in cyclic structures with or without branches

define aromatic

some or all of the carbon atoms are found in a benzene ring

define alkane

containing single carbon-to-carbon bonds

define alkene

containing at least one double carbon-to-carbon bond

define alkyne

containing at least one triple carbon-to-carbon bond

alkyl

-yl

alkane → haloalkane

halogen/ UV

radical substitution

alkene = alkane

H₂

Ni catalyst

423K

addition

alkene = haloalkane

hydrogen halide

RTP

addition

alkene = alcohol

H₂O (g)/ H₃PO₄

addition

alcohol = alkene

conc H₂SO₄

elimination

haloalkane = alcohol

NaOH (aq)

reflux

nucleophilic substitution

alcohol = haloalkane

sodium halide and H₂SO₄

reflux

nucleophilic substitution

primary alcohol = carboxylic acid

K₂Cr₂O₇/ H₂SO₄

reflux

oxidation

primary alcohol = aldehyde

K₂Cr₂O₇/ H₂SO₄

distil

oxidation

secondary alcohol = ketone

K₂Cr₂O₇/ H₂SO₄

reflux

Oxidation state of Group 1 metals

Always +1