Organic Chemistry

Functional Group

Functional Group

A functional group is a specific group of atoms within a molecule that determines the molecule's chemical properties and reactivity.

Homologous Series

Same functional group and each successive member has an additional -CH2 group

Structural Isomers

Molecules with the same molecular formula but different structural formulae

Functional Group Isomers

Same molecular formula but different functional groups

Chain isomers

Same molecular formula but differ in arrangement of the hydrocarbon chain

Positon isomers

Same molecular formula but functionl group position changes

Stereoisomers

Same structural formula but the atoms are arranged differently in space

Rotation of single covalent bond vs double/triple

Single bond - fully rotational

Double/triple - restricted

Requirements for Cis/Trans isomers

Carbon- Carbon double bond

Carbon atoms on either side of the double bond must be attatched to 2 different groups and at least one of those groups must be the same on either side

E/Z isomers

Element/ molecule with highest atomic number is given priority

Alkane general formula

CnH2n+2

Alkane reactivity

Non-polar, insoluble in water and unreactive

Sigma bond

Form when electron orbitals from adjacent atoms directly overlap, contains 2 electrons, fully rotational

Intermolecular forces in Alkanes

Van der waals, weak therefore low bp for short chain alkanes and bp increases as carbon number increases

Boiling point for branched alkanes vs linear alkanes

Branched chain alkanes have lower boiling points as van der waal forces work better over shorter distances

Benefits of cracking

Converts long chain hydrocarbons to short chain hydrocarbons

produces alkenes which are highly reactive and useful molecules

Thermal cracking

high temperature 450ºC-900ºC

high pressure 70atm

forms alkanes and alkenes

high yield of alkenes

Catalytic cracking

High temperature 450ºC

Low pressure 1-2 atm

zeolite catalyst

branched chain alkanes, cycloalkanes and aromatic hydrocarbons are produced

Alkene general formula

CnH2n

Shape/ Bond angle of Alkene

planar molecule, 120º

pi bonding

p orbitals above and below the sigma bond overlap sideways to form a pi bond, area of high electron density

can pi bonds rotate

no

which has a higher bond enthalpy sigma or pi bonds

sigma

Markovnikoff’s rule

Markovnikoff's rule states that in the addition of a Hydrogen Halide to an asymmetric alkene, the hydrogen atom of the acid bonds to the carbon atom that already has the greater number of hydrogen atoms, while the halogen atom bonds to the carbon atom that has fewer hydrogen atoms.

Are halogenoalkanes soluble in water?

No, C-H bonds are non polar and are not compensated for enough by C-X bond polarity

Do Halegenoalkanes have a polar bond and why?

Yes, hydrogen and halogens have large electronegativity difference

What would increase bp of Halogenoalkane?

Increase carbon chain length, halogen further down group 7

How does reactivity of halogenoalkanes change down the group?

Increases as bond enthalpy of C-X bond decreases

What is a nucleophile?

An electron donor (negative ion)

3 Examples of nucleophiles (first element has lone electrons)

OH-

CN-

NH3

What is nucleophilic substitution?

Nucleophile donates a lone pair of electrons to a C atom and a partially negative atom leaves the molecule

What are CFCs?

Chloro-Floro-carbons

What is the problem with CFCs?

Normally unreactive, they can catalyse the breakdown of ozone via free radical substitution

What are CFCs being replaced with?

HCFCs

HFCs

What are the conditions / reactants needed for the elimination reaction of halagenoalkanes?

NaOH/ KOH

ethanolic conditions

heated

What is formed in the elimination reaction of halogenoalkanes?

An alkene, water and a halogen ion

What isomers can alkenes form?

Chain isomers

Position isomers

Geometric E-Z isomers

What is an electrophile?

Electron deficient ions/ atoms which accept a pair of electrons

what is the most stable kind of carbocation intermediate? why?

alkyl group have a positive inductive effect so the most stable is a tertiary carbocation

What conditions are needed for the electrophilic addition of H2O to an alkene?

Acid catalyst, usually phosphoric acid

What conditions are needed for the electrophilic addition of a hydrogen halide to an alkene?

room temperature

What conditions are needed for the electrophilic addition of a halogen molecule to an alkene?

Room temperature and organic solvent

What is an addition polymer?

Many monomers bonded together without the loss of any atom or molecule

3 uses of PVC

drain pipes

vinyl

aprons

2 plasticisers

esters and pthalates

what are plasticisers?

small molecules that get between polymer chains to force them apart and allow them to slide over one another

how do the physical properties of PVC change due to a plasticiser? what applications does this lead to?

becomes more flexible- used for aprons

What is mechanical recycling?

Where plastics are separated into different types, washed, ground down, melted and remoulded

What is feedstock recycling?

Plastics heated to a temperature which break polymer bonds, leaving original monomers that can be made into new plastics

Do alcohols have hydrogen bonding?

yes as there is an O-H bond

How can ethanol be made from crude oil?

Hydration of ethene via electrophilic addition (phosphoric acid catalyst)

How can ethanol be made by fermentation?

Plant carbohydrates broken down and fermented by enzymes in yeast → ethanol

What conditions are needed for fermentation?

Enzymes in yeast as catalyst, 35ºC, anaerobic conditions

Equation for fermentation of glucose?

C6H12O6 → 2C2H5OH + 2CO2

In the future, how might most ethene be made? why is it not made like this at the moment?

dehydrate ethanol made by fermentation → ethene

not economical at the moment

Definition of carbon neutral

No net addition of CO2 to the atmosphere all CO2 released is taken back in

Conditions for elimination alcohols to alkenes

Excess hot concentrated sulphuric acid or pass vapour over hot aluminium oxide

What is formed from a partially oxidised primary alcohol?

An aldehyde

Conditions to form an aldehyde

dilute sulphuric acid, potassium dichromate (VI), distill product as it’s produced, gentle heating

Write an equation for the partial oxidation of ethanol

CH3CH2OH + [O] → CH3CHO + H2O

Fully oxidised primary alcohol

Carboxylic acid

conditions to fully oxidise a primary alcohol to a carboxylic acid

concentrated sulphuric acid, potassium dichromate (VI), reflux and strong heating

Write an equation for the full oxidation of ethanol

CH3CH2OH + 2[O] → CH3COOH + H2O

What forms if you oxidise a secondary alcohol?

a ketone

why can a secondary alcohol not be oxidised further and why can’t a tertiary alcohol be oxidised?

a carbon carbon bond would have to break

what conditions are needed for the oxidation of a secondary alcohol?

concentrated sulphuric acid, potassium dichromate (VI), reflux and strong heating (ketone)

What is an aldehyde?

Molecule with C=O group at the end of a carbon chain

What is a ketone?

Molecule with C=O group in the middle of a carbon chain

What is a carboxylic acid?

Molecule with a COOH group, which has to be at the end of the carbon chain

Tollens’ tests for?

aldehydes

What is in Tollens’ reagent? How does this react with the substance to be tested?

Silver nitrate in NH3 - oxidises aldehydes but not ketones, complex silver ions reduced to solid

What is Fehling’s testing for?

Aldehydes

What is in Fehling’s? How does this react with the substance to be tested?

Blue copper (II) complex ions - gentle oxidising agent

reduced to Cu 2+ ions

needs heat

How are esters formed?

Carboxylic acid + alcohol in presence of an acid catalyst

How are esters named?

Alcohol → alkyl

carboxylic acid → carboxylate

alkene → polyalkene

high pressure

catalyst

alkene → dihalegnoalkane

Br2/cl2 at room temp

Electrophilic addition

Alkene → alcohol

H2SO4

Electrophilic addition

H2O warmed

hydrolysis

alkene → halogenoalkane

HBr/HCl room temp

Electrophilic addition

dihalegenoalkane → diol

KOH aqueous

heat under reflux

Nucleophilic substitution

Alkane → halegenoalkane

Br2 / Cl2

UV light

Free radical substitution

alcohol → alkene

concentrated H2SO4

Elimination

dehydration

halegenoalkane → alkene

KOH alcoholic

heat under reflux

elimination

halegenoalkane → alcohol

KOH aqueous

heat under reflux

Nucleophilic substitution

halogenoalkane → nitrile

KCN in ethanol / water mixture

heat under reflux

Nucleophilic substitution

halogenoalkane → 1º amine

Alcoholic NH3

heat under pressure

Nucleophilic Substitution

1º amine → 2º amide

acyl chloride

room temperature

nucleophilic addition elimination

1º amine → 2º amine, 3º amine, Quaternary salt

halogenoalkane

nucleophilic substitution

Acyl chloride/ acid anhydride → secondary amide

1º amine

room temp

nucleophilic addition elimination

acyl chloride/ acid anhydride → primary amide

NH3 room temp

Nucleophilic addition elimination

acyl chloride / acid anhydride → ester

alcohol

room temp

nucleophilic addition elimination

acyl chloride / acid anhydride → carboxylic acid

H2O

room temp

nucleophilic addition elimination

carboxylic acid → ester

alcohol + H2SO4

heat

esterification

alcohol → ester

Carboxylic acid + H2SO4

heat

esterification

aldehyde → carboxylic acid

Na2Cr2O7/ H+

heat under reflux

oxidation

aldehyde → hydroxynitrile

NaCN + H2SO4

Nucleophilic addition

Ketone → hydroxynitrile

NaCN + H2SO4

Nucleophilic addition

ketone → alcohol

NaBH4

reduction

nucleophilic addition

aldehyde → alcohol

NaBH4

reduction

nucleophilic addition

alcohol → aldehyde

1º alcohol

Na2Cr2O7 / H+

heat and distil

partial oxidation