Module 6: Aromatic Chem Flashcards by Shona Mallen

Structure of benzene
What is benzene’s formula

C6H6

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Structure of benzene
What is benzene basic structure

Six C atoms in a hexagonal ring with onto H atom bonded to each carbon atom
Molecule is planar

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Structure of benzene
What is true to length of all bonds in benzene

All same length-intermediate between single and double bonds

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Structure of benzene
How many sigma bonds does each C atom make with what

3 sigma bonds, 2 with C atoms, one with H atom

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Structure of benzene
Where is the 4th unused electron on each C atom

In a p orbital perpendicular to plane of ring

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Structure of benzene
What happens to the p orbital with unused electron

Overlaps with neighbouring p orbital forming a pi Bond

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Structure of benzene
What is the overall result of pi bonds

Ring of negative charge above and below plane of the ring

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Structure of benzene
What does the electrons in the pi system being delocalised mean

Do not belong to any particular C atom or bond and are free to move throughout whole pi system

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Structure of benzene
Why is benzene molecule more stable

Electrons are delocalised and more spread out and will repel each other less

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Structure of benzene
What is the electron density of the pi system

Low

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Structure of benzene
What are the labels on a detailed benzene diagram

P orbitals
Sigma bonds
Pi bonds, electrons from p orbitals delocalise above and below the carbon ring =lower electron density

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Structure of benzene
What are the bonding angles of benzene

120

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Kekulés structure
What structure did kekule suggest

Six carbon ring joined by alternate single and double bonds

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Kekulés structure
How many sigma bonds in keklule structure

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Kekulés structure
Labels on kekule diagram

P orbitals
Sigma bonds
Pi bonds, sideways overlap of p orbitals= localised electrons between 2 carbon atoms = high electron density

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Disproving kekulè model
3 pieces of evidence

C-C bond lengths
Addition reactions
Enthalpy of hydrogenation

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Disproving kekulè model
Explain c-c bond length

All c-c bonds are same length in benzene between length of sing and double carbon bonds
If benzene was triene would expect three longer c-c single and three shorter c=c double

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Disproving kekulè model
Explain addition reactions

Benzene does not readily undergo addition reactions (eg doesn’t decolourise bromine water)
If benzene was triene would expect it to ready undergo addition

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Disproving kekulè model
Explain enthalpy of hydrogenation using numbers

Would expect triene to react with 3 H2 to form cyclohexane releasing 360 kj/mol of energy
Benzene only releases 208 kj/mol of energy showing benzene 152 kj/mol more stable
Extra stability due to delocalisation of electrons

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Naming aromatics compounds
What groups are shown as prefixes to benzene

Alkyl groups, halogens and nitro groups

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Naming aromatics compounds
Name with a C2H5 group monosubstutudted

Ethylbenzene

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Naming aromatics compounds
Name with Cl monosubstituted

Chlorobenzene

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Naming aromatics compounds
Name with NO2 monosubstituted

Nitrobenzene

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Naming aromatics compounds
When does the benzene ring become the substituent

When ring is attached to alkyl group with functional group or alkyl chain with more than 7 carbon atoms

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Naming aromatics compounds What is the prefix when benzene ring is a substituent

Phenyl

Naming aromatics compounds What are the three common exceptions just learn

Benzoic acid or benzenecarboxylic acid Phenylamine (NH2 group ) Benzaldehyde (benzenecarbaldehyde)

Naming aromatics compounds What happens when more than one substituent groups

Ring numbered like normal and use di, tri etc

Benzene reactions What kind of reaction does benzene undergo

Electrophilic substitution

Benzene reactions Why does benzene undergo electrophilic substitution

Electrons are in ring with lower electron density

Benzene reactions Why can’t benzene undergo addition

Can’t induce a dipole

Benzene reactions What are the three types of reactions benzene can undergo

Nitration Halogenation Friedal-crafts reactions

Nitration of benzene What is the overall reaction

Benzene + HNO3 —> Nitrobenzene + H2O

Nitration of benzene What are the conditions

Conc HNO3 Conc H2SO4 50’C

Nitration of benzene Why are the conditions needed

As benzene cannot generate electrophiles so has to be given

Nitration of benzene What is step 1 called

Generating electrophile

Nitration of benzene What is the equation for generating the electrophile

HNO3 + H2SO4 —> NO2^+ + HSO4^- + H2O

Nitration of benzene What is the electrophile and what is it called

NO2^+ Nitronium ion

Nitration of benzene What acts as a catalyst

H2SO4

Nitration of benzene What is step 2 called

Electrophilic substitution

Nitration of benzene What is step 2

The reaction mechanism LEARN

Nitration of benzene What is created at the end of step 2

Nitrobenzene and a H+ ion

Nitration of benzene What is step 3 called

Regeneration of catalyst

Nitration of benzene Equation for regeneration of catalyst

H^+ + HSO4^- —> H2SO4

Halogenation of benzene What is the overall equation

Benzene + halogen —> halobenzene + hydrogen halide

Halogenation of benzene Conditions for chlorine

AlCl3 Cl2 50’C

Halogenation of benzene Equation to generate electrophile using chlorine

AlCl3 + Cl2 —> Cl^+ + AlCl4^-

Halogenation of benzene What is AlCl3

Halogen carrier

Halogenation of benzene What is the electrophile

Cl^+

Halogenation of benzene What is the catalyst

AlCl3

Halogenation of benzene What is the mechanism

LEARN

Halogenation of benzene What are the the product of mechanism for chlorine

Chlorobenzene + H^+ ion

Halogenation of benzene Regeneration of catalyst with Cl

AlCl4^- + H^+ —> HCl + AlCl3

Halogenation of benzene Generation of electrophile using Br

FeBr3 + Br2 —> Br^+ + FeBr4^-

Halogenation of benzene What is the electrp[hile when br

Br^+

Halogenation of benzene What is FeBr3

Halogen carrier and catalyst

Halogenation of benzene Products of mechanisms using br

Bromobenzene + H^+

Halogenation of benzene Regeneration of catalyst using br equation

FeBr4^- + H^+ —>HBr + FeBr3

Friedal-crafts reactions What are they useful for

Synthesis as is a way of adding C atoms onto an aromatic ring

Friedal-crafts reactions What are the two types

Alkylation Acylation

Friedal-crafts reactions alkylation Overall reaction using Cl

Benzene + ClCH3 —AlCl3–> methyl benzene + HCl

Friedal-crafts reactions alkylation Conditions

Halogen carrier Haloalkyl Ether (dry solvent) Room temp

Friedal-crafts reactions alkylation What is the catalyst

Halogen carrier

Friedal-crafts reactions alkylation Equation to generate electrophile

CH3Cl + AlCl3 —> AlCl4^- + CH3^+

Friedal-crafts reactions alkylation What is the electrophile

CH3^+

Friedal-crafts reactions alkylation What is the mechanism

LEARN

Friedal-crafts reactions alkylation What two products are produced in the mechanism

Methylbenzene + H^+

Friedal-crafts reactions alkylation Equation for regeneration of catalyst

H^+ + AlCl4^- —> HCl + AlCl3

Friedal-crafts reactions acylation What is an acyl group

Contains C=O double bond

Friedal-crafts reactions acylation What is produced when with an acyl chloride

Phenylketone or benzaldehyde

Friedal-crafts reactions acylation Overall equation

Benzene + acyl chloride —AlCl3-> phenylketone/benzaldehyde + HCl

Friedal-crafts reactions acylation Conditions

Halogen carrier Reflux at 50’C Acyl chloride Ether(dry solvent)

Purification of an organic solid How can they be purified

Recrystallisation

Purification of an organic solid Basic concept of recrystallisation

Dissolve solid in a solvent to make e a saturated solution and let cool As cools solubility of product falls and forms crystallises

Purification of an organic solid Steps in purification

1. Very hot solvent added to impure solid until it just dissolves, don’t add too much 2. Should give a saturated solution of impure product 3. Solution left to cool slowly over ice , crystals of product form as it cools, impurities stay in solution, present in smaller amounts then product so takes much longer to crystallised 4. Crystals removed by filtration under reduced pressure and washed with ice cold solvent 5. Dried on watch glass leaving purer organic solid

Purification of an organic solid What does the solvent have to do to be appropriate

Only work if solid very soluble in hot solvent but Nearly insoluble when solvent cold

Purification of an organic solid What would happen if product not soluble enough in hot solvent

Won’t be able to dissolve it all all

Purification of an organic solid What will happen if product too soluble in cold solvent

Most of it will stay in solution even after cooling and when filter will lose product giving low yield

Purification of an organic solid What os used when filtering under reduced pressure

Büchner funnel with damp filter paper

Purification of an organic solid How is Buchner funnel set up

With damp filter paper and sealed side arm (hersh) flask connected to a vacuum line causing it to be under reduced pressure

Purification of an organic solid Labels needed on diagram of Büchner funnel

Pump Hirch flask Filter paper Büchner funnel Vacuum pump

Purification of an organic solid What does the reduced pressure do

Causes suction through the funnel which causes liquid to pass quickly into the flask leaving dry crystals of product

Purification of an organic solid What is done to check purity

Melting and boiling point checked as pure substances have very specific ones

Purification of an organic solid What happens to melting and boiling points ig impure

Melting point lowered and boiling point raised

Purification of an organic solid How is melting point accurately measured

Small amount put in capillary tube and tube gently tapped to get solid to fall to bottom Tube placed in beaker of oil with sensitive thermometer Slowly heated with constant stirring until solid just melted and read thermometer

Purification of an organic solid What do you do with measured melting point to check purity

Compare to known melting point of substances

Phenol What are phenols

Benzene rings with -OH group attached

Phenol What is the formula

C6H5OH

Phenol How do you name phenols with other groups substituted

Number carbons starting from the one with the -OH group

Phenol What mechanism does phenol undergo

Electrophilic substitution

Phenol Is phenol more or less likely to undergo electrophilic substitution then benzene

More likely

Phenol Why does phenols more readily undergo electrophilic substitution

One of lone pairs of electrons in p orbital of oxygen atoms overlaps with the delocalised ring of electrons in the benzene ring so partially delocalised into the pi system This increases electron density of ring so is more likely to be attacked by electrophiles

Phenol What does this mean for reactions

Don’t require catalyst

Phenol What is phenol standard state

Almost colourless crystalline solid

Phenol What is phenol standard state

Almost colourless crystalline solid

Phenol Is phenol soluble

Yes

Phenol Why is it soluble

Can form hydrogen bonds

Reactions of phenol What does it produce in complete combustion

CO2 + H2O

Reactions of phenol Equation for complete combustion

C6H5OH + 7O2 —>6CO2 + 3H2O

Reactions of phenol What is observed for combustion

Sooty flame

Reactions of phenol Why is a sporty flame the observation for combustion

Incomplete combustion more likely due to high % of carbon

Reactions of phenol How can you test from phenol from benzene

Reaction with bromine water

Reactions of phenol What is observed from phenol and bromine water

Decolourises br2 White ppt

Reactions of phenol How is bromine used to test phenol from benzene

Phenol is more reactive so decolourises bromine but benzene does not

Reactions of phenol What is produced when reacted with bromine

2,4,6-tribromophenol

Reactions of phenol What can u smell when reacted with bromine

Antiseptic

Reactions of phenol What is the equation for phenol and bromine

Phenol + 3Br2 —> 2,4,6-tribromophenol + 3HBr

Reactions of phenol Equation for chlorine and phenol

Phenol + 3Cl2 —> 2,4,6-trichlorophenol + 3HCl

Reactions of phenol What is produced in nitration of phenol

Two isomers of nitrophenol and water

Reactions of phenol What two isomers are produced in nitration of phenol

2-nitrophenol 4-nitrophenol

Reactions of phenol What colour does phenol go in universal indicator

Orange

Reactions of phenol What ph does phenol have and what does this mean

3/4 Is a weak acids

Reactions of phenol What does phenol dissociate to form

Phenoxide ion and hydrogen ion

Reactions of phenol Equation four dissociation of phenol

Phenol <==> phenoxide ion + H+

Reactions of phenol What type fo reaction is phenol and sodium hydroxide

Neutralisation

Reactions of phenol Equation for phenol and sodium hydroxide

Phenol + NaOH —> C6H5O- Na+ + H2O

Reactions of phenol Does phenol react with sodium carbonate

Reactions of phenol Why doesn’t phenol react with Na2CO3

Not strong enough acid top displace O2

Reactions of phenol Why is phenol and acid

Partially delocalised electron and dipole in O-H bond so bond is weaker and easier to donate proton, H+

Reactions of phenol Equation for phenol with sodium

2Phenol + 2Na —> 2C6H5O- Na+ + H2(g)

Reactions of phenol What type of reaction is sodium and phenol

Redox

Reactions of phenol What is the salt produced on sodium and phenol called

Sodium phenoxide

Reactions of phenol distinguishing acid How does C6H5OH react with Na and CO3 2-

Effervescence from H2(g) with Na No reaction with CO3 2-

Reactions of phenol distinguishing acid How does C4H9OH react with Na and CO3 2-

No reaction with either

Reactions of phenol distinguishing acid How does C4H9COOH react with Na and CO3 2-

Effervescence with both

Reactions of phenol distinguishing acid Strength is order for C6H5OH, C4H9OH, C4H9COOH

C4H9COOH strongest then C6H5OH then C4H9OH

Reactions of phenol distinguishing acid Dissociation of C4H9COOH

—> C4H9COO- + H+

Reactions of phenol distinguishing acid Why is C4H9COOHthe strongest

Pulls electrons away

Reactions of phenol distinguishing acid Dissociation of C6H5OH

<==> C6H5O- + H+

Reactions of phenol distinguishing acid Dissociation of C4H9OH

Doesn’t

directing groups when does directing effects happen

substitution of second groups on a benzene ring

directing groups what are directing groups

1st group directs positions of second substituted groups

directing groups why does the directing effect happen on substituted benzene rings

functional group can change electron density at certain carbon atoms making them more or less likely to react

directing groups what are the two types of directing groups

2- and 4-directing groups 3- directing groups

directing groups what types of groups are 2- 4- directing groups

activating groups electron donating groups

directing groups why are electron donating groups 2- 4- directing

have electrons in orbitals that overlap with delocalised ring and increase its electron density in particular at carbons 2 4 and 6 so most likely to react at those postions

directing groups what are two most common 2- 4- directing groups

-OH -NH2

directing groups possible positons names for electron donating groups

2- 2,4-di 4- 2,6-di

directing groups what types of groups are 3- directing groups

deactivating groups electron withdrawing groups

directing groups why are electron with drawing groups 3- directing

don't have electrons in orbitals that are overlapping with the delocalised ring and is electronegative so withdraws electron density particularly withdrawing at carbons 2- 4- 6- unlikely to react here and has effect of direction electrophilic subsitittion at 3- 5- psotuons

directing groups what is common 3- directing group

-NO2

directing groups possible position names for electron withdrawing groups

3- 3,5-di

Module 6: Aromatic Chem Flashcards

(143 cards)