Module 6 phenols + benzene

what is the molecular formula benzene

C₆H₆

what is the bond angle and shape of carbons in benzene

120°C

trigonal planar

what type of molecule is benzene ?

Cyclic

what is the general formula of benzene

CₙHₙ

what forms the delocalised π ring in benzene

the fourth e⁻ is delocalised

the lone e⁻ in the p-orbital overlap to form a delocalised ring of electrons

what are the two structures/ models of benzene

Kekule model

the delocalised model

which experimental data proves that kekule model is incorrect

C-C bonds are the same length / in kekules bonds would have different lengths and strengths because of the C=c bonds

Benzene is unreactive and doesn't undergo addition reactions readily

∆H Hydrogenation is about 152 kjmol⁻1 less then expected

why is benzene unreactive?

due to the delocalised ring of π 6 electrons in 6 p-orbitals

hard to break the π ring

another name for kekule structure

triene

how do we know benzene doesn't contain C=C

Bromine water doesn't react with benzene

no visible change

what is the bonding in benzene

Carbons have 3 covalent bonds

spare lone electron in the p-orbital overlap to form delocalised π ring

What are arenes/aromatic compounds?

molecules containing a benzene ring

how to name benzene

when benzene is the main functional group ( C₆H₆) --> the suffix is benzene

when benzene isn't main functional group, the molecule is named as a phenyl group - prefix

the suffix comes from other molecule

naming benzene ( image)

Give functional group lowest number

what is a phenyl group molecule formula

C₆H₅

similarities between kekule and delocalised structure of benzene

both have p-orbitals overlapping sideways

π bond above and below plane of carbon atoms

Phenol image

molecular formula of Phenol

C₆H₅OH

what are the reactions benzene undergoes

Nitration

Halogenation

Acylation

Alkylation

what is the only type of reaction benzene undergoes

Electrophilic substitution

what is the overall equation for the nitration of Benzene

C₆H₆ + HNO₃ → C₆H₅NO₂ + H₂O

catalyst in the nitration of benzene

Concentrated H₂SO₄

why is the catalyst in nitration of benzene the catalyst

H₂SO₄ is reformed during the reaction

effects of using higher temperatures in the nitration of benzene

Forms Poly nitro benzenes instead of mono

how to form nitro benzene

React benzene with Nitric acid ( HNO₃)

what are the 3 steps in electrophilic substitution reactions

Step 1 —> forming the electrophile

Step 2 —> electrophile attack ( Mechanism)

Step 3 —> reforming the catalysts

equation for forming the nitronium ion

HNO₃ + H₂SO → NO₂⁺ + HSO₄⁻ + H₂O

Electrophilic substitution ( Nitration) mechanism

Equation to reform the catalyst in the nitration of benzene

HSO₄ + H⁺ → H₂SO₄

H⁺ comes from the mechanism

what is the nitration of benzene

benzene + Nitric acid

general equation for the Halogenation of benzene

C₆H₆ + X₂ → C₆H₅X + HX

X= Cl / Br

what are the catalysts for the halogenation of benzene

Halogen carriers

what are the halogen carriers

aluminum chloride (AlCl₃)

Iron bromide (FeBr₃)

what is the electrophile in the Nitration of benzene

NO₂⁺

what is the electrophile in the halogenation of benzene

Cl⁺/Br⁺

equations for making the electrophile in the halogenation of Benzene

AlCl₃ + Cl₂ → AlCl₄⁻ + Cl⁺

how is the electrophile formed in the halogenation of benzene

Halogen carrier reacts with the halogen forming a halogen carrier ( 4 halogens ) anion and a halogen cation

Electrophilic substitution ( Halogenation) mechanism

Equations to reform catalyst halogenation of benzene

AlCl₄⁻ + H⁺ → AlCl₃ + HCL

Why do we use halogen carriers for Benzene and not alkenes

Benzene has a delocalised π bond ring makes it too stable

Alkenes has a localised π bond which is less stable

what is always carbon - 1 in a phenol

Carbon attached to Hydroxyl group

what is the suffix of all phenols

phenol

What is the PH of phenols

slightly acidic

word equation for Phenol + sodium hydroxide

Phenol + sodium hydroxide —> sodium phenoxide + water

displayed equation for phenol + sodium hydroxide

dont show ionic bond C⁺ attracts to anion

why dont phenols react with Na₂CO₃

sodium carbonate isn’t a strong enough base

Cant remove the H⁺ from the O₂ atom

what are electron donating groups ( EDG)

increase the electron density of Carbon 2,4,6

makes them more susceptible to electrophilic attacks

Examples of EDG

NH₂ ( amino group)

OH ( Hydroxyl group)

Why are phenols more susceptible to electrophiles then benzene

Higher electron density

due to the lone electron pair in the p orbital of the Oxygen atom overlaps with the delocalised π ring

what is Electron withdrawing group ( EWG)

Decrease electron density from the ring

re directs the electrophile to carbon 5,3

example of a EWG and features

NO₂

no orbitals that can overlap with the delocalised ring

electronegative

why do phenols react with Br₂ when benzene doesn't

higher electron density

what are the Friedel-Crafts reactiosn

Acylation

Alkylation 

what are the conditions for Friedel-Crafts reactions 

Heat under reflux

Halogen carrier catalyst

acyl group ( image)

Acyl group + Benzene =

Phenyl ketone + HCL

Products of Acylation of benzene

Role of halogen carrier in Friedel-Crafts reactions

Halogen carrier strengths the electrophile ( making a carbocation) → increases polarity

Generating electrophile in Acylation equation 

R-COCL + AlCl₃ → RC⁺O + AlCl₄⁻

what type of electrophile is acyl chloride

Weak electrophile 

Acylation of benzene mechanism ( Image)

effects of halogen carrier in Friedel Crafts

generates Carbocation

Removes and steals halogen from alky/ Acyl 

General equation for Alkylation reaction

R - X + Benzene → Phenyl alkane + HX

Forming the electrophiles in Alkylation equation

R-X + AlCl₃ → R⁺ + AlCl₄⁻

Friedel crafts mechanism explanation

Carbocation accepts lone pair e⁻ from the benzene

makes benzene partial and positive

Halogen anion Cl breaks to join hydrogen to HCl

Forms phenyl ketone