Benzenes Flashcards
Alcohol → Alkene
Reagents
Conditions
Type of reaction
- Conc H2SO4
- Reflux at 180°C
- Dehydration
Alkene→Alcohol
- H3PO4
- steam, 60/70 atm & 300°C
- Hydration
1° Alcohol→Aldehyde
- Acidified potassium dichromate
* Distill off as it forms
2° Alcohol→Ketone
• Acidified Potassium Dichromate
Halogenoalkane → Alcohol
- Aqueous NaOH
- Reflux
- Nucleophilic Substitution
Carboxylic Acid → Alcohol
- LiAlH4
* Dry ether
Ketone → Secondary Alcohol
- NaBH4
- Dry ether
- Secondary Alcohol
Carboxylic Acid → Alkane
- NaOH
- Heat
- Na2CO3
- Decarboxylation
Benzene → Nitrobenzene
- Conc HNO3 and Conc H2SO4
- reflux at 50°
- Nitration
Ethanoyl Chloride → Carboxylic Acid
- Water
- Room temp
- Steamy fumes of HCl
- Hydrolysis
Ethanoyl Chloride → Ester
- CH3OH
* Ester & HCl
Benzene → Methylbenzene
Reagents
Catalyst
Reaction type
- CH3Cl
- AlCl3
- Electrophilic Substitution
Structure of Benzene
∙Formula C₆H₆
• Each C is bonded to 2C’s and 1H covalently
∙Trigonal planar with bond angle of 120°
• Sideways overlap of p orbitals
∙Delocalised structure of benzene has π cloud of electrons
∙All bond lengths are the same
Benzene → Bromobenzene
Reagents
Catalyst
- Br2
* FeBr3
What type of reaction is Alcohol → Carboxylic Acid?
Oxidation
What type of reaction is Carboxylic Acid → Alcohol?
Reduction
What type of reaction is Halogenoalkane→Alcohol?
Nucleophilic substitution
What type of reaction is Alcohol→Ketone?
Oxidation
What type of reaction is Ketone→Alcohol?
Reduction
What type of reaction is Halogenoalkane→Alkene?
Elimination
What type of reaction is the Nitration of Benzene?
Electrophilic Substitution
What type of reaction is the Alkylation of Benzene? (Benzene→Methylbenzene)
Electrophilic Substitution
What test will show the presence of a CH₃C=O bond or a CH₃CH(OH) bond?
The Iodoform Tests
What does 2,4-DNPH test positive for?
A carbonyl group
What does Tollen’s reagant test for?
Aldehyde
What colour change occurs when K₂Cr₂O₇/H⁺ acts as a oxidising agent?
Orange to Green
In order of acidity from weakest to strongest, arrange these compounds- Ethanol, Phenol, Water, Ethanoic acid?
Ethanol, Water, Phenol, Ethanoic acid
What does ‘heating under reflux’ mean?
Evaporation and Condensation of a material in which the condensed material returns to the flask
Methylbenzene→Benzoic acid
KMnO₄ acidified with dil HCl
1° Alcohol → Carboxylic Acid
Reagents
• Acidified Potassium Dichromate
What is the positive test observation for Iodoform
- Pale yellow precipitate
* CHI3
What is the positive test observation for Tollen’s reagent
• Silver Mirror
What does Fehling’s Solution test positive for?
An aliphatic aldehyde
What is the positive test observation for Fehling’s Solution?
The blue solution forms a red precipitate
Ester → Carboxylic Acid
Reagent
Condition
Product
- dil HCl / Naoh
- Room temp / Heated under reflux
- Cooh acid & alcohol
Carboxylic Acid → Ester
Reagents
Conditions
Product
- Alcohol & Conc H2SO4
- Heat
- Ester and Water
Ester → Carboxylic Salt + Alcohol Reagents Conditions Product Reaction type
- NaOH solution
- Heated under reflux
- Cooh Salt & alcohol
Aldehyde → Carboxylic Acid
Reagents
Conditions
- Acidified Potassium Dichromate
* Heat & reflux & excess of [o]
Why does propan-1-ol have a greater solubility in water than pentan-1-ol?
The contribution of the OH group in pentan-1-ol is much less than in propan-1-ol because of the larger non-polar group in pentan-1-ol
Phenol → Phenyl ethanoate
Reagents
Conditions
Products
- Ethanoyl Chloride
- Room temp
- Phenyl ethanoate & HCl
Alcohol → Halogenoalkane Formation of HBr Reagents Conditions Products
• KBr & conc H2SO4
- HBr
- reflux
- Halogenoalkane & water
Ways to form an Alcohol
- Nucleophilic Substitution of Halogenoalkane
- Amine with Nitrous acid
- Alkenes
- Reduction of Carbonyls
- Hydrolysis of Ester
Carboxylic Acid → Alcohol
Reagents
Conditions
• LiAlH4
• Excess of reducing agent
Halogenation of Benzene
Reagents
Conditions
Products
- Cl/Br
- Absence of light, room temp, anhydrous conditions & halogen carrier
- C6H5Cl/Br & HCl
Explain why it is difficult to react Chlorobenzene with sodium hydroxide
The chlorine line pairs interact with the ring electrons which strengthens the C-Cl bond by decreasing bond polarity. This makes chlorobenzene less susceptible to nucleophilic attack.
Alkylation of Benzene
Reagents
Conditions
- CH3Cl & AlCl3
* room temp & Dry inert solvent
Alcohol → Aldehyde
Reagents
Conditions
Reaction type
- Acidified Potassium Dichromate
- Heat, excess alcohol & remove aldehyde as it forms
- Oxidation
Alcohol → Alkene
Reagents
Products
- Al2O3 powder
* Ethene, water vapour
Explain why phenol is more acidic than a primary alcohol.
The phenoxide ion is stabilised by charge delocalisation and the alkyl groups would not delocalise ion.
The mechanism for the reaction between ethanal and hydrogen cyanide is shown below. Describe what is happening at each stage of this reaction mechanism and use your answer to explain why this reaction is described as nucleophilic addition.
Hydrogen cyanide dissociates giving a H+ and cyanide ion. The mechanism is described as nucleophilic addition because the cyanide ion acts as a nucleophile. Electron density increases and produces a negative charge on the oxygen atom. The oxygen acts as an electron pair donor, attacking a hydrogen ion. In effect, the HCN has added across the C=O.
Explain what is meant by the delocalisation energy of benzene
The extra stability in the benzene molecule due to electron delocalisation.
What does electrophilic addition involve
A C=C
What does electrophilic substitution involve
A benzene ring
What does nucleophilic substitution involve
A halogenoalkane and CN-, OH-, or NH3
What does nucleophilic addition involve?
An aldehyde or a ketone
Why is there such a low percentage yield when benzene is converted to benzoic acid?
There is a two step process which means losses can occur at both stages and oxidation may not be completed, forming some aldehydes.
