Chemistry Bond Cleavage Types

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Questions and Answers

What is placed in a 2-l round-bottomed flask?

390 g of aniline hydrochloride and 190 g of urea

250 g of pinacol hydrate and 750 g of 6 N sulfuric acid (correct)

750 g of pinacol hydrate

750 g of 6 N sulfuric acid and 250 g of urea

How many moles of pinacol hydrate is used in the process?

5.42 moles

2.42 moles

4.42 moles (correct)

3.2 moles

What is the boiling point range of the pinacolone?

120–125°C

110–115°C

103–107°C (correct)

95–100°C

What is added to the water after the first distillation?

Concentrated sulfuric acid and pinacol hydrate Signup and view all the answers

What is the yield of pinacolone from one run of the process?

287–318 g Signup and view all the answers

What is the purpose of redistillation of the pinacolone?

To remove the yellow color Signup and view all the answers

What is the ratio of aniline hydrochloride to urea in the solution?

3:3.2 Signup and view all the answers

How is the carbanilide washed?

With 100 cc of boiling water Signup and view all the answers

What is the type of bond cleavage where the shared pair of electrons remains with one of the fragments?

Heterolytic cleavage Signup and view all the answers

What is the term for the energy required to cleave a chemical bond?

Bond dissociation energy Signup and view all the answers

What is the term for the species that donate a proton?

Acids Signup and view all the answers

What type of bond cleavage produces electrically neutral fragments called free radicals?

Hemolytic cleavage Signup and view all the answers

What is the term for the process where the bond breaks in such a way that the shared pair of electrons is divided equally between the products?

Electronically symmetrical bond cleavage Signup and view all the answers

What is the term for the species that accept a proton?

Bases Signup and view all the answers

What type of bond cleavage requires the bond to be polarized, leading to the separation of oppositely charged ions?

Heterolytic cleavage Signup and view all the answers

What is the example of a molecule that undergoes hemolytic cleavage?

Benzoyl peroxide Signup and view all the answers

What is the temperature range of the ligroin used in the purification process?

90-100°C Signup and view all the answers

What is the melting point of the purified benzopinacol?

188-190°C Signup and view all the answers

What is the percentage yield of benzipinacol in the first reduction?

93-94% Signup and view all the answers

What is the name of the reaction that involves the coupling of 2 aryl halides in the presence of sodium metal in dry ethereal solution?

Fittig reaction Signup and view all the answers

What is the role of acid in the pinacol-pnacolone rearrangement?

It provides the necessary conditions for the rearrangement to take place Signup and view all the answers

What is the result of the removal of a water molecule in the first step of the pinacol-pnacolone rearrangement mechanism?

Formation of a carbocation Signup and view all the answers

What is the product of the pinacol-pnacolone rearrangement?

A carbonyl compound Signup and view all the answers

How many portions of benzophenone can be reduced using this procedure?

6-7 Signup and view all the answers

What is the difference between basicity and nucleophilicity?

Basicity is concerned with donation of lone pairs to hydrogen, while nucleophilicity is concerned with donation of lone pairs to all other atoms. Signup and view all the answers

What is the trend in nucleophilicity as electron density increases?

Nucleophilicity increases as electron density increases. Signup and view all the answers

What is the role of solvent in nucleophilicity?

Solvent is one of the key factors that contribute to nucleophilicity. Signup and view all the answers

What is the relationship between the conjugate base and nucleophilicity?

The conjugate base is a better nucleophile. Signup and view all the answers

What is the PKa of hydroxide ion?

15.7 Signup and view all the answers

What is the difference between hydroxide ion and cyanide ion?

Hydroxide ion is a stronger base but weaker nucleophile than cyanide ion. Signup and view all the answers

What is the effect of steric hindrance on nucleophilicity?

Steric hindrance decreases nucleophilicity. Signup and view all the answers

What are the four key factors that contribute to nucleophilicity?

Charge, electronegativity, solvent, and steric hindrance. Signup and view all the answers

What is the optimal temperature range for the reaction mixture to prevent spontaneous decomposition of the diazonium salt?

Below 5 ˚C Signup and view all the answers

What is the purpose of adding 10 drops of concentrated HCl to the aniline solution?

To lower the pH of the solution Signup and view all the answers

What is the role of 2-naphthol in the azo coupling reaction?

It undergoes nucleophilic attack by the diazonium ion Signup and view all the answers

Why is it important to add the NaNO2 solution slowly to the aniline solution?

To prevent the internal temperature from rising above 10 ˚C Signup and view all the answers

What is the purpose of stirring the mixture in the ice-water bath for 3-5 minutes?

To allow the Sudan I dye to form Signup and view all the answers

What is the purpose of vacuum filtering the precipitates?

To collect the Sudan I dye Signup and view all the answers

What is the role of β-naphthol in the synthesis of Sudan I?

It is the reactant that undergoes azo coupling Signup and view all the answers

Why is it necessary to chill the NaNO2 solution in the ice-water bath?

To maintain the temperature below 10 ˚C Signup and view all the answers

Study Notes

Bond Cleavage

Hemolytic cleavage (homolysis): a cleavage of a covalent bond in which the two electrons are divided equally between the products, resulting in electrically neutral fragments called free radicals.
- Example: Br-Br → 2Br·
Heterolytic cleavage (heterolysis): a cleavage of a covalent bond in which the shared pair of electrons remains with one of the fragments, resulting in ions.
- Example: R-CH2-X → R-CH2+ + X-

Bond Dissociation Energy

The amount of energy required to cleave a chemical bond.

Acid-Base Reactions

Bronsted-Lowry definition of acids and bases:
- Acids: species that donate a proton (H+)
- Bases: species that accept a proton
Example: HO- + H2O → H2O + HO-

Nucleophilicity

Factors that make a good nucleophile:
1. Charge: a nucleophile is more effective when it is electron-rich
2. Electronegativity: a nucleophile is more effective when it has a high electronegativity
3. Solvent: the solvent can affect the nucleophilicity of a species
4. Steric hindrance: the size and shape of the nucleophile can affect its ability to attack
Basicity is a subset of nucleophilicity: a nucleophile can donate a lone pair of electrons to a hydrogen atom (basicity) or to any other atom (nucleophilicity)

Pinacol Rearrangement

A method for converting a 1,2-diol to a carbonyl compound
Mechanism:
1. Protonation of the hydroxide ion
2. Formation of a carbocation
3. Rearrangement to form a new bond
4. Removal of a hydrogen ion to form the product
Procedure:
1. Mix pinacol hydrate with sulfuric acid
2. Distill the mixture until the upper layer of distillate ceases to increase in volume
3. Repeat the process several times to obtain the desired product

Synthesis of Sudan I

A two-step synthesis:
1. Activation of 2-naphthol under alkaline conditions to form 2-naphtholate
2. Azo coupling with the diazonium salt to form the Sudan I dye
Procedure:
1. Mix aniline with water and HCl
2. Chill the mixture in an ice-water bath
3. Add NaNO2 solution to the aniline mixture
4. Stir the mixture and transfer it to a beaker containing β-naphthol
5. Stir the mixture in the ice-water bath for 3-5 minutes
6. Vacuum filter the precipitates and wash with cold water

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Description

Learn about the two classifications of bond cleavage, Hemolytic cleavage, and its characteristics in a covalent bond. Understand the formation of free radicals and electronically symmetrical bond cleavage.