A step by step mechanism for both the transformation of Robinson annulation sequence is to be provided, and the acidity of 2 − methylcyclohexane − 1 , 3 − dione with cyclohexanone is to be compared and explained. Concept introduction: Electrophiles are electron deficient species that have positive or partially positive charge. Lewis acids are electrophiles that accept electron pair. Nucleophiles are electron rich species that have negative or partially negative charge. Lewis bases are nucleophiles that donate electron pair. Free radical is an atom, molecule, or ion that has an unpaired electron that makes it highly chemically reactive. Substitution reaction: A reaction in which one of the hydrogen atoms of a hydrocarbon or a functional group is substituted by any other functional group is called substitution reaction. Elimination reaction: A reaction in which two substituent groups are detached and a double bond is formed is called elimination reaction. Addition reaction: It is the reaction in which unsaturated bonds are converted to saturated molecules by the addition of molecules. A base removes acidic hydrogen and forms an enolate. The enolate adds to the β − carbon of α , β − unsaturated carbonyl compound and forms a new carbon–carbon bond and a new enolate that undergoes protonation and forms the Michael addition product A carbon–carbon bond formation occurs by aldol addition and aldol condensation reaction. An aldol reaction takes place in a protic solvent with a base. An aldol reaction takes place by acid catalysis, and direct dehydration of β − hydroxy aldol intermediate forms α , β − unsaturated product. A chemical reaction that is catalyzed by an acid is called acid catalyzed reaction. A chemical reaction that is catalyzed by a base is called base catalyzed reaction. Aldol reaction is preferred in basic condition over acidic condition, as after the aldol condensation, acid catalysis promotes the reaction further. In Robinson annulation reaction, Michael addition, followed by simple aldol condensation, takes place. The Robinson annulation reaction is used to form one ring on to another. A resonance structure which stabilize the conjugate base also increases the acidity. The rules for drawing resonance structures are as: Only nonbonding electron pairs and pi electrons can participate in conjugation in the formation of various resonating structures. The single bonds present in the molecule do not break or form in the resonance structures. The placement of atoms present in the molecule remains fixed. The octet of all atoms is completely filled. More the number of resonance structures indicate higher stability of a compound.

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Chapter 19, Problem 21PP

Interpretation Introduction

Interpretation:

A step by step mechanism for both the transformation of Robinson annulation sequence is to be provided, and the acidity of 2−methylcyclohexane−1,3−dione with cyclohexanone is to be compared and explained.

Concept introduction:

Electrophiles are electron deficient species that have positive or partially positive charge. Lewis acids are electrophiles that accept electron pair.

Nucleophiles are electron rich species that have negative or partially negative charge. Lewis bases are nucleophiles that donate electron pair.

Free radical is an atom, molecule, or ion that has an unpaired electron that makes it highly chemically reactive.

Substitution reaction: A reaction in which one of the hydrogen atoms of a hydrocarbon or a functional group is substituted by any other functional group is called substitution reaction.

Elimination reaction: A reaction in which two substituent groups are detached and a double bond is formed is called elimination reaction.

Addition reaction: It is the reaction in which unsaturated bonds are converted to saturated molecules by the addition of molecules.

A base removes acidic hydrogen and forms an enolate.

The enolate adds to the β− carbon of α,β− unsaturated carbonyl compound and forms a new carbon–carbon bond and a new enolate that undergoes protonation and forms the Michael addition product

A carbon–carbon bond formation occurs by aldol addition and aldol condensation reaction.

An aldol reaction takes place in a protic solvent with a base.

An aldol reaction takes place by acid catalysis, and direct dehydration of β− hydroxy aldol intermediate forms α,β− unsaturated product.

A chemical reaction that is catalyzed by an acid is called acid catalyzed reaction.

A chemical reaction that is catalyzed by a base is called base catalyzed reaction.

Aldol reaction is preferred in basic condition over acidic condition, as after the aldol condensation, acid catalysis promotes the reaction further.

In Robinson annulation reaction, Michael addition, followed by simple aldol condensation, takes place.

The Robinson annulation reaction is used to form one ring on to another.

A resonance structure which stabilize the conjugate base also increases the acidity.

The rules for drawing resonance structures are as:

Only nonbonding electron pairs and pi electrons can participate in conjugation in the formation of various resonating structures.

The single bonds present in the molecule do not break or form in the resonance structures.

The placement of atoms present in the molecule remains fixed.

The octet of all atoms is completely filled.

More the number of resonance structures indicate higher stability of a compound.

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