What is a nucleophilic addition reaction?
A nucleophilic addition reaction is to be defined as a chemical addition reaction in which the nucleophile forms a sigma bond with an electron deficient species. These types of reactions are considered very important in the field of organicchemistry. These reactions enable the conversion of carbonyl groups into a variety of functional groups. There are three basic steps that are followed:
- The electrophilic carbonyl carbon will lead to formation of a sigma bond with the nucleophile.
- The carbon-oxygen pi bond is broken, that lead to the forming alakesideintermediate.
- The subsequent protonation of the lakeside yields the alcohol derivative.
The carbon-oxygen double bond will be directly attacked by strong nucleophiles thatwill give rise to the lakeside. In this case the weak nucleophiles are used; the carbonyl group will be activated with the help of an acid catalyst for the nucleophilic addition reaction to proceed.
In the reaction above, the coplanar structure of the compound and the carbon atom in in Sp2 hybridized state. In the reaction, we will see that the nucleophile will attach on the C=O group. This will result in the breakage of the pi bond. The carbonyl carbon will undergo the hybridization and formation of sigma bond with the nucleophile.
CARBONNLY COMPOUNDS AND NEUCLEOPHILE ADDITION REACTION?
In all type of carbonyl compound, the bond between carbon and oxygen is polar. It is being noticed that the electron density is higher when it is near the oxygen atom. This reaction will lead to the generation of a partial negative charge on to the oxygen atom. This reaction will also create a partial positive charge on the carbon atom.
In this case, we can see that the carbonyl carbon holds a partial positive charge, soit behaves as an electrophile. This partial negative charge on the oxygen atom can be stabilized with the introduction of an acidic group. In the reaction process, the proton donated by the acid bonds with the carbonyl oxygen atom and that will neutralizes the negative charge.
Aldehydes are relatively more reactive tin case of nucleophilic addition reactions as compared to ketones. This isalso because the secondary carbocation’s that are formed by ketones are stabilized by the adjacent R groups. The primary carbocation’s formed by aldehydes are less stable as compared to the secondarycarbonations that is formed by ketones and so they are susceptible to nucleophilic attacks.
Reactions with Hydrogen Cyanide
The nucleophilic addition reactionthat takes place between the hydrogen cyanide (HCN) and carbonyl compounds will form cyanohydrins .In this case the base catalysts are often used to increase the rate of the reaction. The reaction process is better explained below:
The polar nature of the C=O bond will make the carbonyl carbon electrophilic in nature. Subsequently the cyanide anion executes a nucleophilic attack on the carbonyl carbon that results in the formation of an intermediate.
Nucleophilic Additions with Monohydric Alcohols
Aldehydes and ketones willundergo nucleophilic addition reactions with monohydric alcohols to form hemiacetals in the next process where they react with another molecule of alcohol, an acetal is obtained there will always a need to catalyst so that the reaction can be carried out in a proper manner.
The hemiacetals can undergo hydrolysis to form the reactants. In this reaction, the carbonyl oxygen is protonated justbefore the nucleophilic attack is carried out by the alcohol. The nucleophilic alcohol will be deprotonated to form the hemiacetals. The reactionis to be repeated to obtain the acetal.
Nucleophilic Addition with Grignard Reagents
The polar nature of Grignard reagents will attribute to a partial negative charge to the carbon atom. The reaction will lead to the formation of the following alcohols from nucleophilic addition reactions with Grignard reagents.
- Primary alcohols will be formed when formaldehyde is used.
- The reaction between the aldehydes and the Grignard reagents will give us secondary alcohols.
- Reaction between ketones and the Grignard reagents will give us tertiary alcohols
In the general form the reactionsinvolves the attack of the nucleophilic carbon that R-Mg-Xon the carbonyl carbon.
Reaction with Primary Amines
This reaction between the primary amines and ketones will form amine derivate along with water. The reaction is explained below:
At the initial stage, the nucleophilic nitrogen belonging to the amine attacks the carbonyl carbon. The double bond is broken and a new carbon-nitrogen sigma bond will be formed. In the second step a proton is transferred from the amine to the oxygen atom. The nucleophilic addition reaction takes place where the OH group is further protonated and water gets removed. The carbon atom will form a double bond with the nitrogen belonging to the amine
Interesting and helpful resource: aldehydes,ketones and carboxylic acids from class 12 chemistry – find all the questions & answers
