Nucleophiles attack at that part of the substrate molecule which is electron deficient. The reaction in which a nucleophile replaces an already existing nucleophile in a molecule is called a nucleophilic substitution reaction. Haloalkanes are substrates in these reactions. In this type of reaction, a nucleophile reacts with a haloalkane (the substrate) having a partial positive charge on the carbon atom bonded to halogen. A substitution reaction takes place, and the halogen atom, called the leaving group, departs as a halide ion. Since the substitution reaction is initiated by a nucleophile, it is called a nucleophilic substitution reaction.
\(Nu^− +C-X →C-Nu+X^−\)
When sodium hydroxide (NaOH) reacts with a haloalkane (R-X), the predominant product is an alcohol. This process exemplifies a nucleophilic substitution reaction.
Nucleophiles, such as the hydroxide ion (\(\text{OH}^-\)) derived from NaOH, target electron-deficient molecular sites. In this reaction, the haloalkane (R-X) functions as the substrate, where 'R' denotes an alkyl group and 'X' represents a halogen. Due to the halogen's higher electronegativity compared to carbon, the carbon atom develops a partial positive charge, rendering it vulnerable to nucleophilic assault.
The \(\text{OH}^-\) ion displaces the halogen atom because of its nucleophilic character, yielding an alcohol (\(R-\text{OH}\)) and liberating a halide ion as a byproduct.
Nu^-+C-X→C-Nu+X^−
In this formulation:
This reaction mechanism dictates that the nucleophile (hydroxide ion) substitutes the leaving group (halogen), culminating in alcohol formation and establishing it as the primary reaction product.
A nucleophilic substitution occurs when KCN reacts with an alkyl halide (R-X). The cyanide ion (CN−), acting as a nucleophile from KCN, targets the electron-deficient carbon atom in R-X. This carbon atom is bonded to a halogen (X), which is electron-withdrawing. The halogen is then substituted by the nucleophile, generating the target compound.
\(R-X+KCN→R-CN+KX\)
Key components of this reaction include:
Consequently, the primary product synthesized is a nitrile (R-CN).
Here's why:
This nucleophilic substitution reaction yields an isonitrile, where R is bonded to the isocyanide (CN) group.
The major product of the reaction between AgCN and R-X is isonitrile.
Nucleophilic substitution occurs when a nucleophile attacks a partially positively charged carbon atom:
\(R-X + AgCN → R-NC + AgX\)
R-NC represents an isonitrile. Therefore, the correct answer is isonitrile.
In this reaction, potassium nitrite (KNO2) provides the nucleophile, the nitrite ion (NO2-). R-X represents a haloalkane, where R is an alkyl group and X is a halogen. The carbon atom bonded to the halogen in a haloalkane carries a partial positive charge, making it susceptible to nucleophilic attack. The reaction proceeds via a nucleophilic substitution mechanism, where one nucleophile replaces another.
Nucleophilic substitution reactions generally follow the pattern:
\(Nu^− +C-X →C-Nu+X^−\)
In this specific reaction:
The NO2- ion, acting as the nucleophile, attacks the carbon atom bonded to the halogen (X). This results in the displacement of the halide ion and the formation of an alkyl nitrite as the primary product.
| Reactants | Product |
|---|---|
| R-X + KNO2 | R-O-N=O |
Therefore, the reaction of KNO2 with R-X predominantly yields alkyl nitrite, R-O-N=O. This synthesis exemplifies a standard nucleophilic substitution mechanism, with the nitrite ion functioning as the nucleophile to produce an alkyl nitrite.
Nucleophilic substitution reactions are fundamental in organic chemistry. In these reactions, an electron-rich nucleophile attacks an electron-deficient carbon atom, typically in haloalkanes (R-X). The halogen (X) functions as the leaving group, being displaced by the nucleophile.
An illustration of this is the reaction between ammonia (NH3) and a haloalkane (R-X). Ammonia, acting as the nucleophile, attacks the carbon atom. The process involves the nucleophile (NH3) substituting the leaving group (X) on the substrate (R-X).
The general reaction mechanism is:
\(NH_3 + R-X \rightarrow R-NH_3^+ + X^-\)
The initial product formed is an alkylammonium ion (R-NH3+). Subsequent deprotonation of this ion yields a primary amine (R-NH2).
\(R-NH_3^+ + OH^- \rightarrow R-NH_2 + H_2O\)
Consequently, the primary product of the reaction between NH3 and R-X is a primary amine. This outcome is due to the efficiency of the nucleophilic substitution in replacing the halide ion with the amine group.
| Reactant | Major Product |
|---|---|
| NH3 + R-X | Primary Amine (R-NH2) |
Given below are two statements:
Statement (I): Alcohols are formed when alkyl chlorides are treated with aqueous potassium hydroxide by elimination reaction.
Statement (II): In alcoholic potassium hydroxide, alkyl chlorides form alkenes by abstracting the hydrogen from the $ \beta $-carbon.
In the light of the above statements, choose the most appropriate answer from the options given below: