Question

Which of the following correctly represents the +I effect of the substituents? (1) \(\mathrm{O}>\mathrm{COO}>\mathrm{CR}_{3}\) (2) \(\mathrm{COO}>\mathrm{O}>\mathrm{C} \mathrm{R}_{3}\) (3) \(\mathrm{O}<\mathrm{COO}<\mathrm{CR}_{3}\) (4) \(\mathrm{COO}<\mathrm{O}<\mathrm{CR}_{3}\)

Short answer

(3) \(\textbackslash O \textless \textbackslash COO \textless \textbackslash CR_{3}\).

Step-by-step solution

Understand the +I Effect

The +I effect (positive inductive effect) refers to the electron-releasing property of a substituent through a sigma bond. Substituents that donate electrons have a stronger +I effect.

Identify the Given Substituents' +I Effect

Evaluate the +I effect of the substituents based on their ability to release electrons. Generally, alkyl groups lead the +I effect.

Compare the Substituents’ +I Effect

Order the given substituents from highest to lowest based on the +I effect: 1. \(\textbackslash CR_3\)2. \(\textbackslash COO\)3. \(\textbackslash O\). This ordering is because \(\textbackslash CR_3\) has the strongest +I effect followed by \(\textbackslash COO\) and \(\textbackslash O\) having the weakest.

Compare with Options

Select the option that matches this order: (3) \(\textless O\)<\(\textless \ COO\)< \(\textless CR_3\).

Key concepts

Inductive Effect

The **inductive effect** is an electrical effect observed in organic chemistry. It refers to the transmission of charge through a chain of atoms in a molecule, due to the electronegativity differences between atoms. Imagine pulling a string; the force is felt along the string's length. This effect is similar but involves electrons.
The inductive effect can be positive (+I) or negative (-I). The positive inductive effect occurs when a substituent donates electrons through sigma bonds, increasing electron density on adjacent atoms. Substituents like alkyl groups (e.g., \(\textbackslash CR_3\)) exhibit a strong +I effect. These groups push electrons toward the carbon chain, stabilizing positive charges.
Conversely, the negative inductive effect (-I) happens when a substituent withdraws electrons, decreasing electron density. Typically, electronegative atoms or groups (like halogens or nitro groups) show a -I effect.

Substituents

Substituents are atoms or groups of atoms that replace a hydrogen atom in a hydrocarbon. They play a significant role in determining the chemical and physical properties of molecules.
When analyzing inductive effects, it’s essential to understand the substituent's nature. Here are a few common substituents and their effects:

• **Alkyl groups (\(\textbackslash CR_3\))**: These groups are electron-releasing. They have a strong +I effect due to their ability to donate electrons via sigma bonds.
• **Carboxyl group (\(\textbackslash COO\))**: This group exhibits a moderate +I effect. While it has oxygen atoms (which are electronegative), its overall nature makes it less electron-releasing than alkyl groups.
• **Hydroxyl group (\(\textbackslash O\))**: Oxygen, being highly electronegative, tends to withdraw electrons. Thus, it has a weaker +I effect compared to alkyl and carboxyl groups.

Knowing how different substituents affect electron distribution helps in predicting the stability and reactivity of molecules.

Electron-Releasing Property

The **electron-releasing property** of a substituent describes its ability to donate electrons through sigma bonds. This property is crucial in understanding the +I effect.
Substituents with a strong electron-releasing ability stabilize positive charges on the molecule, making certain chemical reactions more favorable. The order of electron-releasing strength typically follows this pattern:

• **Alkyl groups (\(\textbackslash CR_3\))**: These have the highest electron-releasing capability, leading to the strongest +I effect.
• **Carboxyl group (\(\textbackslash COO\))**: Moderate in terms of electron-releasing property, these groups are less potent than alkyl groups but still exhibit a noticeable +I effect.
• **Hydroxyl group (\(\textbackslash O\))**: Known for their electron-withdrawing nature, these groups have a weaker +I effect.

Understanding these properties helps in predicting how different substituents will influence the molecule's overall electron distribution.