Question

The number of nucleophiles in the following list is: \[ CH_3NH_2, \quad CH_3CHO, \quad C_2H_4, \quad CH_3SH \]

• A. \( 1 \)
• B. \( 2 \)
• C. \( 4 \)
• D. \( 3 \)

Hint:

To identify nucleophiles, look for species with lone pairs (e.g., amines, thiols) or negative charges. Aldehydes and alkenes generally act as electrophiles, not nucleophiles.

Answer 1

The Correct Option is B

Nucleophiles are species that have a pair of electrons to donate and typically carry a negative charge, or are neutral molecules with lone pairs or π-bonds that can form new bonds with electrophiles.

Let's examine each compound:

1. CH₃NH₂ (methylamine): 
   This molecule has a lone pair of electrons on the nitrogen atom, making it a nucleophile.
2. CH₃CHO (acetaldehyde):
   Although it contains a polar C=O bond, it acts as an electrophile because the carbon is electron-deficient.
3. C₂H₄ (ethylene):
   This is a neutral molecule with π-bonds, which can act as a weak nucleophile.
4. CH₃SH (methanethiol):
   The sulfur atom has a lone pair, making this compound a good nucleophile.

From the list, CH₃NH₂ and CH₃SH are nucleophiles because they have atoms with lone pairs of electrons available for donation.

Therefore, the number of nucleophiles is: 2.

Answer 2

Nucleophiles are species that donate an electron pair to an electrophile to form a chemical bond. They are often negatively charged or have a lone pair of electrons. Let's examine each molecule:

• \(CH_3NH_2\) (Methylamine): The nitrogen atom has a lone pair of electrons, making it a nucleophile.
• \(CH_3CHO\) (Acetaldehyde): The oxygen atom has two lone pairs, and while the carbonyl carbon is electrophilic, the molecule itself can act as a nucleophile through the oxygen's lone pairs.
• \(C_2H_4\) (Ethene): This molecule has a double bond but no lone pairs. It acts as an electrophile, not a nucleophile.
• \(CH_3SH\) (Methanethiol): The sulfur atom has two lone pairs of electrons, making it a nucleophile. Sulfur is larger and more polarizable than oxygen, so thiols are generally better nucleophiles than alcohols.

Therefore, there are two nucleophiles in the list: \(CH_3NH_2\) and \(CH_3SH\).