Question

Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R Assertion A: Carbenes are highly reactive neutral species containing a divalent carbon atom with six valence electrons. Reason R: Carbenes are electron deficient species because the carbon atom does not complete its octet, making them unstable and highly reactive. In the light of the above statements, choose the most appropriate answer from the options given below
• Both A and R are correct and R is the correct explanation of A
• Both A and R are correct but R is NOT the correct explanation of A
• A is correct but R is not correct
• A is not correct but R is correct

• A. 1
• B. 2
• C. 3
• D. 4

Hint:

Carbenes are:
• Neutral reactive intermediates
• Divalent carbon species
• Electron deficient with only six valence electrons Incomplete octet makes them highly reactive.

Answer 1

The Correct Option is A

Concept: Carbenes are very important reactive intermediates in organic chemistry. A carbene is a neutral species containing: \[ \boxed{\text{A divalent carbon atom}} \] A general representation is: \[ \mathrm{:CR_2} \] where carbon forms two covalent bonds and possesses only six electrons in its valence shell. Because the octet of carbon remains incomplete, carbenes are highly unstable and therefore highly reactive. Carbenes can exist in:
• Singlet state
• Triplet state But in both cases, the carbon atom remains electron deficient.

Step 1: Examine Assertion A carefully. Assertion A states: “Carbenes are highly reactive neutral species containing a divalent carbon atom with six valence electrons.” This statement is correct. Let us understand why. A carbene carbon:
• Forms two covalent bonds.
• Possesses only six electrons around carbon. For example, methylene carbene: \[ \mathrm{:CH_2} \] Here carbon is attached to:
• Two hydrogen atoms
• One lone pair or unpaired electrons depending on state Total electrons around carbon become: \[ 6 \] instead of the stable octet value: \[ 8 \] Thus, carbene carbon is divalent and electron deficient. Therefore, Assertion A is correct.

Step 2: Examine Reason R carefully. Reason R states: “Carbenes are electron deficient species because the carbon atom does not complete its octet, making them unstable and highly reactive.” This statement is also correct. In stable organic compounds, carbon generally obeys the octet rule. But in carbenes:
• Carbon has only six electrons.
• Octet remains incomplete.
• Electron deficiency creates instability. Because unstable species try to attain stability rapidly, carbenes react very quickly. Thus: \[ \boxed{ \text{Electron deficiency } \Rightarrow \text{ High Reactivity} } \] Hence, Reason R is correct.

Step 3: Determine whether R explains A correctly. Assertion says:
• Carbenes are highly reactive.
• They contain six valence electrons. Reason explains:
• Carbon does not complete octet.
• Therefore carbenes become unstable and reactive. Thus, the reason directly explains why carbenes are highly reactive. Hence:
• Assertion A is correct.
• Reason R is correct.
• Reason R correctly explains Assertion A. Additional Understanding: Carbenes participate in many important reactions such as:
• Cyclopropanation reactions
• Insertion reactions
• Addition to double bonds Their high reactivity arises mainly due to incomplete octet configuration. Final Conclusion: Both Assertion A and Reason R are correct, and Reason R correctly explains Assertion A. Hence, the correct answer is: \[ \boxed{(1)} \]