Question

Which statement is correct for the following structures 1 and 2?
Statement (I): Black gram as a cover crop to reduce surface runoff and soil loss during rainy seasons.
Statement (II): Black gram as a live mulch crop to reduce surface runoff and soil loss during rainy seasons.
In light of the above statements, choose the most appropriate answer from the options given below.

• A. Both 1 and 2 are synthetic pesticides and are environmental friendly
• B. Compound 1 is plant originated while compound 2 is synthetic and persists for a long time in the environment
• C. Compound 1 is derived from the carbamate group while compound 2 is organochlorine
• D. Due to puckered structure compound 2 is degraded fast while compound 1 in active

Hint:

Steric strain and puckered conformations in pesticide molecules increase their free energy, making them highly vulnerable to microbial degradation compared to highly stable, symmetric conformations.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
The persistence and degradation rate of organic pesticides in the soil environment are heavily governed by their molecular geometry and spatial conformation.
Even when two compounds have identical chemical formulas, subtle differences in their stereochemical structure can create massive differences in their physical stability, metabolic pathways, and biological activity.
This question contains a typographical error in the print where agricultural agronomy text (regarding black gram as a cover crop/live mulch) was mistakenly pasted into the question body of a chemical structures question.
However, the options provided clearly reference the organic pesticide chemistry of two specific compounds (structures 1 and 2).

Step 2: Detailed Explanation:
Let us analyze the chemical principles behind the correct option:
In organic chemistry, saturated six-membered rings (such as cyclohexane derivatives, found in many organochlorine insecticides like hexachlorocyclohexane/HCH isomers) do not exist as flat, planar molecules due to ring strain.
Instead, they assume non-planar, puckered conformations—primarily the highly stable “chair” conformation and the less stable “boat” or “puckered” conformations.
In these conformations, substituents can occupy either equatorial positions (pointing outward along the perimeter) or axial positions (pointing vertically up or down).
Isomers that adopt a highly symmetric, stable chair conformation with all chlorine substituents in equatorial positions (such as \(\beta\)-HCH) are exceptionally resistant to chemical, biological, and enzymatic degradation.
Consequently, these isomers persist in the soil and environment for extremely long periods.
Conversely, isomers or related compounds that are forced into highly strained, unsymmetrical, or puckered conformations (structure 2) have much higher free energy.
This steric strain makes their chemical bonds more vulnerable to nucleophilic attack, enzymatic hydrolysis, and microbial degradation.
Therefore, the puckered structure of compound 2 allows it to be degraded rapidly in the environment, whereas the structurally stable and planar-active conformation of compound 1 remains highly persistent and active.
This matches option (D).

Step 3: Final Answer:
Consequently, the correct statement is represented by option (D).