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Question #44150

Difficulty: 8/10 | 🟢 Free

The Question

Consider the molecules trimethylamine, $\ce{N(CH3)3}$ (Compound X), and trisilylamine, $\ce{N(SiH3)3}$ (Compound Y). Evaluate the following statements regarding their structural and chemical properties at $298\text{ K}$ :

I. Compound X is more basic than Compound Y in the gas phase, but Compound Y becomes more basic in aqueous solution due to superior hydrogen bonding and solvation of the $\ce{[HN(SiH3)3]+}$ cation. II. The geometry around the central nitrogen atom is trigonal pyramidal in Compound X and trigonal planar in Compound Y. III. Compound X readily forms a stable Lewis acid-base adduct with $\ce{BF3}$ , whereas Compound Y does not react with $\ce{BF3}$ . IV. The $\ce{N-Si}$ bond length in Compound Y is significantly shorter than the sum of their single-bond covalent radii.

Which of the following combinations of statements is correct?

Options

A.
II, III, and IV only
B.
I, II, and IV only
C.
II and IV only
D.
I, II, III, and IV

Check Your Answer

Correct Answer

Step-by-Step Solution

Explanation

How the Examiner Thinks

Exception_Exposure

Learn to identify edge cases and boundary exceptions that JEE examiners hide in math problems.

Concepts Behind This Question

Back Bonding Strength|Basicity-Solvation Competition|Amines - Class 12

Why This Question Is Tricky

Common Mistakes

The question tests the student's ability to prioritize fundamental electronic effects ( $p\pi-d\pi$ back-bonding) over thermodynamic phase effects (solvation).

A common trap in amine basicity is the 'solvation competition' seen in methylamines in water, where solvation of the conjugate acid alters the basicity order.

Students falling for this trap might assume that aqueous solvation could make protonated trisilylamine stable in water.

However, the 'Hidden Variable' is that back-bonding completely delocalizes the lone pair, making the initial protonation electronically unfeasible, thus rendering any subsequent solvation stabilization moot.

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	Chemical Bonding and Molecular Structure - Class 11 Part 1
Concept	Back Bonding Strength
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free