Which of the statements (A‐D) given below are correct for B2H6 molecule: A. Addition of Et2O•BF3 to NaBH4 in a polyether solvent produces B2H6. B. It has D2d symmetry. C. Reaction of B2H6 with NMe3 gives Me3N•BH3. D. It is diamagnetic.
A, C and D
Understanding B2H6 (Diborane)
B2H6, commonly known as diborane, is a chemical compound containing boron and hydrogen. It is a dimer of BH3. Diborane is an important reagent in organic chemistry and is known for its unique structure involving 3-center-2-electron bonds.
Analyzing Statements about B2H6 Molecule
Let's evaluate each given statement regarding the B2H6 molecule to determine its correctness.
Statement A: B2H6 Synthesis
Statement A says that the addition of Et2O•BF3 to NaBH4 in a polyether solvent produces B2H6. This is a common laboratory method for the synthesis of diborane. Sodium borohydride (NaBH4) acts as a source of hydride ions, and boron trifluoride etherate (Et2O•BF3) provides the boron. The reaction proceeds as follows:
\(3\text{NaBH}_4 + 4\text{BF}_3 \xrightarrow{\text{Ether solvent}} 2\text{B}_2\text{H}_6 + 3\text{NaBF}_4\)
This statement is correct.
Statement B: B2H6 Symmetry
Statement B claims that B2H6 has D2d symmetry. The structure of diborane involves two bridging hydrogen atoms and four terminal hydrogen atoms. The two boron atoms and the four terminal hydrogen atoms lie in one plane, while the two bridging hydrogen atoms lie in a plane perpendicular to the first plane, symmetrically positioned above and below the B-B axis. This structure possesses a center of inversion. The correct point group symmetry for diborane (B2H6) is D2h, not D2d. The D2d point group lacks a center of inversion, which is present in B2H6.
This statement is incorrect.
Statement C: B2H6 Reaction with NMe3
Statement C states that the reaction of B2H6 with NMe3 gives Me3N•BH3. Trimethylamine (NMe3) is a strong Lewis base. Diborane reacts with Lewis bases, undergoing cleavage. Strong Lewis bases like NMe3 cause symmetric cleavage of the diborane dimer, forming adducts with the monomeric borane (BH3) unit.
\(\text{B}_2\text{H}_6 + 2\text{NMe}_3 \rightarrow 2\text{Me}_3\text{N} \cdot \text{BH}_3\)
This statement is correct.
Statement D: B2H6 Magnetic Property
Statement D claims that B2H6 is diamagnetic. A substance is diamagnetic if all its electrons are paired. Boron has 3 valence electrons, and hydrogen has 1. In B2H6, all 12 valence electrons (2×3 + 6×1) are involved in bonding, including the terminal B-H sigma bonds and the bridging 3-center-2-electron B-H-B bonds. All these electrons exist as pairs. Since there are no unpaired electrons in the B2H6 molecule, it is diamagnetic.
This statement is correct.
Conclusion on B2H6 Statements
Based on the analysis:
- Statement A is correct (Synthesis).
- Statement B is incorrect (Symmetry is D2h).
- Statement C is correct (Reaction with NMe3).
- Statement D is correct (Diamagnetic property).
Therefore, the correct statements for the B2H6 molecule are A, C, and D.
Important Questions from p - Block
Which of the following has the lowest boiling point?
Which of the following reaction(s) do(es) NOT occur
(i) [NPCl2]3 + 6 NaF \(\rm \xrightarrow[reflux]{MeCN}\) [NPF2]3 + 6 NaCl
(ii) n PCl5 + n NH4Cl \(\rm \xrightarrow[reflux]{C_6H_5Cl}\) [NPCl2]n + 4 n HCl [n = 3, 4, 5]
(iii) n PF 5 + n NH 4 F \(\rm \xrightarrow[reflux]{C_6H_5Cl}\) [NPF 2 ] n + 4 n HF [n = 3, 4, 5]
Choose the correct statement(s) from the following:
(i) The trend in Lewis acidity among silicon halides is SiI4 < SiBr4 < SiCl4 < SiF4.
(ii) Tin(II) chloride can act as a Lewis acid and not as a Lewis base.
(iii) Aluminosilicates can display Brønsted acidity.
Consider following statements
A. PbCl2 has low solubility in water.
B. Sulfides of As(III) and Sb(III) are soluble in ammonium sulfide.
C. SnS is soluble in yellow ammonium sulfide.
D. MnS is precipitated by passing H2S through acidic MnCl2.
Correct statements are
Among Si3N4, α-BN, AlN and (SN)x, the compound with the highest conductivity is
