Question

From 20 mg of partially methylated disilane,Si₂H_6-x(CH₃)_x,27.8cm³of hydrogen are evolved during alkaline hydrolysis at 294 K and 97400 Pa. 

(a) Why the Si-Si bond of the disilane reacts during hydrolysis? 

(b) Why the Si-H bonds of the disilane react during hydrolysis? 

(c) Calculate the degree of substitution x of the methylated disilane. 

(d) Write the complete reaction equation for the hydrolysis. 

(e) How many isomers can form the calculated compound? 

Give the structural formula for each isomer. 

Answer 1

(a) The Si-Si bond is coordination unsaturated and thus, has a tendency to react with nucleophilic reagents with the bond breakage. 

(b) Similar to all compounds with negatively polarised hydrogen, this bond also reacts with protons from water with formation of elemental hydrogen. 

(c) (CH₃)_xSi₂H_6-x

Molecular mass: 2Si  2 × 28.086 

(6-x) H  (6-x) × 1.008 

x CH₃ x  × 15.035 

 56.172 + 1.008 (6 – x) + 15.035 x = 62.22 + 14.027 x

Hence, the degree of substitution = 2 

Hence (for a symmetrical isomer):