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InterviewSolution
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The bond angle between two hybrid orgials is ` 105^(@)` . Calculate the percentege of s-character of the hybrid orbital .Given that cos ` 75^(@) = 0 .2588`. |
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Answer» ` cos alpha = - (1)/(m) ` where m = hybridisation index ` therefore - (1)/(m) cos 105^(@) = cos (180 - 75 ) = - cos ^(@) = - 0.2588 or m = (1)/(0.2588) = 3.86` % s-character ` = (1)/(1+m) xx10- = (1)/(1+3.86) xx100 = 20.58%` Alternatively , s-character decreases as the bond angle decreases. For example , `{:(" Hybrid orbital" " "sp^(3) " " sp^(2) " "sp),("s-character " " "25% " "33.3% " "50%),(" Bond angle "" " 109.5^(@) " " 120^(@) " "180^(@)):}` Thus, when bond angle decreases below ` 109.5^(2)`, the s-character will dcrease accordingly. Although the decrease is not linear , even then approsimate value can be calculated as follows : Decrease in angle = `120 - 109.5^(@) = 10.5^(@)` Decrease in s-character =` 33.3 - 25 = 83 ` Actual decrease in bond angle =` 109.5^(@) - 105^(@) = 4.5^(@)` ` therefore ` Expected decrease in s-character `= (8.3)/(10.5) xx4.5 = 3.56%` Thus, s-character should decrease by about 3.56% Hence, s-character = ` 25 - 3.56 = 21 .44%` |
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