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Which is/are the correct statement/s about structure of methyl isothiocyanate (H3CNCS) and Silyl isothiocyanate(SiH3NCO)?

(A) CNC bond angle in H3CNCS is >120 and hybridization is closed to sp2 

(B) Si-N-C bond angle is 180 in H3CNCS
(C) Both have Back Bonding 
(D) Skeleton Si-N-C-S is linear but molecule are non planer.

SOLUTION:  

The hybridization of Nitrogen in Methyl isothiocyanate (H3CNCS) is Sp2. Thus bond angle (< C-N-C) is expected to be 120°. But it is slightly greater than 120° due to resonating structure. The resonating structure has N as sp hybridized. Hence bond angle of the overall structure is found to be about 142°


But in case Silyl isothiocyanate (SiH3NCO), the structure is found to be (sp hybridized) and planar  due to back bond between Si-N. In which the lone pair of electrons on N are donated to the vacant 3d orbitals of Si through back bonding (2pπ-3dπ back bond).



Hence Options (A, B, D) are correct.

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