Isomeric Compounds of OMCTS, DFT Calculations

We have carried out DFT (B3LYP/6-31G(d)) calculations (the basis set comprises 312 cGTOs) in order to establish the energetic order of the different possible isomers of (Me2Si-NH)4, OMCTS (Fig. 15). At the local minima on the potential energy surfaces, the Hessian matrices were computed. Harmonic vibrational frequencies were used to calculate the zero-point vibration-corrected energetics. (Results are collected in Table I and Fig. 16.) 

Relative Energies of the Different Isomers and Conformers of OMCTS (B3LYP/6-31G(d) 

Note E denotes the electronic energy while E0 includes zero-point vibrational effects. 

05 pm and the torsional angles differ strongly. With only one two-fold symmetry axis and two symmetry planes, isomer A2 exhibits C2V symmetry. 

In single crystals of OMCTS,53 two conformers - the chair-(Al) and the boat-form (A2) - are found (see Fig. 15). The calculated most stable twist conformation A appears only in the unsymmetrical [(Me3C)2Si-NH-SiMe2NH]2. 

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