Relative energies, stereoelectronic interactions and conformational interconversions in silathiacyclohexanes

Abstract Stereoelectronic hyperconjugative interactions and the relative energies of conformers and transition states of 2‐, 3‐, and 4‐silathiacyclohexane were calculated at the B3LYP/6–311+G(d,p) level of theory. The chair conformer of 2‐silathiacyclohexane is 15.4 and 15.9 kcal mol−1 (1 kcal = 4.184 kJ), respectively, lower in energy than the chair conformers of 3‐ and 4‐silathiacyclohexane. Intrinsic reaction path calculations were used to connect the transition states between the respective chair and twist conformers and different chair–chair conformational interconversion paths were located for 3‐ and 4‐silathiacyclohexane. The energy of the transition state that connects the chair and 2,5‐twist conformers of 3‐silathiacyclohexane is 5.58 kcal mol−1 higher in energy than the chair. The transition state that connects the chair and 2,5‐twist conformers of 4‐silathiacyclohexane is 4.82 kcal mol−1 higher in energy than the chair. The energy differences (ΔE, kcal mol−1) between the chair conformer of 2‐silathiacyclohexane and the respective 1,4‐twist (ΔE = 4.16), 2,5‐twist (ΔE = 3.20) and 3,6‐twist (ΔE = 3.87) conformers were calculated. Small relative energy differences were calculated between the chair conformer and the respective 1,4‐twist (ΔE = 3.95), 2,5‐twist (ΔE = 4.07) and 3,6‐twist (ΔE = 3.46) conformers of 3‐silathiacyclohexane. The calculated energy differences (ΔE) between the chair conformer and the 1,4‐twist and 2,5‐twist conformers of 4‐silathiacyclohexane were 3.50 and 4.04 kcal mol−1, respectively. The geometric parameters and stereoelectronic hyperconjugative interactions in the silathiacyclohexanes are compared and discussed. Copyright © 2004 John Wiley & Sons, Ltd.