Molecular Structure of Diisopropyl Sulfide as Determined by Gas Electron Diffraction

Abstract

The molecular structure of diisopropyl sulfide has been investigated by gas-phase electron diffraction at 20°C. The most stable conformer has C₂ symmetry as shown in Fig.1 and Table 4. The important distances (r_g) and angles (∠_α) with the estimated limits of error are r(S-C) =1.830(3)A, r(C-C) =1.530(2)Å, ∠CSC = 103.5(12)°, ∠SCC₃ = 113.5 (4)°, ∠SCC₄=106.4(4)°, ∠CCC=111.3(8)°, and φ₁(CSCH) =57(8)°. Conformational analysis has been made on the basis of Models II and III (see Table 4). The relative abundance of the most stable conformer has been determined to be about 80±20% but no definite conclusion has been drawn on the concentrations of C_s and/or C₁ conformers.
The value of ∠SCC₃ is about 7° larger than that of ∠SCC₄. As found from Fig.1, this means that two isopropyl groups tilt away from each other as compared with the case of equal bond angles. The difference observed in the SCC angles of di-t-butyl sulfide is 10.5°, a value which is larger than the above difference in diisopropyl sulfide. The values of r_g(C-S) and
CSC in diisopropyl sulfide are about 0.02Å and 5° larger than those of dimethyl sulfide, respectively (see Table 6). The observed structures of the most stable conformers of diisopropyl ether, diisopropylamine and diisopropyl sulfide are compared with the results of molecular mechanics (MM 2) calculations in Table 7. The calculated values of ∠COC, ∠CNC and ∠CSC are about 3° smaller than the observed ones. The calculated dihedral angles are different from the observed ones by 3° to 13°.