| Popis: |
Isolated SiH stretching frequencies v is (SiH) are reported for the species SiHDX 2 (X = F or Cl), SiHD 2 NMe 2 , SiHD 2 OMe, (SiHD 2 NMe and (SiHD 2 ) 2 S. IR spectra in the gas and solid phases are also shown for CHD 2 OSiH 3 . Splittings of v as (CH 3 ) in (CH 3 ) 2 )SiH 2 and (CH 3 ) 3 SiH are reported, from which v is (CH) values are deduced. Evidence for the structures of these molecules is discussed. Ab initio structures have been determined using a 4–21G/3-3-21G basis set for the above molecules, and for SiH 4 , SiH 3 F, SiHF 3 , SiH 3 Cl, SiHCl 3 , SiH 3 Me, SiH 2 Me 2 , SiHMe 3 , SiH 3 CN, SiH 3 CCH, SiH 3 SiH 3 , SiH 3 CH 2 CH 3 , SiH 3 CH 3 Cl, SiH 3 CHCH 2 and CH 3 CH 2 CH 3 . The r e (SiH) and r e (CH) values are tabulated. A good correlation is found between v is (SiH) and r e (SiH) r e (SiH)(A) = 1.9089 − 1.998 × 10 −4 v is (SiH) (cm −1 ) Plots for SiH 2 Cl 2 , and SiHCl 3 reveal large anomalies, but SiH 3 CN and SiH 3 CCH behave normally. Results are compared with similar ones for CH bonds. The CH bond length asymmetry in Me 2 SiH 2 and Me 3 SiH revealed by the v as (CH 3 ) splittings is confirmed by the ab initio calculations. The effect of conformation on the β effect of methyl on SiH and CH bonds is explored. |
