Geminal²J(²⁹Si‐O‐²⁹Si) couplings in oligosiloxanes and their relation to direct¹J(²⁹Si‐¹³C) couplings

Abstract

Absolute values of (79) geminal (2)J((29) Si-O-(29)Si) couplings were measured in an extensive series of (55) unstrained siloxanes dissolved in chloroform-d. Signs of (2)J((29)Si-O-(29)Si) in some (9) silicon hydrides were determined relative to (1)J((29)Si-(1)H) which are known to be negative. It is supposed that positive sign of the (2)J((29)Si-O-(29)Si) coupling found in all studied hydrides is common to all siloxanes. Theoretical calculations for simple model compounds failed to reproduce this sign and so their predictions of bond length and angle dependences cannot be taken as reliable. Useful empirical correlations were found between the (2)J((29)Si-O-(29)Si) couplings on one side and the total number m of oxygen atoms bonded to the silicon atoms, sum of (29)Si chemical shifts or product of (1)J((29)Si-(13)C) couplings on the other side. The significance of these correlations is briefly discussed.

Siloxane‐Bond Formation Promoted by Lewis Acids: A Nonhydrolytic Sol–Gel Process and the Piers–Rubinsztajn Reaction

“…[15] Scheme 7. [72] This research will surely be useful in the analysis of siloxane compounds that have more complex structures and could not be analyzed to date. [24,68] through siloxane bonding.…”

Spectra edited by relative signs of homonuclear couplings of low abundance nuclei

“…The M( 13 C)‐M( 13 C) is doubly symmetrically 13 C (99 atom%) labeled 13 CH 3 (CH 3 ) 2 Si‐O‐Si(CH 3 ) 2 13 CH 3 sample. Preparation of these compounds was described elsewhere …”

“…The only exception is R = H, where for the molecular fragment 1 H‐ 29 Si‐O‐ 29 Si, the couplings are 1 J (Si,H) ~ 200 Hz and 3 J (Si‐O‐Si‐H) ~ 1 Hz. All this appears to be the key reason why signs of 2 J (Si‐O‐Si) couplings in siloxanes were published only very recently, the sign detection being partly because of the E.COSY‐type experiment on fragments with direct Si‐H bond and partly by the method published in this article.…”

“…linear systems) are briefly presented here on sample 3 . The results confirm that all 2 J (Si‐O‐Si) in siloxanes have positive values irrespective of the siloxane structure.…”

Synthesis of a polyethylene glycolylated polysiloxane system through a two‐step procedure and its compatibility

“…It could be seen that the Si peaks from Si(CH 3 ) 3 Si NMR spectra of dPDMSPEG and P(Si-g-dPDMSPEGA), as shown in Figure 2(c). 39,40 It is suggested that the expected product was synthesized and no unreacted Si H or generated Si OH. The peak at 6.8 ppm (peak a) was assigned to the terminals silicone of each repeating units.…”