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I protected a phenol with the TIPSCl/triethylamine procedure. The product was isolated by column (hexanes/EtOAc) and shows an extra singlet at 1.05 ppm in $\ce{CDCl3}$, integrating to ~10 H. Whatever this is I cannot find in under UV or various TLC stains ($\ce{KMnO4}$, vanilin, PMA). The integration of the peak goes smaller after one more column. Any suggestions? Thanks!

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  • $\begingroup$ Is there a corresponding bonus peak in the 13C? $\endgroup$ – orthocresol May 30 at 20:36
  • $\begingroup$ Found two extra peaks in the aliphatic region, 18.1, 17.8, 14.6, 14.2,12.4. I know two of these are the isopropyl and a CH3 from an ethyl, did not assign them though. $\endgroup$ – Wah May 30 at 20:41
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I believe some of your triisopropylsilyl chloride may be hydrolyzed triisopropylsilylol, $\ce{((CH3)2CH)3SiOH}$. That may gives you $\delta$ 1.04 and 12.4 (for $\ce{C}$ attached to $\ce{Si}$) in $\mathrm{^1H}$- and $\mathrm{^{13}C}$-NMR spectra, respectively. Compare the spectral values in Ref.1 and 2 (see below; corresponding $\ce{^{13}C}$ values are in red):

Spectral Data

References:

  1. A. Goti, M. Cacciarini, F. Cardona, A. Brandi, “A convenient access to (3S)-3-(triisopropylsilyl)oxy-1-pyrroline N-oxide, a useful intermediate for polyfunctionalized enantiopure indolizidine and pyrrolizidine synthesis,” Tetrahedron Letters 1999, 40(14), 2853–2856 (https://doi.org/10.1016/S0040-4039(99)00310-X).
  2. R. F. Cunico, L. Bedell, “The triisopropylsilyl group as a hydroxyl-protecting function,” J. Org. Chem. 1980, 45(23), 4797–4798 (https://doi.org/10.1021/jo01311a058).
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  • $\begingroup$ This is what I'd originally thought (usually stuff like R3SiOH or R3SiOSiR3 are byproducts from silyl protection). What stopped me from putting it forward was the multiplicity, as the big peak for TIPS should be a doublet. $\endgroup$ – orthocresol May 31 at 0:10
  • $\begingroup$ yes the singlet is what confuses me -- it looks like some other silylanes, maybe my TIPSCl have some TMS or TBDMS with it? $\endgroup$ – Wah May 31 at 0:21
  • $\begingroup$ Take an NMR of TIPSCl. $\endgroup$ – user55119 May 31 at 1:06
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    $\begingroup$ I appreciate your effort, and I'm not saying you're wrong, rather I don't know. I've never worked with TIPS groups, only TBS. Since I cannot judge whether the answer is correct or not, I refrain from voting. $\endgroup$ – orthocresol May 31 at 23:15
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    $\begingroup$ FWIW, for TIPSOH, Chem. Lett. 2014, 43 (4), 429–431 says δH 1.07 (m, 21 H) and δC 17.7, 12.3. Most other references e.g. Angew. Chem. Int. Ed. 2011, 50 (33), 7533–7536 give similar values, but somewhat intriguingly, Chem. Commun. 2016, 52 (70), 10625–10628 reports δH 1.43 (s, 21 H) and δC 30.3, 21.1. One wonders if they got the correct product... $\endgroup$ – orthocresol May 31 at 23:26

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