Vicinal silanol groups

Isolated silanol group Vicinal silanol groups Geminal silanol groups... 

The active sites (centers) of silica are mainly the free and bonded silanol groups as shown in Figure 1. Two vicinal silanol groups connected by hydrogen bonds form the bonded hydroxyl groups. In the case of normal-phase liquid chromatography (NPLC), these sites interact with the polar analyte functional group/s. Thus, silica is considered as a polar stationary phase. The properties of a specific silica depend on its surface area and the number of active sites. 

Solid-state Si MAS NMR spectra of MCF-A, APTES-MCF-A and APDMES-MCF-B are shown in Figure 3. The untonctionalised MCF-A, shows what appears to be three distinct peaks, which can be assigned as surface ganinal groups (Q ), surface vicinal silanol groups... 

The NMR-Raman data indicate that in gels three-membered rings are absent at low temperatures. They form at intermediate temperatures primarily on the silica gel surface by condensation reactions involving isolated vicinal silanol groups located on unstrained precursors [32] ... 

Vicinal Literally means close to or nearby and is used in the description of surface silanol groups. As opposed to isolated nonin-teractive silanol groups, vicinal silanols groups are spatially close enough to hydrogen bond with one another ... 

---