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Alkyl Silane - Conventional Surface Bonding
Aliphatic, fluorinated aliphatic or substituted aromatic hydrocarbon substituents are the hydrophobic entities which enable silanes to induce surface hydrophobicity. The organic substitution of the silane must be non-polar. The hydrophobic effect of the organic substitution can be related to the free energy of transfer of hydrocarbon molecules from an aqueous phase to a homogeneous hydrocarbon phase. A successful hydrophobic coating must eliminate or mitigate hydrogen bonding and shield polar surfaces from interaction with water by creating a non-polar interphase. Although silane and silicone derived coatings are in general the most hydrophobic, they maintain a high degree of permeability to water vapor. This allows coatings to breathe and reduce deterioration at the coating interface associated with entrapped water. Since ions are not transported through non-polar silane and silicone coatings, they offer protection to composite structures ranging from pigmented coatings to rebar reinforced concrete. A selection guide for hydrophobic silanes can be found on pages 22-31 of the Hydrophobicity, Hydrophilicity and Silane Surface Modification brochure.
Atomic layer deposition (ALD) is a chemically self-limiting deposition technique that is based on the sequential use of a gaseous chemical process. A thin film (as fine as -0.1 Å per cycle) results from repeating the deposition sequence as many times as needed to reach a certain thickness. The major characteristic of the films is the resulting conformality and the controlled deposition manner. Precursor selection is key in ALD processes, namely finding molecules which will have enough reactivity to produce the desired films yet are stable enough to be handled and safely delivered to the reaction chamber.
Trimethylsilyl Blocking Agent
Used as a protecting group for reactive hydrogens in alcohols, amines, thiols, and carboxylic acids. Organosilanes are hydrogen-like, can be introduced in high yield, and can be removed under selective conditions. They are stable over a wide range of reaction conditions and can be removed in the presence of other functional groups, including other protecting groups. The tolerance of silylated alcohols to chemical transformations summary is presented in Table 1 of the Silicon-Based Blocking Agents brochure.
Silane Cross-Coupling Agent
The cross-coupling reaction is a highly useful methodology for the formation of carbon-carbon bonds. It involves two reagents, with one typically being a suitable organometallic reagent - the nucleophile - and the other a suitable organic substrate, normally an unsaturated halide, tosylate or similar - the electrophile.
Hexamethyldisilazane; HMDS; HMDZ; Bis(trimethylsilyl)amine
EINECS Number: 213-668-5
Alternative Name: HMDS
Specific Gravity: 0.7742
Flashpoint: 12°C (54°F)
HMIS Key: 2-4-1-X
Hydrolytic Sensitivity: 7: reacts slowly with moisture/water
Refractive Index: 1.4080
Application: Review of synthetic utility.1
Review on organosilane protecting groups.2
Converts acid chlorides and alcohols to amines in a three-component reaction.3
Reacts with formamide and ketones to form pyrimidines.4
Lithium reagent reacts w/ aryl chlorides or bromides to provide primary anilines.5
Used to convert ketones to ?-aminophosphonates.6
Reference: 1. Handbook of Reagents for Organic Synthesis, Reagents for Silicon-Mediated Organic Synthesis, Fuchs, P. L. Ed., John Wiley and Sons, Ltd., 2011, p. 317-319.
2. Larson, G. L. “Silicon-Based Blocking Agents” Gelest, Inc. 2014.
3. Li, H.-H. et al. Eur. J. Org. Chem. 2008, 3623.
4. Tyagarajan, S.; Chakravarty, P. K. Tetrahedron Lett. 2005, 46, 7889.
5. Lee, S.; Jorgensen, M.; Hartwig, J. F. Org. Lett. 2001, 3, 2729.
6. Heo, Y. et al. Tetrahedron Lett. 2012, 53, 3897.
Fieser: F&F: Vol. 1, p 427; Vol. 2, p 159; Vol. 5, p 323; Vol. 6, p 273; Vol. 7, p 167; Vol. 8, p 29; Vol. 9, p 234; Vol. 11, p 38; Vol. 12, p 239; Vol. 13, p 141; Vol. 14, p 300.
Additional Properties: 325Ea, reaction w/SiO2 surface: 17.6 kcal/moleSpecific wetting surface: 485 m2/g?Hcomb: 6,052 kcal/mole?Hvap: 8.3 kcal moleDipole moment: 0.37 debyeSurface tension: 18.2 mN/mVersatile silylation reagent; creates hydrophobic surfaces