The present invention describes novel compounds and methods for capping reactive groups on support and during multistep synthesis. These new capping reagents are also useful for high quality synthesis on solid supports and surfaces used as microarrays, biosensors, or in general as biochips. The compounds are also useful for controlling surface density of reactive groups on a support. The compounds may also be used to modify the hydrophilic/hydrophobic characteristics of a surface or a molecule. The compounds have functional utility in various applications in the fields of genomics, proteomics, diagnostics and medicine.