H-Si(111)-terminated surfaces were alkenylated via two routes: Through a novel one-step gas-phase hydrosilylation reaction with short alkynes (C3 to C6) and for comparison via a two-step chlorination and Grignard alkenylation process. All modified surfaces were characterized by static water contact angles and X-ray photoelectron spectroscopy (XPS). Propenyl- A nd butenyl-coated Si(111) surfaces display a significantly higher packing density than conventional C10-C18 alkynederived monolayers, showing the potential of this approach. In addition, propyne chemisorption proceeds via either of two approaches: The standard hydrosilylation at the terminal carbon (lin) at temperatures above 90°C and an unprecedented reaction at the second carbon (iso) at temperatures below 90°C. Molecular modeling revealed that the packing energy of a monolayer bonded at the second carbon is significantly more favorable, which drives iso-attachment, with a dense packing of surface-bound iso-propenyl chains at 40% surface coverage, in line with the experiments at <90°C. The highest density monolayers are obtained at 130°C and show a linear attachment of 1-propenyl chains with 92% surface coverage.