Terminal alkynes as a position abstraction tool: Determination of the molecular parameters by semiempirical method

Mechanosynthesis is the fabrication of atomically precise structures by formation of covalent chemical bonds with positional control of mechanical forces. A mechanosynthetic tool should have a chemically active tooltip and a chemically inert handle to which the tooltip is covalently bonded (Temelso, 2006). The suitable molecules for hydrogen abstraction tooltip include the propargyl or ethynyl radical containing two carbon atoms triple bonded together (Drexler, 1992). The unreactive regions of these molecules serve as a handle or attachment point. Hence the terminal alkynes can be used to abstract hydrogen in the production of nano materials (Musgrave et.al. 1991, Srinivasakannan, 2008). Semi-empirical methods serve as a tool in modelling and understanding the properties of molecular systems. In the present work, the structure of four terminal alkynes are optimized by AM1, PM3 & PM7 methods using MOPAC2012 (Stewart, 2013), with the available crystallographic data as the starting geometry. Calculated frequencies are compared with the FTIR spectrum to validate the results. Molecular parameters such as E_HOMO, E_LUMO, the energy gap (ΔE), hardness (η)