Trans conformation lattice direction

The lattice moduli of elasticity of poly(ethylene) are quite high since a deformation can only result from a valence angle deformation because of the 2i -trans conformation in the chain direction. On the other hand, it-poly(propylene), poly(oxymethylene), and poly(oxyethylene) occur in helix conformations. Here, deformation occurs as a result of rotation about the valence angles. Consequently, the lattice moduli of elasticity of helixforming polymers are smaller than those of polymers in the diW-trans conformation, i.e., their compliance (extensibility) is higher. 

Polarized infrared external reflection spectroscopy (PIERS) has been very useful in determining the structural details of these SAMs (11,15,20,21). PIERS results show that SAMs of alkanethiolates on gold are nearly analogs of two-dimensional crystalline alkanes. The alkane chains are predominantiy in a trans zig-zag conformation the few gauche conformations are concentrated near the ends of the chains (15,18,23). The alkane chains are tilted 26° relative to the surface normal. This tilt, which allows the chains to be close-packed, is a direct result of the lattice spacing of the sulfur atoms. 

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