  The Hydrogen and Fluorine planar armchairs graphene nanoribbons (H and F
AGNRs), subjected to twist deformation within fixed periodic boundary
conditions, eventually morph to a helical conformations are investigated at few
tractable points. Unlike structural properties, no effect of symmetries on
mechanical properties is observed, though passivation does have a significant
effect on mechanical as well as on electrical properties. Hookes law for
severely twisted AGNRs indicates the high elasticity of H-AGNRs whereas the
F-AGNRs shows plasticity after threshold torsional strain. Torsional
stress($E_{\theta}$) is approximated from the variation in total
energy(${\Delta}E$) with square of torsional strain(${\theta}^4 {\Sigma}^4$).
Further, the effect of passivation on the electronic properties of helical
conformations with different torsional strain is decisive in metal-to-semimetal
and semimetal-to-metal transition. The band gap response of narrow GNRs N=6, 7
and 8, within a fixed cell under sever twisting arranged itself in two group as
(i) monotonously increasing for q=0,2 and (ii) decreasing for q=1, here
q=mod(N,3) in effective strain space (${\theta}^2 {\Sigma}^2$). This trend has
also been observed for Fluorine passivated AGNRs, though band gap of N=7
F-AGNRs drops from 0.95eV to 0.05eV at extreme torsional strain forming Dirac
cone at K allows dissipation less transport for longer wavelength electrons.
