A new class of carbon 1D structures with symmetry of rod groups P6₁ and P3₁ – laterally-extended expanded nanohelicenes (NHs) with zigzag edge morphology – has been thoroughly investigated in the DFT framework. It is shown that these compounds can be divided into two groups, with each group having its distinct properties. The spiral ribbons of NHs of the first and second groups have odd and even numbers of carbon hexagons across, respectively. The first group members are semiconductors and their electronic band gap strongly depends on the uniaxial strain. Expanding the “shaft” (the inner hollow region in a NH spiral) results in a smooth decrease of the electronic band gap. If the outer edge of a NH includes fewer than seven hexagons, then the NH is diamagnetic. When the edge includes seven or more hexagons, antiferromagnetic ordering appears. The second group consists of NHs which are diamagnetic metals at equilibrium geometry that, however, undergo a phase transition to antiferromagnetic semiconductors under small (about 10%) elastic stretching. The difference between the electronic and magnetic properties of NHs in the first and second groups stems from the difference in their electronic structure and can be explained using group theory.