Hard and straight: Diamond is the hardest material known, yet polyyne—a molecular rod comprised of CC units—resists longitudinal compression with a Young's Modulus 40 times larger than diamond, whereas [n]staffanes have a Young's Modulus close to that of diamond. Mechanical engineering provides the connection between the point at which a rod buckles under longitudinal load and its cross‐sectional area.

Negative feedback: Auxetic materials are materials that, counterintuitively, become thicker when stretched and thinner when compressed (negative Poisson's ratio). Quantum mechanical computations were used to identify poly[n]prismanes (n=3–6), the first nanomolecular systems that manifest auxetic behavior at the molecular level. The magnitude of the negative Poisson's ratio in these prismanes ranges from 7 to 15 %.

Negative Rückmeldung: Auxetische Materialien sind Materialien, die beim Strecken dicker und beim Zusammendrücken dünner werden (negatives Poisson‐Verhältnis). Quantenmechanische Rechnungen identifizieren die Poly[n]prismane (n=3–6) als erste nanomolekulare Systeme, die auf molekularer Ebene auxetisches Verhalten zeigen. Das negative Poisson‐Verhältnis dieser Prismane liegt zwischen 7 und 15 %.

Geradlinig und hart: Diamant ist das härteste bekannte Material, doch Polyine – stabförmige Moleküle aus CC‐Einheiten – halten einer longitudinalen Stauchung mit einem Young‐Modul stand, der vierzig Mal so groß ist wie der von Diamant; [n]Staffane zeigen einen ähnlichen Young‐Modul wie Diamant. Der Punkt, an dem das Stabmolekül unter longitudinaler Belastung zu knicken beginnt, wurde durch mechanisches Engineering mit dem Stabquerschnitt in Beziehung gebracht.

Ab initio methods were used to calculate the geometry and the charge distribution (natural bond orbital) in end-protonated polyynes. The geometry obtained is practically identical to that of the corresponding anion and the neutral radical. Thus, the geometry is not much dependent on charge dispersal. Moreover, it is shown that regardless of whether the imposed geometry is that of a cumulenic structure which localizes the charge at one end or that of the neutral molecule which localizes the charge at the other end, the same amount of charge is delocalized to the remote end of the protonated molecule regardless of the imposed structure. The same phenomenon is observed also for polyenes. It is interesting to note that regardless of the charge or its absence, as in the case of the radical, the optimal geometry is obtained as the arithmetic sum of the main resonance structures. Thus, it is concluded that, in these cases, the wave function is only weakly coupled to the geometry of the molecule.