Structure, stability, cooperativity and molecular packing of two major backbone forms: 3(10)-helix and beta-strand are investigated. Long models HCO-(Xxx)(n)-NH2 Xxx = Gly and (L-)Ala, n <= 34, are studied at two levels of theory including the effect of dispersion forces. Structure and folding preferences are established, the length modulated cooperativity and side-chain determined fold compactness is quantified. By monitoring Delta G(beta ->alpha)(o) a rather than the electronic energy, Delta E-beta ->alpha, it appears that Ala is a much better helix forming residue than Gly. The achiral Gly forms a more compact 3(10)-helix than any chiral amino acid residue probed here for L-Ala. (C) 2013 Elsevier B. V. All rights reserved.