A comparison of relevant properties of selected pyranosyl-RNA and homo-DNA duplexes offers an opportunity for testing the thesis of the predominant role of inter-strand base stacking in oligonucleotide systems with large backbone inclination. Missing base sequences were prepd. and tested. It was found that the sequence dependence of duplex stability in the two pairing systems was, without exception, of opposite directionality. The phenomenon of a quasi-enantio-morphism in the CD spectra of duplexes of a given base sequence in the two systems was also obsd., even though the sense of chirality of the corresponding sugar units in both systems was the same. It is concluded that quasi-linear oligonucleotide systems with strongly inclined backbones represent promising objects of study for detecting and analyzing previously unknown structure-property relationships in nucleic acids. [on SciFinder (R)]