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The formation of cyclic duplexes (pairing) of known oxymethylene‐linked self‐complementary U*[o]A(*) dinucleosides contrasts with the absence of pairing of the ethylene‐linked U*[ca]A(*) analogues. The origin of this difference, and the expected association of U*[x]A(*) and A*[x]U(*) dinucleosides with x=CH2, O, or S was analysed. According to this analysis, pairing occurs via constitutionally isomeric Watson–Crick, reverse Watson–Crick, Hoogsteen, or reverse Hoogsteen H‐bonded linear duplexes. Each one of them may give rise to three diastereoisomeric cyclic duplexes, and each one of them can adopt three main conformations. The relative stability of all conformers with x=CH2, O, or S were analysed. U*[x]A(*) dinucleosides with x=CH2 do not form stable cyclic duplexes, dinucleosides with x=O may form cyclic duplexes with a gg‐conformation about the C(4′)C(5′) bond, and dinucleosides with x=S may form cyclic duplexes with a gt‐conformation about this bond. The temperature dependence of the chemical shift of HN(3) of the self‐complementary, oxymethylene‐linked U*[o]A(*) dinucleosides 1–6 in CDCl3 in the concentration range of 0.4–50 mM evidences equilibria between the monoplex, mainly linear duplexes, and higher associates for 3, between the monoplex and cyclic duplexes for 6, and between the monoplex, linear, and cyclic duplexes as well as higher associates for 1, 2, 4, and 5. The self‐complementary, thiomethylene‐linked U*[s]A(*) dinucleosides 27–32 and the sequence isomeric A*[s]U(*) analogues 33–38 were prepared by S‐alkylation of the 6‐(mesyloxymethyl)uridine 12 and the 8‐(bromomethyl)adenosine 22. The required thiolates were prepared in situ from the C(5′)‐acetylthio derivatives 9, 15, 19, and 25. The association in CHCl3 of the thiomethylene‐linked dinucleoside analogues was studied by 1H‐NMR and CD spectroscopy, and by vapour‐pressure osmometric determination of the apparent molecular mass. The U*[s]A(*) alcohols 28, 30, and 31 form cyclic duplexes connected by Watson–Crick H‐bonds, while the fully protected dimers 27 and 29 form mainly linear duplexes and higher associates. The diol 32 forms mainly cyclic duplexes in solution and corrugated ribbons in the solid state. The nucleobases of crystalline 32 form reverse Hoogsteen H‐bonds, and the resulting ribbons are cross‐linked by H‐bonds between HOCH2C(8/I) and N(3/I). Among the A*[s]U(*) dimers, only the C(8/I)‐hydroxymethylated 37 forms (mainly) a cyclic duplex, characterized by reverse Hoogsteen base pairing. The dimers 34–36 form mainly linear duplexes and higher associates. Dimers 34 and particularly 38 gelate CHCl3. Temperature‐dependent CD spectra of 28, 30, 31, and 37 evidence π‐stacking in the cyclic duplexes. Base stacking in the particularly strongly associating diol 32 in CHCl3 solution is evidenced by a melting temperature of ca. 2°.

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The tectonic evolution of the Mont Blanc range with regard to its cooling and exhumation history has been discussed and debated over many years and is still controversial. Recently, several low-temperature thermochronology studies have determined the cooling history of the massif in considerable detail and various tectonic models proposed to explain the young and fast exhumation signal established from these studies. Here we present detailed field data from the wider Mont Blanc area and assess possible exhumation processes in terms of these field constraints. Our observations indicate that none of the major faults or shear zones around the Mont Blanc massif (i.e. Mont Blanc shear zone, Mont Blanc back-thrust, Penninic thrust) was active in Late Neogene times and that young exhumation is therefore not controlled by movements along these structures. We demonstrate that the position of Mont Blanc in the bend of the western Alps plays an important role in its tectonic history and that simple 2D models are insufficient to explain its evolution. Interference between NW-SE compression and orogenparallel extension along the Rhône-Simplon fault system resulted in a complex regional structural pattern, with strike-slip movements on both sides of the Mont Blanc massif. Young brittle faults are predominantly strike slip without significant vertical offset. The young (\2 Ma) rapid exhumation of Mont Blanc is more broadly distributed and cannot be directly linked to discrete faults bounding the massif. The mechanisms driving this recent accelerated exhumation must similarly be of broader scale.