A previously inexplicable difference between the Highland Border Complex, Scotland, and its correlative in Ireland, the Clew Bay Complex, is that rocks of Caradoc–Ashgill age occur only in the former. We reject evidence from supposed chitinozoa for this dichotomy: no sedimentary rocks of proven age younger than Arenig occur in the Highland Border Complex. Consequentially, the stratigraphy must be totally recast, and the ‘exotic terrane model’ replaced by one in which a largely autochthonous Highland Border Complex in stratigraphical continuity with the Dalradian (Grampian terrane), was overridden by the Highland Border ophiolite (Midland Valley terrane). Tectonic models for SE Laurentia are thereby considerably simplified.
Periodate oxidation studies, nuclear magnetic resonance spectra of derivatives, and X-ray crystallographic data have shown that plicatic acid, the major component of the heart\vood extractive of western red cedar (Tltz~ja plicata Donn), is 2,3,6-trihydroxy-7-methoxy-2-hydroxymethyl-4-(3',4'-dihydroxy-5'-methoxyphenyl)-tetralin-3-carbosylic acid. The asymmetric configuration by X-ray data is 2R,3S,4R or its enantiomer, by Cahn-Ingold nomenclature.Analytical and degradation studies described in previous papers (1, 2) provided a partial structure for plicatic acid, the reactive strong acid polyoxyphexlol present in the heartwood of western red cedar. Plicatic acid, now shown to be I , forins a y-lactone, termed plicatin, which also occurs in the heartn ood, although in snlaller quantities. T o assist in the location of the alcoholic lzydroxyls, the oxidation \\it11 sodium periodate of various crystalline methyl ether derivatives of plicatic acid mas examined. The results are sumn~arized in Table I.The usual arsenite (3) technique for determining the periodate cons~~mption, ~vhich involves treatinent of aliquots with sodiuill bicarbonate solution, could not be used. T h e raising of the PI-I by the bicarbonate induced rapid over-oxidation in the aliquot solution, with the forination of yellow and then blue dyes, wllich are presently under investigation.
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