P.v.R. Schleyer

Self‐consistent molecular orbital methods. XVII. Geometries and binding energies of second‐row molecules. A comparison of three basis sets

Three basis sets (minimal s–p, extended s–p, and minimal s–p with d functions on second row atoms) are used to calculate geometries and binding energies of 24 molecules containing second row atoms. d functions are found to be essential in the description of both properties for hypervalent molecules and to be important in the calculations of two‐heavy‐atom bond lengths even for molecules of normal valence.

Rearrangements in the adamantane series : Hydride shifts of the 2-(1-adamantyl)-2-propyl cation

Abstract When subjected to ordinary Koch-Haaf carboxylation conditions the tertiary alcohol, 2-(1-adamantyl)-2-propanol (4) yields only the rearranged carboxylic acid, 3-isopropyl-1-adamantane carboxylic acid (5). Mechanistic evidence is presented which indicates that the rearrangement proceeds via intermolecular hydride shifts. A variety of synthetic approaches to the unrearranged 2-(1-adamantyl)-2-methylpropionic acid (1) are described, and the successful preparation of 1 by the Koch-Haaf reaction of 4 under high dilution conditions is reported. The latter experiment confirms the role of intermolecular hydride shifts in the rearrangement of the 2-(1-adamantyl)-2-propyl cation (26) to the 3-isopropyl-1-adamantyl cation (30).

Homoadamantane. II Analysis of the NMR Spectrum of Homoadamantane

Abstract Due to a fortuitous coincidence of chemical shifts, the nmr spectra of diamondoid hydrocarbons are often exceedingly simple. At 60 MHz the spectrum of adamantane consists of superimposed bands due to the two types of protons present2 A field strength corresponding to 220 MHz3 is needed (Fig. 1A) to cleanly separate bridgehead (δ = 1.87 ppm) and methylene (1.74 ppm) signals. The three kinds of protons in diamantane have even smaller chemical shift differences, and only a single, relatively sharp peak (1.68 ppra) at 100 MHz is seen in the nmr spectrum of this molecule. 4 Noradamantane (II)5 possesses five different types of hydrogens, but even the 220 MHz spectrum (Fig. 1B) shows only three distinct bands: the two broad bridgehead singlets (2.40 and 2.10 ppm) and the multiplet near 1.6 ppm due to the three types of methylene protons. In striking contrast to this behavior, the nmr spectrum of homoadamantane (III) (Fig. 1C, 2A) is unexpectedly complex. In this communication we report the analysis of ...

The mechanism of pyrolysis of polycycloalkyl sulfonates : The homo-retroene reaction in the noradamantane, adamantane and diamantane series

Abstract The minor product, 4-protoadamantene ( 5 ), from the gas phase pyrolysis of 2-adamantyl mesylate ( 3 ) was shown by labelling experiments not to arise from the major product, 2,4-dehydroadamantane ( 4 ), but rather by a concerted process (homo-retroene reaction). In the formation of 4 , 1,3-elimination is favored by at least a 92:8 margin over a competitive route involving α-elimination to a carbene and then C-H insertion. Equatorial and axial 2-noradamantyl mesylates pyrolyze to give predominantly 4 -brendene ( 11 ) and triaxane ( 12 ), respectively, as required by concerted 1,3-eliminations, and not by an ion pair mechanism. The cross-over product appears in each case to result from the epimerizarion of the starting material by a wall-catalyzed process. In agreement with the results of the noradamantyl substrates, pyrolysis of 3-diamantyl mesylate ( 16 ) gave results which suggest that product stability helps to determine the course of the reaction. The products with the least amount of strain were obtained, namely 3,5-dehydrodiamantane ( 17 ) and pentacyclo[8.3.1.0 2,8 .0 4,13 .0 7,12 ]tetradec-5-ene ( 19 , protodiamantene). The ease of separation of the cyclopropanic and olefinic products makes these reactions synthetically useful.