Diamantane formation

In Table IV we report the available enthalpies of formation, sublimation, and combustion of methyl-adamantanes, dimethyl-adamantane, trimethyl-adamantane, and tetramethyl-adamantane and compare them with the same properties of adamantane as measured by various investigators [29, 30]. Also reported in Table IV are the same properties for 1-methyI-diamantane, 3-methyI-diamantane, and 4-methyI-diamantane as compared with the diamantane data. 

Adamantane can be transformed to 4-oxahomoadamantane in good yields by bis (trimethylsilyl)peroxide664 and sodium percarbonate665 in the presence of triflic acid. Product formation is explained by C—C cr-bond insertion [Eq. (5.233)]. Diamantane is transformed into isomeric oxahomodiamantanes (C—C insertion) and bridgehead diamantanols (C—H insertion).664... 

The SNl-type transformation of secondary and tertiary alkanols with the help of trichloroacetic acid and hydrazoic acid has also been mentioned in Section I.8.4.2.I. Several azides, e.g. of the adamantane and diamantane series, have been obtained on treatment of the corresponding alcohols with NaNs and sulfuric acid. As expected, this procedure lends itself particularly well to the formation of tertiary azides." Treatment of tertiary carbinols with HN3 and BF3 or other Lewis acids represents another route... 

Disubstituted diamantanes. The tetrahydro derivative (1) of Bisnor-S (2, 123-124 3,7 4, 140) on treatment with neat chlorosulfuric acid (mole ratio 1 5.7) at -15° is converted into 4,9-dichlorodiamantane (2) in 82% isolated yield. The mechanism for formation of (2) is not known, but it does not... 

Absolute determination of AG is the most general method. From the experimentally determined enthalpies of formation of compounds (A// ) relative stabilities can easily be calculated (after consideration of AS, vide infra), but such experimental work requires large quantities (>1 g) of extremely pure material. Also, since the heat of formation of a compound is calculated from the difference of its measured heat of combustion and the heat of combustion of its constituent elements, quantities which can be in the 1000-4000 kcal mole" range, small experimental errors (>0.02%) lead to relatively large errors in AH (10). The measurement of heats of vaporization or of sublimation needed to convert A/f (l) and Af/ (s) to AH (g) are also difficult experimentally (11). Premelting transitions (5i, 12) complicate matters further. As a result, reported experimental values of AH for a given compound may differ by as much as several kilocalories per mole (e.g., adamantane and diamantane, see Table 2). 

Those who do calorimetry are extremely fussy about the purity of their compounds. For the adamantane type of compound, however, it can be extremely difficult to obtain a truly pure sample. Globular hydrocarbons tend to form solid solutions with one another and with many other compounds as well. These compounds are typically purified by chromatography, recrystallization, and sublimation (multiple times). But in spite of best efforts, problems can and occasionally do persist. The heat of combustion of 6 was then redetermined by Claik and co-workers and also duplicated by Good, on a more highly purified sample of diamantane, and they obtained closely similar results. The two heats of combustion were 1942.06 0.60 and 1942.58 0.32kcal/mol, which yielded a weighted value for the heat of formation of-34.54 0.41 kcal/mol. The value shown for the heat of formation of 6 in Table 11.3 (32.60 0.58) was then superceded by 34.54 0.41 kcal/mol, very close to that predicted by MM2 (34.30kcal/mol). ... 

Now if we consider the heat of formation of 4-methyldiamantane (compound 7), we can see that we have simply added a bridghead adamantane-like methyl into a very similar environment in diamantane. Since the methyl group increments are additive in the adamantane case, we would expect that the number should carry over equally well to the 4-methyldiamantane example. And indeed this is found to be trae (Table 11.4). Accordingly, we can now be fairly well convinced that these adamantane/diamantane numbers mentioned are all correct to within the stated experimental errors. 

C—C bond reorganization in confined space is also possible with sp -hybridized carbon-based molecules. Adamantane was confined in DWCNTs forming linear adamantine assanbUes [188]. The annealing of the sp -hybridized nanostructures under vacuum at temperatures higher than 500°C convert the adamantine into carbon chains inside the CNTs however, the introduction of H2 during the annealing step suppressed their formation. Similarly, diamond nanowires formed inside DWCNTs from encapsulated diamantane dicarboxylic acid [189]. 

An aneroid static-bomb combustion calorimeter has been employed to determine the standard enthalpy of formation of a small sample (ca. 20 mg) of bicyclo[3,3,3]nonane (— 36-4g + 0-42 kcal mol ), and a temperature-scanning technique makes use of a commercial gas chromatograph in the measurement of the vapour pressures of several adamantane and diamantane derivatives. Results were converted into heats of sublimation by employing the Clausius-Clapeyron equation doubt is cast on the accuracy of a previously recorded value for diamantane. 

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