Adamantane isomers

Time (min) Adamantane (%) Isomer Distribution0 (%) Isomer Distribution0 (%) ... 

Find the MM3 enthalpy of formation of 1- and 2-methyladamantane. Use the Rings tool and the adamant option to obtain the base structure of adamantane itself. Use the Build tool to add the methyl group. 1-Adamantane is the more symmetrical structure of the two isomers. 

Chiral separations are concerned with separating molecules that can exist as nonsupetimposable mirror images. Examples of these types of molecules, called enantiomers or optical isomers are illustrated in Figure 1. Although chirahty is often associated with compounds containing a tetrahedral carbon with four different substituents, other atoms, such as phosphoms or sulfur, may also be chiral. In addition, molecules containing a center of asymmetry, such as hexahehcene, tetrasubstituted adamantanes, and substituted aHenes or molecules with hindered rotation, such as some 2,2 disubstituted binaphthyls, may also be chiral. Compounds exhibiting a center of asymmetry are called atropisomers. An extensive review of stereochemistry may be found under Pharmaceuticals, Chiral. 

KorM75 Kornilov, M. Y. Number of structural isomers in the adamantane series. J. Structural Chem. 16 (1975) 466-468. (Translated from Zh. Strukturnoi Khimii 16 (1975) 495-498). 

If 14 or more carbons are present, the product may be diamantane or a substituted diamantane. These reactions are successful because of the high thermodynamic stability of adamantane, diamantane, and similar diamond-like molecules. The most stable of a set of C H isomers (called the stabilomer) will be the end product if the reaction reaches equilibrium. Best yields are obtained by the use of sludge ... 

Depending on the spatial arrangement of the adamantane units, higher polymantanes n > 4) can have several isomers and nonisomeric equivalents. There are three possible tetramantanes, all of which are isomeric. They are depicted in Fig. 2 as iso-, anti-, and skew-tetramantane. Anti- and skew-tetramantanes each possess two quaternary carbon atoms, whereas iso-tetramantane has three. 

Similarly, and in contrast to the behavior of its secondary isomer, 2-adaman-tanol, 1-adamantanol undergoes smooth, quantitative reduction to adamantane in less than an hour at room temperature in dichloromethane solution containing triethylsilane under the catalysis of either free boron trifluoride129 or boron trifluoride etherate (Eq. 13).143... 

Insertion occurs at the respective a-position of the alkyl substituent. Using a 3 1 ratio of CHBr, to substrate. With a trace of l-(2,2-dichloroethoxy)adamantane.d 1- and 4-isomers in a 1.7 1 ratio. + 2,5-bis(dichloromethyl) derivatives (40%). > Insertion into the tertiary CH. 

Scheme I. Examples of tetraphosphorus- or arsenic-based molecules with the adamantane-type core A4B6. Lewis acid base complexes are not shown. Key to superscripts (when no reference is given, consult Ref. 1-6) A unique non-ada-mantane P4(NR) c oso-structure has recently been obtained with R = i-CjH- (1) and has been shown to convert into the thermodynamically more stable adamantane-type isomer upon heating as in P SglS), P4Sg, and P4S10 Ref. 9 in P4S N- (101,- Hn[P404(CH2)2j04in) orAs40(CH2)2 (121,- 05 in (P406)04- S (13) and [P4(NMe)6l04. S (14).

Identical considerations suggest that the stabilities of the three isomers of CSB7H11 will decrease in the order XIII- > XIV- > XV-NlO. So also the C4BeHxo isomers should be less stable in the order XVII- 20, 165), XVTII-, XIX-NIO 14). Brown et al. 14a), at the University of Liverpool, have shown unequivocally that H4C4B0(CH3)e has an adamantane-type structure with sp boron rather than the carborane structure with sp boron. 

The interconversion of possible CioH16 isomers to adamantane, the thermodynamically most stable isomer, is a very complex system. It involves practically thousands of carbocationic intermediates via 1,2-hydride, alkyde shifts. The interconversion possibilities were summarized in a complex map of rearrangement graph ( adamantaneland ).45,46 The adamantane rearrangement is now recognized to be general for polycyclic hydrocarbons with the formula C4 +6H4 +12 (n = 1,2,3). 

This process is called direct a alkylation. Even the formation of ferf-butyladaman-tane was observed in the superacid-catalyzed alkylation of adamantane with isobutylene necessitating a highly crowded, unfavorable tertiary-tertiary interaction. This provides further evidence for the a-alkylation reaction, as adamantylation of isobutylene with any subsequent isomerization does not lead to this isomer. 

Boron tris(triflate) has also been tested in the adamantylation of benzene and toluene with 1-haloadamantanes [Eq. (5.87)] and2-haloadamantanes.232B(OTf)3 is a highly active catalyst to promote the transformation in very short time under mild conditions to yield isomeric aryladamantanes and adamantane byproduct (Table 5.15). Of the isomeric 1-tolyladamantanes, 1-meto-tolyladamantane predominates, whereas the para isomer is the main product of the 2-tolyladamantanes. The ortho isomers were... 

Laali et al.234 have developed a method to the highly selective pura-adamantylation of arenes (toluene, ethylbenzene, anisole) with haloadamantanes (1-chloro- and 1-bromoadamantane, l-bromo-3,5,7-trimethyladamantane) and 1-adamantanol promoted by triflic acid in butylmethylimidazolium triflate [BMIM][OTf] ionic liquid. In contrast to reactions mn in 1,2-dichloroethane, little or no adamantane byproduct was detected in [BMIM][OTf. Furthermore, no isomerization of para-tolyladamantane was observed supporting the intramolecular nature of the formation of meta isomers. In competitive experiments with benzene-toluene mixture (1 1 molar ratio), high substrate selectivities were found (kT/kB = 16-17) irrespective of the alkylating agent. This is in sharp contrast to values about unity measured in 1,2-dichloroethane. 

A general mathematical treatment has recently been developed which enables the construction of a graphical representation of such rearrangements39 . This treatment has been applied to the rearrangement of tetrahydrodicyclopen-tadiene (2) to adamantane (l)40). Assuming that only 1,2-alkyl shifts are allowed and excluding steps which form either primary cations or unreasonably strained isomers, the intermediates which may be involved and the pathways by which they are interconverted are illustrated in Scheme 3 4° . At least 2,897 independent pathways for the conversion of 2 to 1 are possible40). 

Future determinations of the strain energies of the Ci0Hi6 isomers, illustrated in Scheme 3, as well as their corresponding cations (e. g. by calculation) 95) should help clarify the relative ease with which each of the isomers rearranges to adamantane. The true significance of the formal description of the adaman-tane rearrangement (Scheme 3) 4°1 lies, for the moment, in the fact that a rational framework for the discussion of the mechanism of the reaction is established. 

Both of the dehydroadamantane isomers undergo rapid electrophilic additions and may, in certain cases, provide useful syntheses of 2,4- and 1,3-disubstituted adamantanes. These reactions will be discussed in Section V.A. 

Functional group manipulations are equally successful for the preparation of a wide variety of 2-substituted adamantanes. Starting with the methyl ester of 2-adamantane carboxylic acid S7> 2061, 2-t-butyladamantane (71) may be prepared in a manner anlogous to that described above for the synthesis of the bridgehead isomer (Scheme 17) 2M These reactions illustrate the... 

By analogy with adamantane, direct, ionic substitution reactions may be expected to be equally as effective for the synthesis of derivatives of other diamondoid hydrocarbons (e.g. diamantane and triamantane). In these cases, however, a larger number of isomers are possible. Diamantane has one methylene and two nonequivalent bridgehead positions while triamantane has four of each. 

For adamantane itself, statistically corrected tertiary/secondary ratios of 2-6 are commonly observed for free radical initiated hydrogen abstractions 206,268-272) por example, photochlorination of adamantane in CCI4 gives 37 % 1-chlo-roadamantane and 73 % of the secondary isomer 268). Due to the decreased... 

The second route to 2,4-disubstituted adamantanes involves a 7r-route ring closure of substituted bicyclo[3.3.1]nonenes. Thus, lactone 85 28S) rearranges in 50 % sulfuric acid to 4-hydroxy-2-adamantanone (86) via the acylium ion 87 278>. Adamantanone oxime rearranges in 96 % sulfuric acid to 86 (mixture of isomers) in an analogous manner 109h Similarly, the Schmidt reaction of... 

C6o reacts with diazomethane to yield fulleroids [97,99,100,234], Carbene generated from the thermolysis of precursors such as diazirines, sodium trichloroac-etate, cyclopropene, oxadiazole, and tosylhydrazone [60,235] adds onto C6o leading to methanofullerenes [12,15,236], Recently, Akasaka et al. described the photochemical reaction of diazirine with C6o [237], Irradiation of a benzene solution of 2-adamantane-2,3 -[3H]-diazirine 58 and C6o with a high pressure mercury lamp (cutoff <300 nm) at 15°C in a Pyrex tube resulted in the formation of mixture of the isomers 59a and 59b in a ratio of 51/49 (Scheme 24). 

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