.. as it provided a more efficient method for adamantane production. Schleyer was able to increase the output of his adamantane synthesis to a 30% and 40% yield by exposing the tetrahydrodicyclopentadiene to an AlCl3-HCl mixture under 40 atms. of pressure of hydrogen and HF-BF3 catalyst respectively.7 When Schleyer focused his procedure on the retrieval of adamantane, he found that the synthesis was bountiful with the starting reactant dicyclopentadiene which is a common compound.3 Research into the enigmatic compound could then proceeded full force from this point on to examine the compound to its every minute detail. What they found confirmed their previous assertions that adamantane was unlike any carbohydrate known to man.
That carbohydrate was found to be a three fused chairs of cyclohexane rings bound only to hydrogen atoms. The crystallized structure of adamantane was studied in depth by X-ray diffraction. An X-ray diffraction pattern is created through the interaction of photons emitted from an excited metal atom with the crystal form of a compound. The photon either misses the crystal atoms or is deflected by the atom. Most photons miss the atoms, but those deflected do so in a regular pattern because of the repetitious nature of crystals.
That pattern may be recorded through the use of a strip of photographic film or a two-dimensional array detector to provide a hard copy of the deflection pattern.8 Thus the crystalline lattice type, distance between atoms, and number of atoms per unit cell may be found by analysis of the diffraction pattern. The crystal orientation is a face centered cubic lattice that was completely separate from all known carbohydrate crystal orientation.6 Face centered cubic means that there are atoms centered at the faces of the cube as well as at the corners. Adamantane was derived to have a tetragonal space group with four molecules per unit cell, and the vector quantities a = 6.60A and c = 8.81A.7 The carbon bond lengths and angles were stereotypically sound as they were measured to be 1.54 0.01A and 109.5 1.5o respectively.6 This data showed proof that adamantane was a stable compound, but how stable they did not know until the physical qualities were determined. The melting point was determined by sealed tube, and was found to be 269oC which is the melting point for adamantane exposed to the atmosphere as well as the highest melting point for a carbohydrate.9 It is unusual for such an occurrence, but adamantane has no end to its surprises. The exact boiling point of adamantane is impossible to be determined for it is incapable of being reached except by mixture with other carbohydrates at which time the boiling point is 190oC. It is this property that allowed adamantane to be discovered by fractionalization.6 The enigmatic nature of adamantane is reinforced by the fact that it has such a high melting and boiling point, yet it remains true that adamantane will sublime at room temperature and atmospheric pressure.
Now that adamantanes crysatlline structure is known along with the physical properties, what remains is for technology to fill in the blanks as far as molecular interactions of the compound. Adamantane was subjected to NMR and IR(Fig 1,2) Each test produced results that were unique for any carbohydrate upon which the same conditions were exerted.5 The most probable reason for such unique results is the symmetrical nature of adamantane. In fact, adamantane has a symmetry number of twelve which is unheard of in a carbohydrate. This means that throughout the structure there exists a combination of planes and axes about which adamantane is symmetrical or identical that totals twelve. Many compounds, organic and inorganic, are symmetrical in one or two dimensions, but few are symmetrical in three dimensions as adamantane is. NMR uses the magnetic nature of atom nuclei to its advantage. By surrounding a compound in a magnetic field, the nuclei become vulnerable to excitation by radiation in the radiofrequency range.
The radiofrequency that the nuclei absorb is dependent upon the environment the nuclei are exposed to as far as the neighboring nuclei and those the nuclei are bonded to.10 In this case, a proton NMR showed adamantane as only a sharp doublet with a spacing of 0.95 ppm.(Fig 1) The symmetry of adamantane is perfectly supported by these NMR results because only a doublet means that all of the protons are identical in nature. This shows that each proton in the structure of adamantane is sharing each of the electrons equally creating a strong dependence of resonance by all protons.6 The singularity in the NMR result becomes an important diagnostic tool for determination of the purity of an adamantane perspective. Any substitution anywhere on the ring would unbalance resonance of the compound that would be picked up by the NMR in the form of another series of peaks indicating an adamantane derivative as long as the doublet remains present. IR results are much the same as those of NMR in that adamantane itself gives a clear result while any impurity clouds those results. Specifically, adamantane gives a major doublet in the region of 2926 cm-1 with a 0.8983 transmittance, and other peaks shown on Figure 2. This means that around the adamantane compound exists methyl groups that are similar in nature and surrounding environment.
Consequently, all bonds absorb the same wavelengths that suggests identical motion of each of the bonds whether that be stretching, scissoring, or other. Any variance in a functional group would result in the absorbance wavelength to change. Therefore, an increase in the number of peaks and a decrease in intensity of the existing peaks would occur because the change in bonding pattern would limit or expand the possible motions of the bonds. Each bond-motion type absorbs a different wavelength in the IR, so any change in the types changes the absorbances. IR translates the amount transmitted per wavelength to an electrical signal that is interpreted through fourier transform to an IR spectrogram.10 Absorbance is the inverse of transmittance, so any change in absorbance changes the transmittance and the ending spectrogram values.
Since adamantane is so symmetrical and stable, it becomes the perfect basis for many studies and research. In fact the universality of adamantane is so great that it is capable of being used for: structure reactivity relationships, development of empirical force field methods, orientation disorder probe model, and structure basis for drugs.5 The possibilities are endless for adamantane and its uses simply because of its simplicity in nature and structure allow for a structure that is one of the most unique and strong in nature. Bibliography 1. M. Shen, H.F. Schaeffer III, C.
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