13C nuclear magnetic resonance spectra. Part 9. Strain effects on 13C chemical shifts of triamantane

Abstract

The 13C n.m.r. spectrum of triamantane (3) observed at 22.64 and 62.8 M H z is assigned using selective lH decoupling. Internal strain causing geometrical distortions at the quaternary carbon leads to a non-additive downfield shift of its signal.IN the course of our investigations on the chemical and spectroscopic properties of substituted and unsubstituted diamondoid hydrocarbons we have made a detailed l3C n.m.r. study of triamantane (3). Triamantane is a C1,H,, hydrocarbon composed of three fused adamantane subunits and has Czu symmetry. Thus the molecule shows eight different types of carbon sites.

Isolation and Structural Proof of the Large Diamond Molecule, Cyclohexamantane (C26H30)

“…[22] The 1 H-decoupled 13 C NMR spectrum of cyclohexamantane ( Figure 5 a) shows three of the expected four signals with the signal for the two equivalent quaternary carbon atoms (atoms 11 and 12; Figure 5 This corresponds with the value of d = 38.6 ppm reported for the structurally related triamantane. [23] Similarly, the CH resonance at d = 37.8 ppm can be assigned to the twelve equivalent CH carbon atoms (atoms 1, 3,5,7,9,14,16,18,20,22,24, and 25; Figure 5 c) and that at d = 47.3 ppm to the six equivalent CH carbon atoms (atoms 2, 6, 10, 13, 17, 21; Figure 5 c) on the basis of the similarities in chemical environment with carbon atom 2 (d = 46.9 ppm) and atom 3 (d = 38.1 ppm) in triamantane. [23] The 1 H NMR spectrum ( Figure 5 c) is characterized by three second-order multiplets (indicating the presence of long-range couplings), which could be assigned on the basis of integration and homonuclear decoupling experiments.…”

“…[23] Similarly, the CH resonance at d = 37.8 ppm can be assigned to the twelve equivalent CH carbon atoms (atoms 1, 3,5,7,9,14,16,18,20,22,24, and 25; Figure 5 c) and that at d = 47.3 ppm to the six equivalent CH carbon atoms (atoms 2, 6, 10, 13, 17, 21; Figure 5 c) on the basis of the similarities in chemical environment with carbon atom 2 (d = 46.9 ppm) and atom 3 (d = 38.1 ppm) in triamantane. [23] The 1 H NMR spectrum ( Figure 5 c) is characterized by three second-order multiplets (indicating the presence of long-range couplings), which could be assigned on the basis of integration and homonuclear decoupling experiments. Thus, the multiplet at d = 1.19 ppm is assigned to six methine hydrogen atoms (associated with carbon atoms 2, 6, 10, 13, 17, and 21), that at d = 1.59 ppm to twelve methine hydrogens (associated with carbon atoms 1, 3, 5, 7, 9, 14, 16, 18, 20, 22, 24, and 25), and that at d = 1.712 ppm to the twelve methylene hydrogens (geminal on the carbon atoms 4, 8, 15, 19, 23, and 26).…”

NMR spectral properties of the tetramantanes – nanometer‐sized diamondoids

“…[22,[37][38][39] Triamantane remains rare and therefore so are its NMR reports. [23,24,40] Tetramantanes occupy a position at the interface of organic chemistry and materials science. They cannot be synthesized by the carbocation methods, [41] so effective for the lower diamondoids.…”

“…1, Table 1. [23][24][25] Nuclear magnetic resonance properties of adamantane, and its derivatives, have been extensively studied [27] since Schleyer discovered high-yielding carbocation methods for lower diamondoid synthesis in 1957. [28] These studies have aided in the development of methods for describing and predicting substituent effects, in both 13 C NMR [29] and 1 H NMR, [30,31] as well as through-space effects, especially in three-dimensional systems.…”

“…[24] Dheu et al, 1979, described difficulties in developing methods for calculating 13 C NMR chemical shifts of triamantane based on analyses of adamantane and diamantane data, but were able to provide a useful empirical method. [23] The diamond-lattice structure of the [20] discussed in the succeeding text. All of these structural features provide important keys for deciphering 13 C and 1 H spectra of the tetramantanes and larger diamond molecules.…”