Proton magnetic resonance spectra of cubane derivatives. I. Syntheses and spectra of mono- and 1,4-disubstituted cubanes

Abstract

The syntheses of a number of monosubstituted and 1,4-disubstituted cubanes are described, together with the measurement and analysis of their 100-MHz ' H N M R spectra. Typical coupling constants observed are 5.3 Hz (vicinal), 2.5 Hz (four bond), and -0.7 H z (five bond). A simple additivity rule is described whereby chemical shifts in CDCI, can be predicted to within d~0.02 ppm. Both chemical shifts and coupling constants are shown to var.y with substituent electronegativity. The derived correlations allow quick and effective identification of cubane derivatives from their ' H N M R spectra, and also aid in the interpretation of the more complex spectra of less symmetrical cage molecules. ResultsAnalysis of the Spectra. In all mono-or disubstituted cubanes, three geometries of proton spin-spin coupling are possible. Following Cole's designation2Q of cubane substitution patterns, we have termed these couplings oftho (along an edge of the cube), meta (across a face of the cube), and para (along a diagonal of the cube). The 1,4-disubstituted cubanes (I) form Ha Hn I J A B = JORTHO JAA,, JBBT = JMETA J'AB = JPARA an [AB13 spin system and the observed chemical shifts of HA and H B differ by < I ppm, depending upon the substituents X and Y. The monosubstituted cubanes (11) form a much more complex [AB]3C system, and in all the cases we have studied the B and C chemical shifts are very close (less than 0.05 ppm I1 J A W JR,. = JOKTHO J A A '~ JRH', JAC = JMWA J'AH = J i i A n Adifference). Thus their spectra are considerably more difficult to analyze than those of the 1,4-disubstituted cubanes.All spectra were analyzed using the LAOCN321 computer program and the results plotted on a Calcomp Plotter. Approximate values of coupling constants were estimated by first-order analysis of the nearly [AX13 spectra of the substituted 4-methylcubanes. These estimates were varied until the spectra computed from them were similar to the experimental spectra, and then the fit was optimized by iterative calculation. It is impossible to analyze the spectra exactly because of the enormous number of unresolved lines (less than 20 peaks and shoulders can be assigned in the average spectrum). Thus it is necessary to assign the calculated lines to fit under an ex-Edward, Farrell, Langford / Proton Magnetic Resonance Spectra of Cubane Derivatives 133.3' 376.7J " Chemical shifts in Hz at 100 MHz. All samples in CDC13 except as noted. Shifts calculated by eq 1. Same as HA. Hc shift. e OCH3 Unresolved singlet for A and B protons; IYIu d estimated from line width. The reverse assignment Solvent is D2O with TMT as external reference.shift. f CH3 shift. of A and B shifts is also possible. J CH20H shift, Ir R = (cubyl)C02CH3. C(CH3)3 shift. NHC02CH3 shift.Solvent is DZO/NaOD, with TMT as external reference.

The structure of cubane mono and 1,4-dicarboxylic acids in lyotropic liquid crystalline solution

“…Table 1 gives the values obtained and their probable errors. The indirect couplings agree well with those previously reported (12). All spectra were analysed using the nmr program DIPUEA (13).…”

“…The preparation of these cubane derivatives is reported elsewhere and the compounds used here were received as a gift from those authors (12).…”

Cubane derivatives 7. Synthesis and molecular structure of 4-bromo-1-hydroxymethylcubane

“…14 Compound 1 was prepared according to a procedure described earlier. 15 Reduction of ester 1 with lithium aluminum hydride. A.…”

Synthesis and carbon-13 NMR analysis of a series of bridgehead-substituted polycycloalkanes: carbon-13-labeled methyl as the substituent

“…Irradiation of 1-methylbicyclo[2. 1.1]hexan-2-one-7-,3C (25) under the above conditions produced 8c: NMR (CDC13) 1.10 (t, 3 H, J = 125 Hz). l-Methylbicyclo[3.1.1 Jheptane (16, R = CH3).…”