Cubane, Cuneane, and Their Carboxylates: A Calorimetric, Crystallographic, Calculational, and Conceptual Coinvestigation
作者:Maria Victoria Roux、Juan Z. Dávalos、Pilar Jiménez、Rafael Notario、Obis Castaño、James S. Chickos、William Hanshaw、Hui Zhao、Nigam Rath、Joel F. Liebman、Behzad S. Farivar、A. Bashir-Hashemi
DOI:10.1021/jo050471+
日期:2005.7.1
This study is a multinational, multidisciplinary contribution to the thermochemistry of dimethyl1,4-cubanedicarboxylate and the corresponding isomeric, cuneane derivative and provides both structural and thermochemical information regarding the rearrangement of dimethyl 1,4cubanedicarboxylate to dimethyl 2,6-cuneanedicarboxylate. The enthalpies of formation in the condensed phase at T = 298.15 K of dimethyl 1,4-cubanedicarboxylate (dimethyl pentacyclo[4.2.0.0.(2,5)0.(3.8)0(4,7) octane-1,4-dicarboxylate) and dimethyl 2,6-cuneanedicarboxylate (dimethyl pentacyclo[3.3.0.0.(2,4)0.(3,7)0(6,8)]octane-2,6-dicarboxylate) have been determined by combustion calorimetry, Delta H-f degrees(m)(cr)/k.J(.) =232.62 +/- 5.84 and -413.02 +/- 5.16, respectively. The enthalpies of sublimation have been evaluated by combining vaporization enthalpies evaluated by correlation-gas chromatography and fusion enthalpies measured by differential scanning calorimetry and adjusted to T = 298.15 K, Delta H-g(cr)m (298.15 K)/kJ (.) mol(-1) = 117.2 +/- 3.9 and 106.8 +/- 3.0, respectively. Combination of these two enthalpies resulted in Delta H-f degrees(m)(g., 298.15 K)/kJ (.) mol(-1) of -115.4 +/- 7.0 for dimethyl 1,4-cubanedicarboxylate and -306.2 +/- 6.0 for dimethyl 2,6-cuneanedicarboxylate. These measurements, accompanied by quantum chemical calculations, resulted in values of Delta H-f(m)(g, 298.15 K) = 613.0 +/- 9.5 kJ (.) mol(-1) for cubane and 436.4 +/- 8.8 kJ (.) mol(-1) for cuneane. From these enthalpies of formation, strain enthalpies of 681.0 +/- 9.8 and 504.4 +/- 9.1 kJ (.) mol(-1) were calculated for cubane and cuneane by means of isodesmic reactions, respectively. Crystals of dimethyl 2,6-cuneanedicarboxylate are disordered; the substitution pattern and structure have been confirmed by determination of the X-ray crystal structure of the corresponding diacid.