Hans-Dieter Beckhaus

[7H]Benzanthrone, a catalyst for the transfer hydrogenation of C60 and C70 by 9,10-dihydroanthracene

[7H]Benzanthrene 2 was used as a catalyst for the transfer hydrogenation of C60 and C70 by 9,10-dihydroanthracene 1. The catalyst allowed milder reaction conditions (250 °C) than the non catalyzed procedure did (350 °C).2 The reaction products identified by EI-MS were C60H36, C60H44 and C70H36 thus a higher degree of hydrogenation could be reached in the case of C60. The method is also suitable for deuteration. A structure proposal for C70H36 and its ΔHf(g) from molecular mechanics calculations are presented.

Anwendung von kraftfeldrechnungen. VI. Verbrennungsenthalpie und bildungsenthalpie von 4-carbomethoxy-homocuban und homocuban-4-carbonsäure — ein testfall zur berechnung von bildungsenthalpien nach dem kraftfeldverfahren

Abstract The heats of combustion of the title compounds were measured by oxygen-bomb combustion calorimetry, using an aneroid isoperibolic microcalorimeter, with the following results: Δ H 0 c (1) 1a = −1431.6 (±1.2); Δ H 0 c (c) 1b = −1263.1(±0.9) kcal mol −1 . The heat of vaporisation of 1a was determined from its vapour pressure, which was measured by GC analysis, with the result Δ H v = 19.1(±0.4) kcal mol −1 . The experimental heats of formation Δ H 0 f (g) and strain enthalpies H s of 1a and 1b ( H s = 117 kcal mol −1 ) are in excellent agreement with results of force field calculations with Allingers MM2 force field ( H s of 1c = 118 kcal mol −1 ). This force field recommends itself, therefore, for the computation of thermodynamic data of polycyclic small ring compounds.

Geminale Substituenteneffekte. Teil 9. Standardbildungsenthalpien und spannungsfreie Inkremente verzweigter Ester und Ether

Zusammenfassung Die Standardverbrennungsenthalpien ΔcH0(liq.). der verzweigten Ester 1, 2 und Ether 3 wurden kalorimetrisch gemessen. Verdampfungsenthalpien ΔvH0 von 1–3 wurden aus der Temperaturabhangigkeit ihrer Dampfdrucke bestimmt, die mit einer Uberfuhrungsmethode gemessen wurden. Daraus ergaben sich die folgenden Resultate: ΔfH0(liq.), ΔvH0 fur 1a: −556,1 ± 1,6, 44,39 ± 0,16; 1b: −587,4 ± 1,6, 44,49 ± 0,39; 1c: −609,5 ± 1,2, 50,57 ± 0,51; 1d: −614,7 ± 1,5, 48,39 ± 0,18; 1e: −616,4 ± 1,0, 50,39 ± 0,34; 2a: −, 51,73 ± 0,23; 2b: −605,7 ± 2,7, 60,04 ± 0,63; 2c: −554,5 ± 1,3, −; 2d: −581,8 ± 1,5, 42,81 ± 0,34; 2e: −624,78 ± 0,98, 50,84 ± 0,57; 3a: −409,1 ± 2,0, 40,94 ± 0,30; 3b: −428,34 ± 0,90, 46,14 ± 0,25, 3c: −406,7 ± 1,5, 44,90 ± 0,50; 3d: −, 53,13 ± 0,19 kJ mol−1. Aus ΔfH0(gas) von 1–3 und kritisch ausgewahlten Literaturdaten wurden neue Werte fur Gruppeninkremente zur Berechnung der Bildungsenthalpien von Estern CO2[2C] −327,05, CH3[CO2] −42,05, CH2[CO2, C] −17,40, CH[CO2, 2C] −7,40, C[CO2, 3C] 4,51, CH03[O] −42,05, CH02[O, C] −33,76, CH0[O, 2C] −31,30, C0[O, 3C] −20,20 und Ethern O[2C] −99,23, CH3[O] −42,05, CH2[O, C] −33,06, CH[O, 2C] −25,64, C[O, 3C] −18,16, Ph[O] 72,02 kJ mol−1 bestimmt.

Geminale Substituenteneffekte Teil 5. Standardbildungsenthalpien von alkylsubstituierten Malonsa¨ure-und α-Aminocarbonsa¨ureestern

Abstract The title compounds 1a–1k were prepared in high purity. Δ H ° c (1) of 1 was measured using an isoperibolic calorimeter Δ H vap of 1 was obtained from the temperature function of the vapour pressure measured in a flow system. The following heats of formation have been obtained in the liquid phase and the gas phase: Δ H ° f (1) and Δ H ° f (g) for 1a −191.13 ± 0.15, −176.35±0.24; 1b −197.50±0.13, −183.69±0.21; 1c −205.17±0.10, −191.86±0.21; 1d −235.8±1.0, −220.3±1.0; 1e −133.94±0.33, − 123.35±0.34; 1f −135.48±0.25, −125.62±0.25; 1g −99.03±0.16, −88.53±0.19; 1h −108.68±0.10, −97.31±0.23; 1i −105.33±0.18, −94.26±0.32; 1j −119.88±0.18, −108.±0.31; 1k −299.30±0.25, −280.37±0.30 kcal mol −1 . The values of the excess destabilization or stabilization energy caused by the geminal substituents is discussed in relation to the branching at the central C atom.

Thermolabile kohlenwasserstoffe. XXVI. Bildungsenthalpie von 1,1,2,2-tetra-tert-butylethan☆

Abstract The title compound ( 1 ) was prepared in high purity by reducing 3,3-dibromo-2,2,4,4-tetra-methylpentane ( 2 ) with magnesium in the last step. The heat of combustion, Δ H 0 c (c), of 1 was measured using an aneroid isoperibol microcalorimeter and the heat of sublimation, Δ H sub , was obtained from the vapour pressure (35–93°C) measured in a flow system. The results: Δ H 0 c (c) = −2913.3(±0.9), Δ H 0 f (c) = −77.6(±0.9) and Δ H 0 f (g) = −59.9(±0.9) kcal mol −1 lead to an outstandingly high value for the excess strain enthalpy ( H s = 66.3 kcal mol −1 ) revealing strong van der Waals repulsions in this highly crowded alkane.

Application of force field calculations—III: Conformational isomerism and dynamic gearing in ethanes with many alkyl substituents. EFF calculations and dynamic NMR measurements

Abstract Force-field calculations and dynamic NMR measurements of symmetrical 1,2-dialkyl-1,1,2,2-tetramethylethanes where the alkyl group is methyl, ethyl, isobutyl, neopentyl, isopropyl, cyclohexyl, or t-butyl are reported. There is usually slightly less than one third of the population in the anti-conformation, slightly more than two thirds in gauche conformations but the t-butyl compound adopts only the anti-conformation. Barriers to rotation vary markedly between 8.1 and 13.8kcal/mol, being lower for secondary alkyl groups than for primary alkyl groups. Calculations suggest that rotation about the central bond and rotation of the secondary alkyl group, by taking place in a concerted fashion, produce several rotational itineraries of similar energies. The low barrier is thus due to a favourable entropy effect.

Thermolabile kohlenwasserstoffe. XVII. Verbrennungsenthalpie und bildungsenthalpie von zehn sym.-tetraalkyl-1,2-diarylethanen

Abstract The title compounds, 1a–1k , were prepared in high purity and the newly synthesized homologues, 1c–1g , were characterized by their NMR and mass spectra. Δ H 0 c (c) of 1 was measured using an isoperibolic calorimeter and Δ H m was obtained using a DSC calorimeter. Δ H sub of 1a was obtained from the temperature function of the vapour pressure measured in a flow system. These data combined with the Δ H v values of 1b–1k estimated by a group increment procedure provide the following results: Δ H 0 f (c), Δ H 0 f (g) and H s (kcal mole −1 ) for 1a = −9.40 (±0.72), 13.70 (±0.8), 10.5; 1b = −72.02 (±0.64), −33.3, 19.7; 1c = −104.34 (±1.15), −60.6, 27.1; 1d = −80.72 (±0.31), −40.6, 32.9; 1e = −97.23 (±0.83), −53.6, 30.2; 1f = −98.23 (±1.45), −50.8, 43.2; 1g = −136.54 (±0.53), −83.8, 30.7; 1h = −7.17 (±0.24), 26.6, 24.2; 1i = −25.54 (±0.38), 10.4, 18.3; 1k = −25.08 (±0.56), 16.6, 45.0. The outstandingly high values of the excess strain enthalpy ( H s ) reveal strong van der Waals repulsions in these highly crowded alkylbenzenes.

Geminale substituenteneffekte: Teil I. Thermochemie von 1-nitro-, 2-nitro-, 2,2-dinitro-und 2-cyano-2-nitroadamantan

Abstract The heats of combustion of 1-nitroadamantane ( 1 ), 2-nitroadamantane ( 2 ), 2,2-di-nitroadamantane ( 3 ) and 2-cyano-2-nitroadamantane ( 4 ) were measured by combustion calorimetry, and the heats of sublimation were derived from the temperature dependence of the vapour pressure measured in a flow system. The results for Δ H XXX c (c) and Δ H Sub (in kJ mol −1 , standard deviation in parentheses) are: 1 , −5824.1 (±2.2) and 63.6 (±1.0); 2 , −5841.0 (±2.2) and 58.0 (±2.3); 3 , −5685.2 (±1.0) and 96.4 (±1.4); 4 , −6238.4 (±1.5) and 70.0 (±1.9). A comparison of the resulting heats of formation Δ H XXX f (g) (in kJ mol −1 , standard deviation in parentheses) for 1 = −191.1 (± 2.4), 2 = −179.8 (±3.2), 3 = −154.3 (±1.7) and 4 = −21.0 (±2.5) reveals a destabilizing interaction of the geminal substituents in 3 and 4 amounting to 59 kJ mol −1 (nitro/nitro) and 33 kJ mol −1 (nitro/cyano) respectively.

Are α-centered peptide radicals stabilized by a capto-dative effect?

The kinetics of the thermal C-C-cleavage reaction of the dimer of sarcosme anhydride 5 has been investigated between 295 and 333 °C in mesitytene. From the temperature dependence and from the release of strain on dissociation the cyclic a-peptide radical 6 was calculated to have a radical stabilization enthalpy (RSE) of-6.3 ± 1.3 kcal / tool thus indicating the absence of a synergistic capto-dative effect.

The dimer of 2-methyl-1,1-diphenylpropyl radicals and its reactivity

Abstract The title radicals dimerize to an α,p-dimer 2 and not to an α,α-dimer 3 as previously 8) assumed. The structure of the dimers of t-benzhydryl radicals Ph 2 ·R in general is strongly dependent on the bulkiness of the R group.