Heats of formation of [2.2]paracyclophane-1-ene and [2.2]paracyclophane-1,9-diene - an experimental study

The enthalpies of formation [Delta(g)] of tricyclo[8.2.2.2(4,7)]hexadeca-1(13),2,4(16),5,7(15),10(14),11-heptaene (2, 1,2-dehydro[2.2]paracyclophane or [2.2]paracyclophane-1-ene) and tricyclo[8.2.2.2(4,7)]hexadeca-1(13),2,4(16),5,7(15),8,10(14),11-octaene (3, 1,2,9,10-dehydro[2.2]paracyclophane or [2.2]paracyclophane-1,9-diene) have been determined by measuring their heats of combustion in a microcalorimeter and their heats of sublimation by the transpiration method. Values of the strain energies (SE) [SE(2) = 34.7 kcal mol(-)(1), SE(3) = 42.0 kcal mol(-)(1)] have been derived from the gas-phase heats of formation and are compared with those from MM3 and PM3 calculations and with the corresponding value SE(1) = 30.1 kcal mol(-)(1) for the parent tricyclo[8.2.2.2(4,7)]hexadeca-1(13),4(16),5,7(15),10(14),11-hexaene (1, [2.2]paracyclophane). The higher strain energies of 2 and 3 (by 4.6 and 11.9 kcal mol(-)(1)) are in accord with the well-known increased reactivities of their aromatic rings as a consequence of their increased bending. As revealed by an X-ray crystal structure analysis, the bending in the monoene 2 corresponds to that of 1 and 3 at one of two bridging corners.     

Stereoisomeric flavor compounds,part LVIII: The use of heptakis(2,3-di-O-methyl-6-O-tert-butyldimethylsilyl)-β-cyclodextrin as a chiral stationary phase in flavor analysis

The characteristics of the new chiral stationary phase heptakis(2,3-di-O-methyl-6-O-tert-butyldimethylsilyl)-β-cyclodextrin are outlined and compared with permethyl- and perethyl-β-cyclodextrins.     

Determination of the atomic charge on sodium in sodium salts by numerical integration — a theoretical investigation

The electron density difference in a NaSCN crystal is set up from the ab initio densities of Na⁺ and SCN^? ions and compared to the experimental counterpart based on X-ray diffraction measurements. Numerical integration over the electron density difference is executed around the Na⁺ ion. The atomic charge (+0.20e) derived in this way is in good agreement with the analogous experimental charge (+0.27e) The low experimental value cannot therefore be taken as an indication for a predominantly non-ionic structure of NaSCN and similar sodium salts     

1H-NMR-spektroskopische konformationsanalyse von halogenierten thymidinabkömmlingen: I. konformation von thymidin, 3',5'-didesoxy-3'-chlor-5'-fluor-thymidin und 3', 5'-didesoxy-3',5'-difluor-thymidin

An improved method is given for determining the conformation of furanoid nucleosides by ¹H-NMR-spectra analysis using halogen-substituted thymidines as examples. The state of the three equilibria - ring-puckering, rotation about the C₄-C₅- bond and about the glycosidic bond - are influenced by the halogen substituents. Compared with thymidine the 3'-chlorine substituent shifts the furanose conformation to conformers, where the 3'-chlorine substituent is equatorial. The 5'-fluorine substituent increases the contribution of the G-G-rotamer and the ratio of syn-conformation. The relationships between the conformers in the pseudo-rotatory cycle and the population of the C_4'-C_5' rotamers are discussed.     

Surface area of papermaking woodpulps used by the British paper industry

The surface area was determined for various papermaking woodpulps: bleached eucalyptus globulus sulphate pulp; bleached eucalyptus grandis sulphate pulp; bleached betula verrucosa sulphate pulp; bleached pine/spruce sulphate pulp; bleached pine/spruce sulphate pulp fines. The method of negative adsorption was used which gives an effective wet surface area. By looking at negative adsorption data more closely, some inference can be made about the morphology of the substrate.Glossary of symbols B (e²/2kT)^1/2 - ¯C concentration of fibre per unit volume of pulp - 1 - ¯¯c - h angle between pore and the axis of the bed in a permeable material - K permeability coefficient - k Boltzmann constant - k ₀ shape factor for pores in a permeable material - n _i concentration of co-ion in the bulk solution - n _i experimentally observed increase in concentration of co-ion in the bulk solution - S surface area - S _t wS - S ₀ surface area per unit volume of permeable material - V _t total volume of solution - V excluded volume - V _s excluded volume accessible to water but not to ions - V _obs experimentally observed excluded volume - w weight of dry fibre - ¯ effective volume of fibres in a permeable pad - surface potential at outer Helmholtz plane     

Amidine als Zwischenprodukte bei Umamidierungsreaktionen. 9. Mitteilung über Umamidierungsreaktionen

Amidines as Intermediates in Transamidation Reactions By loss of water in the presence of p-toluenesulfonic acid/xylole N-aminoalkyllactames form bicyclic amidines. The corresponding N-alkylaminoalkyl-lactames' react to bicyclic amidinium salts or to transamidated products, ring-enlarged by the N-alkylamino residue, respectively (s. Scheme 1). The bicyclic amidines and amidinium salts are partially hydrolyzed by KOH/H₂O to lactames (s. Scheme 2). Which of the two possible isomeric lactames are formed is discussed.     

Final elucidation of the absolute configuration of the signal metabolite hormaomycin

The complete absolute configuration of hormaomycin 1 a has been established by HPLC and HPLC/MS experiments with appropriately derivatized 4-propylprolines, (2S,4S)-6 and (2R,4R)-6, as well as 4-(Z)-propenylprolines, cis-5 and trans-5, and also feeding experiments with enantiomerically pure samples of the deuterium-labeled 3-(2'-nitrocyclopropyl)alanine, (2S)-3,3-[D2]15 and (2S)-2,2'-[D2]15, and 4-(Z)-propenylproline 2',4-[D2]-(2S,4R)-5. The latter five amino acids were prepared for the first time and allowed one to unequivocally assign the hitherto unknown absolute configurations of the last four stereocenters in hormaomycin 1 a. As a bonus, some new information about the biosynthesis of this molecule has also been gathered.     

Transition metal-catalyzed intermolecular [5+2] and [5+2+1] cycloadditions of allenes and vinylcyclopropanes

Initial examples of the intermolecular Rh(I)-catalyzed [5+2] cycloaddition reaction of bifunctional allenes and vinylcyclopropanes are described. The reactions proceed with facility and in yields of up to 99% with a variety of alkyne-, ester-, styrene-, or cyano-substituents on the allene to afford the corresponding cycloadducts. In the presence of CO, the reaction proceeds to an eight-membered ring cycloadduct and its transannularly closed product, providing the first example of a three-component [5+2+1] cycloaddition with allenes.     

Synthesis of Oncinotin-11-one,a Macrocyclic Polyamine Alkaloid from Oncinotis tenuiloba

This paper presents a short synthesis of oncinotin-11-one ( 11 ), a minor alkaloid of Oncinotis tenuiloba (Apocynaceae). Based on a disconnection approach, the spermidine portion of the key intermediate 6 was constructed consecutively by simple N-alkylations starting from ethyl piperidine-2-carboxylate ( 1 ). Treatment of 6 with in situ lithiated 2-[(10-bromodecyl)oxy]tetrahydropyran resulted in the formation of the keto moiety under simultanous deprotection of the lactam N-atom to give the amino ketone 7 in 71% yield. Cleavage of the tetrahydro-2H-pyran-2-yl(Thp) portion and Jones oxidation of the resulting alcohol 8 gave the amino acid 9 which was cyclized. Final N-debenzylation of 10 provided the natural alkaloid 11 . Only two protective groups were needed in this synthesis. The reaction of N-alkyl-lactams with organometallic reagents is discussed.