The synthesis and fluxional behavior of the first [2.1.2.1] metacyclophane

8,15,23,30-Tetramethyl[2.1.2.1]metacyclophane,4, is synthesised. Variable temperature ¹Hmr and ¹³Cmr spectra indicate that 4e is the most likely conformation and that at temperatures above 50°C the molecule is fluxional (ΔG^≠₃₂₃ = 15.4 kcal/mole).     

Structure and synthesis of physoperuvine: x-ray crystal and molecular structures of the n-benzoyl derivatives of (±)-3- and (+)-4-methylaminocycloheptanone

Single-crystal X-ray analyses have defined the structures and solid-state conformations of (±)-N-benzoyl-3-methylaminocycloheptanone [(±)-$\text{3}$]and (+)-N-benzoyl-4-methylaminocycloheptanone [(±)$\text{4}$]. Resolution of (±)-[4- methylaminocycloheptanone α 1-hydroxytropane]to yield the (+)-enantiomer. Identical in all respects with the free base from natural (+)-physoperuvine, was achieved via the di-p-toluoyl-(+)-tartrate salt.     

Mechanistic Aspects of Carbon Nanotube Nucleation and Growth

The discovery, synthesis, characterization, and applicability of carbon nanotubes have produced tremendous excitement and interest among scientists and engineers. In particular, the use of these unique tubular nanostructures for new strong lightweight materials, nanoelectronics, fuel storage and cells, electron emitters and bio, scanning probe microscopy, and chemical sensing devices has created an intense effort to advance the synthesis so as to mass produce carbon nanotubes with control over diameter and helicity. The massive and controlled synthesis of this heralded nanostructure has been a great challenge. Although significant progress has advanced the preparation, more synthetic development is required. The syntheses have so far involved three main approaches: arc discharge vaporization, laser vaporization, and catalytic chemical vapor deposition. The synthetic trend has progressed to a point where further advancement with these techniques will require a better understanding of the mechanism of nucleation and growth. The mechanics of carbon nanotube nucleation and growth involve very complex and diverse phenomena occurring under extreme conditions and on the mesoscopic scale. As yet the detail mechanism is unknown. Difficulties with experimental probing and computational simulation have increased the mystery of this mechanism. This review presents an account of research on the synthesis of carbon nanotubes and the mechanism of formation. This overview includes all three mentioned synthetic approaches and hybrids thereof. On the basis of this broad account a comprehensive mechanism for carbon nanotube nucleation and growth naturally arises. This mechanism is qualitative and it hopes to inspire more quantitative exploration and synthetic advancement.     

Dimethyldihydropyrene-dehydrobenzoannulene hybrids: studies in aromaticity and photoisomerization

The synthesis and study of dehydrobenzoannulene (DBA)-dimethyldihydropyrene (DDP) hybrids as models for the investigation of aromaticity in weakly diatropic systems is reported. Three new monofused DBA-DDP hybrids have been synthesized, and their NMR spectra are discussed with regard to quantifying the aromaticity remaining in multibenzene-fused DBAs. Nucleus-independent chemical shifts, determined at a series of locations for each compound, bond lengths, and (1)H and (13)C NMR chemical shifts were calculated and used to probe the aromaticity of these hybrids. Systems where more than one annulene/DBA is fused to the DDP core have also been obtained, and their potential use in photoinduced isomerization applications is discussed.     

Mechanistic insights into the photochromism of trans-10b,10c-dimethyl-10b,10c-dihydropyrene derivatives

A series of dimethyldihydropyrene derivatives was studied to elucidate the photochemical mechanism associated with the switching between the dimethyldihydropyrene (DHP, closed) and metacyclophanediene (CPD, open) forms of the molecule. Quantum yields of ring opening and closure, fluorescence quantum yields and lifetimes, as well as laser flash photolysis studies were performed to establish the effect of substituents on the switching efficiency. Ring opening of the DHPs occurs from the first singlet excited state. The low quantum yields for the ring opening reaction observed (< or =0.042) are a consequence of the low rate constant (< or =1.7 x 10(7) s(-1)) for this process. The quantum yields for ring closure of the CPD were determined for select compounds and were of the order of 0.1-0.4. These results show that the efficiency for ring opening of this class of compounds is intrinsically low, but can be modulated to some extent by the introduction of substituents. These properties should be taken into account when considering what type of photoswitching devices DHPs might be useful for.     

Identification of omega hydroxy fatty acids in biological samples as their pentafluoropropyl derivatives by gas chromatography/mass spectrometry with positive and negative ion detection

A simple one-step procedure for derivatization of the omega hydroxy fatty acids 20-hydroxyeicotetraeonic acid and 12-hydroxylauric acid is presented. The procedure involves acylation of the terminal hydroxy group and esterification of the carboxylic acid with a mixture of pentafluoropropionic anhydride and pentafluoropropanol. Positive and negative ion spectra for the derivatives are presented. The procedure was used to demonstrate conversion of arachidonic acid to 20-hydroxyeicosatetraeonic acid and lauric acid to 12-hydroxylauric acid in kidney microsomal incubations. The reaction appears to be specific, since derivatives of subterminal fatty acids (secondary alcohols) could not be detected.     

The mass spectra of substituted 2-methylbenzophenones

The mass spectra of some methoxy and methyl derivatives of 2-methylbenzophenone have been examined. Loss of a substituents from 3′-and 4′-positions as well as the previously known loss from 2′-positions are important fragmentation processes. Thus, these fragmentations are of little use in locating substituents on benzophenones of unknown structure. Deuterium labelling shows the [M - 1]⁺ ion from 3′,4,4′,5,5′-pentamethoxy-2-methyl benzophenone to be due largely to loss of hydrogen from 2′- and 6′-positions.