Zimmerman studies

The ratio of products 15 and 16 is dependent on the structures, base, and the solvent. The kinetics of the reaction is likewise dependant on the structures and conditions of the reaction. Thus addition or cyclization can be the rate-determining step. In a particularly noteworthy study by Zimmerman and Ahramjian, it was reported that when both diastereomers of 20 were treated individually with potassium r-butoxide only as-epoxy propionate 21 was isolated. It is postulated that the cyclization is the rate-limiting step. Thus, for these substrates, the retro-aldolization/aldolization step reversible. ... 

Most of heat transfer correlations are based on data obtained in flow boiling from relatively large diameter conduits and the predictions from these correlations show considerable variability. Effects of superficial liquid and gas velocity on heat transfer in gas-liquid flow and its connection to flow characteristics were studied by Hetsroni et al. (1998a,b, 2003b), Zimmerman et al. (2006), Kim et al. (1999), and Ghajaret al. (2004). However these investigation were carried out for tubes of D = 25—42 mm. These data, as well as results presented by Bao et al. (2000) in tubes of L> = 1.95 mm and results obtained by Hetsroni et al. (2001), Mosyak and Hetsroni (1999) are discussed in the next sections to clarify how gas and liquid velocities affect heat transfer. Effects of the channel size and inclination are considered. 

Boyd DB, Palkowitz AD, Thrasher KJ, Hanser KL, Whitesitt CA, Reel JK, Simon RL, Pfeifer W, Lifer SL, Takenchi K, Vasudevan V, Kossoy AD, Deeter JB, Steinberg MI, Zimmerman KM, Wiest SA, Marshall WS. Molecnlar modeling and qnantitative strnctnre-activity relationship studies in pnrsnit of highly... 

McDermott DH, Zimmerman PA, Guignard F, Kleeberger CA, Lehman SF, Murphy PM (1998) CCR5 promoter polymorphism and HIV-1 disease progression. Multicenter AIDS Cohort Study (MACS). Lancet 352 866-870... 

The photochemical interconversion of cis- and tra/w-5,6-diphenyl-bicyclo[3.1.0]hexanones has been extensively studied by Zimmerman, Hancock, and Licke.<77) Using isotope dilution analysis, these workers obtained very accurate quantum yields for the various photochemical processes involved in this reaction ... 

Zimmerman and co-workers were also able to obtain some information regarding the multiplicities of the excited states responsible for the initial /9-cleavage through quenching and sensitization studies. It was found that both trans-to-cis and cis-to-trans isomerizations could be sensitized by chlorobenzene under conditions where the latter absorbed over 95% of the light. The same product ratio was obtained under these conditions as in the direct irradiation of the ketones. With 1,3-cyclohexadiene or 2,5-dimethyl-2,4-hexadiene as quenchers nearly 90% of the reaction of the trans isomer could be quenched. Again the ratio of the quenched reaction products was the same as in the unquenched reaction. The reaction of the cis isomer, on the other hand, could not be quenched by 1,3-cyclohexadiene or 2,5-dimethyl-2,4-... 

The photochemistry of l,l,5,5-tetraphenyl-3,3-dimethyl-l,4 pentadiene (1) has been studied in detail by Zimmerman and Mariano.<7) Photolysis of compound (1) gave 1,1-diphenyl-2,2-dimethyl-3-(2,2-diphenylvinyl) cyclopropane ... 

Probably the best example of the manifestation of self-assembly processes in dendritic systems via H-bonds is seen in the recent work of Zimmerman et al. [156]. Dendritic wedges possessing tetraacid moieties (67) self-assembling into a hexameric, disc-like framework (68) was confirmed by SEC and -NMR studies. The tetraacid unit (69) is known to form cyclic as well as linear aggregates in solution via carboxylic acid dimerization (Fig. 30). However, with incorporation of larger dendritic wedges on 69, the hexamer form is preferred. 

A proposed simplified mechanism for the conjugate addition/aldol cyclization, as depicted in Scheme 2.25, is based on detailed mechanistic studies performed on related Rh-catalyzed enone conjugate additions [45]. A model accounting for the observed relative stereochemistry invokes the intermediacy of a (Z)-enolate and a Zimmerman-Traxler-type transition state as shown in 2-110 to give 2-111. 

Zimmerman HE, Goldman TD, Hirzel TK et al (1980) Rod-like organic molecules, energy-transfer studies using sinelo-photon counting. J Org Chem 45 3933-3951... 

H2. Heller, P., Weinstein, H. G., West, M., and Zimmerman, H. J., Enzymes in anemia A study of abnormalities of several enzymes of carbohydrate metabolism in the plasma and erythrocytes in patients with anemia, with preliminary observations of bone marrow enzymes. Ann. Internal Med. 53, 898-913 (1900). 

Zimmerman, J.R. and Brittin, W.E. 1957. Nuclear magnetic resonance studies in multiple phase systems Lifetime of a water molecule in an absorbing phase on silica gel. J. Phys. Chem. 61, 1328-1333. 

From a historical standpoint, the Zimmerman-Traxler study on the stereochemical aspects of the Ivanov reaction is of considerable significance (22). Their investigation revealed that the magnesium enediolate 19a, upon condensation with benzaldehyde (Et2 O, reflux 5 hr), afforded the erythro and threo acids 20E and 20T, respectively, in a 24 76 ratio (eq. [13]). In the analysis of plausible transition states, both chair A and boat B geometries were considered. Zimmerman and Traxler concluded that the major diastereomer 20T could... 

In addition to bimolecular [2-1-2] photocycloaddition reactions similar to the one discussed above [11], absolute asymmetric syntheses employing spontaneously grown chiral crystals have been studied for a number of unimolecular photorearrangement reactions as well. The first report of such an investigation dealt with the photoisomerization of dibenzobarrelene diester 6 to the corresponding dibenzosemibullvalene compound 7 [12], an example of the well-known di-7i-methane (Zimmerman) photorearrangement. Achiral diester 6 crystallizes spontaneously from cyclohexane in the now familiar chiral space... 

Studies of di-ir-methane photochemical rearrangements have been one of the main areas of research in organic photochemistry for many years (for reviews, see Refs. 1-4). The first example of a reaction of this type was reported by Zimmerman in 1967 in the sensitized irradiation of barrelene 1 that yields semibullvalene 2 [5] (Scheme 1). The reaction has been extended to a large number of acyclic and cyclic 1,4-dienes that yield the corresponding vinylcyclo-propanes on irradiation, in the di-ir-methane (DPM) version of the rearrangement. This reaction also takes place when a vinyl unit is replaced by an aryl group. A few representative examples of DPM rearrangements are shown in Scheme 1 [6-9]. 

Direct or triplet-sensitized irradiations have been used in most of the studies on the photoreactivity of 1,4-unsaturated compounds. However, Zimmerman and Hoffacker have reported the novel cyclization of aryl-substituted 1,4-pentadienes... 

A NMR study of water adsorbed on silica gel has been made by Zimmerman el al. 18). Transverse (Ta) and longitudinal (Ti) relaxation times of various amounts of water adsorbed at 25° have been obtained with the use of the spin-echo technique and a two-phase behavior of both Ta and T relaxation times has been observed as illustrated in Figs. 10a and b. Generally only one T value is obtained, as for a single phase, except for x/m g HaO/g solid) values in the vicinity ol x/m = 0.126. Two values of Ta... 

The SC descriptions of the electronic mechanisms of the three six-electron pericyclic gas-phase reactions discussed in this paper (namely, the Diels-Alder reaction between butadiene and ethene [11], the 1,3-dipolar cycloaddition offulminic acid to ethyne [12], and the disrotatory electrocyclic ring-opening of cyclohexadiene) take the theory much beyond the HMO and RHF levels employed in the formulation of the most popular MO-based treatments of pericyclic reactions, including the Woodward-Hoffmarm mles [1,2], Fukui s frontier orbital theory [3] and the Dewar-Zimmerman model [4—6]. The SC wavefunction maintains near-CASSCF quality throughout the range of reaction coordinate studied for each reaction but, in contrast to its CASSCF counterpart, it is very much easier to interpret and to visualize directly. 

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