Some electrical properties of semi-conductor crystals / |nPhyu Phyu Khin. -- 260 St. Catharines, Ont. : [s. n.],

SiC and AtB 12 have been prepared and their resistivities and Hall voltages measured. The resistivities and Hall voltages were measured by the Van der Pauw's method, using spring loaded tungsten contacts. In this method, the major requirement is to have samples of plane parallel surfaces of arbitrary shape with four small contacts at the circumference. Similar measurements were made with a number of SiC crystals obtained from the Norton Research Corporation (Canada)-Ltd., Carolina Aluminum Co., Exolon Co. and Carborundum Co. It was found that resistivity, carrier concentration and mobility of ions depend on the type of impurity. AtB 12 was prepared from the melt containing At and B in the ratio of 4:1. They formed amber-colour pseudo tetragonal crystals. As the crystals obtained were small for electrical measurements, hot pressed lumps have been used to measure their resistivity.

Studies in the synthesis of 4, 5-disubu/stituted phenanthrenes /|nK. Ramakrishnan. -- 260 St. Catharines, Ont. : [s. n.],

The work described in t his thesis was initiated with the intention of exploring new routes for the synthesis of certain 4, 5-disubstituted phenanthrenes. A series of reactions have been investigated in detail and several 4, 5-disubstituted phenanthrenes have been prepared. Some of the methods employed were novel and the yields of products were comparable or even better than the existing routes . A major observation made during the course of this work was the stability of the seven-membered ring system bridging the 4 and 5 positions of the phenanthrene nucleus . It has been found t hat the unbridged structures are not preferred if the compound is capable of isomerising to a bridged form . We have explained this phenomenon in t erms of the stereochemistry of t he 4 and 5 positions of the phenanthrene nucleus as well as the geometry of the bridge . Low temperature NMR studies have been carried out to investigate the conformations of the benzylic hydrogens of some of the 4,5-bridged compounds. However, the results were not conclusive as more than one reason could be attributed t o the observations .

Synthesis and properties of some 4H-1, 3, 4 benzothiadiazines /|nby Darko J. Vukov. -- 260 St. Catharines, Ont. : [s. n.],

The work herein has been divided into five sections. In the first section, a new method of converting N-aroyl- hydrazines to hydrazidic halides is described. The second section deals with the products of reaction of hydrazidic halides with thioacetate ion in acetonitrile at room temperature. A number of new acetylthiohydrazides has been isolated together with corresponding hyclrazidic sulphides. Examination of x-ray data for bis-[~ -(2,6- dibromophenylhydrazono) - benZYl] sulphide revealpd the symmetrical structure as the most probable. In the third section, which consists of the three subsections, the synthesis of the 4H-l,3,4 benzothiadiazine ring system has been extended to 4H-l,3,4 benzothiadiazines with substituents in the 5 and 6-positions. Extension of synthesis also involves 4H-l,3,4 benzothiadiazines with mora than one substituent. Nuclear magnetic resonance spectra of 5 and 6 substituted 4H-l,3,4 benzothiadiazines have been ,. recorded. The section ends with a discussion of the mass spectra of some 4H-l.3,4 benzothiadiazines. In the fourth section, which is divided into two sub- -sections, preparation of 7-nitro substituted 4H-l,3,4 benzothiadiazine from N-thiobenzoyl hydrazine and2,4-dinitro -fluorobenzene is found to be satisfactory. Thiohydrazides react with acetic anhydride, in some cases, to give products identical with acetylthiohydrazides obtained from the hydrazidic halides with thioacetate ion at room temperature. In most of the cases thiohydrazides are found to give anomalous products on reaction with acetic anhydride and mechanisms for their formation are discussed. In the fifth section, which forms three subsections, the 4H-l,3,4 benzothiadiazine ring system with a halogen substituent in the 7-position undergoes electrophilic attack preferentially in 5-posi tion. \fuen the 5-posi tion is occupied by a halogen atom, electrophilic substitution occurs at the 7-position of 4H-l,3,4 benzothiadiazine ring system. Substitution at the 4-nitrogen atom in 4H w l,3,4 benzo- -thiadiazine is extremely slow, probably due to delocalisa- -tion of the nitrogen lone pair in the system. Oxidation of 4H-l,3,4 benzothiadiazines occurs at the sulphur atom under relatively mild conditions. t The Appendix deals with the reaction of N-benzoyl-N - -(2,5-dibromophenyl)hydrazine with p-nitrothiophenol~ The proposed p-nitrothiophenoxy - intermediate may undergo benzothiadiazine formation in a proton exchange system.

The application of gas liquid chromatography to the simultaneous analysis of sugars and sugar phosphates in biological samples /|nby David J. LeBlanc. -- 260 St. Catharines [Ont. : s. n.],

A study was undertaken' to determine the applicability of gas liquid chromatography to the simultaneous analysis of sugars and sugar phosphates from biological samples. A new method of silylation involving dimethylsulfoxide, hexamethyldisilazane, trimethylchlorosilane and cyclohexane (1:0.2:0.1:1) which rapidly silylated sugars and sugar phosphates was developed. Subsequent chromatography on a 5% SE-52 column gave good resolution of the sugar and sugar phosphate samples. Sugar phosphates decomposed during chromatography and were lost at the 7 x 10-3 ~mole level. Acidic ethanol extraction of yeast samples revealed background contamination from the yeast sample, the culture medium and the silylation reagents which would further limit the level of detection obtainable with the glc for sugars in biological samples to the 3 x 10-4 ~mole level.

The crystal and molecular structure of thiamine hydroiodide /|nWilliam Edward Lee. -- 260 St. Catharines [Ont.] : Dept. of Chemistry, Brock University,

The x-ray crystal structure of thiamine hydroiodide,C1ZH18N40S12' has been determined. The unit cell parameters are a = 13.84 ± 0.03, o b = 7.44 ± 0.01, c = 20.24 ± 0.02 A, 8 = 120.52 ± 0.07°, space group P2/c, z = 4. A total of 1445 reflections having ,2 > 2o(F2), 26 < 40° were collected on a Picker four-circle diffractometer with MoKa radiation by the 26 scan technique. The structure was solved by the heavy atom method. The iodine and sulphur atoms were refined anisotropically; only the positional parameters were refined for the hydrogen atoms. Successive least squares cycles yielded an unweighted R factor of 0.054. The site of protonation of the pyrimidine ring is the nitrogen opposite the amino group. The overall structure conforms very closely to the structures of other related thiamine compounds. The bonding surrounding the iodine atoms is distorted tetrahedral. The iodine atoms make several contacts with surrounding atoms most of them at or near the van der Waal's distances A thiaminium tetrachlorocobaltate salt was produced whose molecular and crystal structure was j~dged to be isomorphous to thiaminium tetrachlorocadmate.

The diffusion of Co⠶溩 Zrâ â Tiâ â alloy /|nS. Kumar. -- 260 St Catharines [Ont.] : Dept. of Physics, Brock University,

The diffusion of Co60 in the body centered cubic beta phase of a ZrSOTi SO alloy has been studied at 900°, 1200°, and 1440°C. The results confirm earlier unpublished data obtained by Kidson17 • The temperature dependence of the diffusion coefficient is unusual and suggests that at least two and possibly three mechanisms may be operative Annealing of the specimen in the high B.C.C. region prior to the deposition of the tracer results in a large reduction in the diffusion coefficient. The possible significance of this effect is discussed in terms of rapid transport along dislocation network.

The effect of schooling on student self-concept /|nRonald S. Cowley. -- 260 St. Catharines [Ont. : s. n.],

The following research paper was a study into change in student academic and general self-concept with increase in grade level and age# The majority of literature found by this researcher dealt with self-concept and its relationship to achievement and interactions with others, Review, then, was in these two areas-particularily within the academic setting, but outside of it as well. It wrs hypothesized that there would be a decrease in both academic and general student self-concept with increase in grade level and age. Self-Appraisal inventories, measuring general and academic selfconcept, and Inferential Self-Reports, measuring only academic selfconcept, were the instruments used* Subjects were students, Trade 1 to 13, and ranging in age from 5 to 21„ Although al] Self-Appraisal inventories and all Self-1?eports were very similar, they differed according to three Grade levels: Primary (Grades 1 to 3)> Intermediate (Grades L to 8), and Secondary (Grades 9 to 13) • Students in the Primary division received only their respective Self-Appraisal inventory, while others v/ere administered both inventories designed for their grade level. Scores on the inventories were computed to percents and then mean percents were arrived at for epch grade, each of the three grade levels, each age, and each of three age intervals. In all of these instances Spearman1 s rank order coefficients (!lpff) were calculated and significance, at the *05 level, was determined by referring to a table of critical values for one-tailed tests* Similarily fftff scores were computed, but only for individual grades and ages, and significance was determined at the *0b level* In only one instance, the General Dimension for individual grades, was significance of overall decrease found* Consequently the hypotheses put forth did not gain support* The fltff scores, however, revealed some isolated significant changes for the Academic Dimension, which were generally decreases in mean percents from the last grade of one level to the first grade of the next* For age mean percents, significant changes generally took place at early (5 or 6) and late (20 or 21) ages* A number of reasons for the results were presented and were generally based upon the studentfs encounters, or lack of encounters, with achievement or success* No definite conclusions, relevant to the hypotheses stated^ could be made, although a number of isolated ones were drawn on the basis of significant fltff scores* As well, mention was made of the possible trends or tendencies that were revealed by the results, but that could not, or were not, proven significant by "t's11 or "p's"* Teaching methods stressing improvement in academic, as well as socially related, situations, were recommended and a model teaching approach was presented in Appendix B#

The effects of cultural conditions and parasitism on the lipid composition of choanephora cucubitarum (Berk. Rav.) thaxter /|nJohn M. Deven. -- 260 St. Catharines [Ont. : s. n.],

The fatty acid composition of the total, neutral, sterol, free fatty acid and polar-lipid fractions in the mycelium of Choanephora cucurbitarum was determined. The major fatty acids in all lipid fractions were palmitic, oleic, linoleic and y-linolenic acid. Different lipid fractions did not show any particular preference for any individual fatty acid; however, the degree of unsaturation was different in various lipid fractions. Addition of glutamic acid to the malt-yeast extract medium resulted in the biosynthesis of a number of long-chain fatty acids beyond y-linolenic acid. These fatty acids, e.g. C22~1' C24:0 and C26=Q were never observed to be present in the fungus when grown on a malt-yeast extract medium without glutamic acid. Furthermore, thin-layer chromatographic analysis showed a larger and denser spot of diphosphatidyl glycerol from the mycelium grown on the glutamic acid medium than from the control mycelium. Various cultural conditions such as temperature, age, pH, light and carbon:nitrogen ratio in the growth medium used in this study did not alter the qualitative profile of fatty acids normally present in the organism. Neither did these conditions stimulate the production of further long-chain fatty acids (C20 - C26) beyond y-linolenic acid as observed in growth media containing glutamic acid. These cultural conditions influenced the degree of unsaturation, this being due mainly to changes in the concentration of y-linolenic acid. The fatty acid pattern of the lipid fractions though the same qualitatively, differed quantitatively due to the variation in the y-linolenic acid content under different cultural conditions. The degree of unsaturation of various lipid fractions decreased with increases in temperature, light intensity and pH, but within each treatment the same pattern of decreasing degree of unsaturation with increasing age was observed. The cultural conditions, used in this study, are also known to influence the degree and rate of development of the parasite, Piptocephalis virginiana. A direct correlation was observed between the levels of y-linolenic acid in C. cucurbitarum during the early stages of growth (24 h) and the degree of parasitism of P. virginiana. The amount of y-linolenic acid present in the host mycelium was found to be unrelated to either the dry weight of the mycelium or to the total lipid contents. K. virginiana is confined to host species which produce y-linolenic acid in their mycelium. The lipid profile of the host, C. cucurbitarum, did not show a significant qualitative or quantitative change in the lipid profile as a result of infection by the parasite, P. virginiana,e However, an increase in the total lipid was observed in the infected host mycelium. The significance of these results is discussed.

The electronic spectra and the determination of the excited state geometry of 3A" propynal /|nby Chhiu-Tsu Lin. -- 260 St. Catharines, Ont. : [s. n.],

Impurity free eluission spectra of HCCCHO and DCCCHO have been rephotographed using the electronic-energy-exchange method with benzene as a carrier gas. The near ultraviolet spectra of ReeCHO and DCCCHO were photographed in a sorption under conditions of high resolution with absorption path lengths up to 100 meters. The emission and absorption spectra of Propynal resulting from 3 n 1 t 1\ - A excitation has been reanalyzed in som.e detail. Botrl of the eH out-of-plane wagging modes were found to have negative anharmonicity. A barrier height of 56.8/0.0 cm- 1 and a nonplanar oft , , equilibrium angle of 17 3 /30 are calculated for the V 10/ lJ 11 modes. The in-plane and out-of-plane v1. brational modes in the 3A." and 1a~. ' elec ronic states of Propynal were subjected to a normal coordinate treatment in the approximat :on of tIle Urey-Bradley force field. From the relative oscillator strengths of the trans1·t1·0ns connect i ng t he v ibrat1•0n1ess lA' , state and t,he V1· bron1·C 3· if levels of the A state, the differences in equilibrium configuration were evaluated from an approximate Franck-Condon analysis based on the ground state normal coordinates. As this treatment gave 512 possible geometrical structures for the upper state, it 4 was necessary to resort to a comparison of the observed and calculated moments of inertia along with chemical intuition to isolate the structure. A test of the correctness of the calculated structure change and the vibrational assignment was raade by evaluating the intensities of the inplane and out-oi-plane fundarnental, sequence, and cross sequellce transitions y the exact Franck-Condon method.

The kinetics and mechanism of the thermal decomposition of sec-Butyl peroxide in liquid phase /|nby Sandor Szilagyi. -- 260 St. Catharines, Ont. : [s. n.],

Re~tes artd pJ~oducts of tllerma]. d,ecom.position of sec-butyl peroxide at 110 - 150°C i.n four solvents h,ave been determined. The d,ecompos i tion vJas sb.o\'\Tn to be tlnlmolecl.llar wi tho energies of activation in toluene, benzene, and cyclohexane of 36 .7-+ 1.0, 33.2 +- 1..0, 33.t~) +.. 1.0 I'(:cal/mol respectively. The activation energy of thermal decomposition for the d,et.1terated peroxide was found to be 37.2 4:- 1.0 KC8:1/1TIol in toluene. A.bo1J.t 70 - 80/~ ol~ tJJ.e' pl~od.1..1CtS could, be explained by kn01rJ11 reactions of free allcoxy raclicals J and very littJ...e, i.f allY, disPl"Opox~tiol'lation of tll10 sec-butoxy radica.ls in t116 solvent cage could be detected. The oth,er 20 - 30% of the peroxide yielded H2 and metb.:'ll etb..yl 1{etol1e. Tl1.e yield. o:f H2 "'lIas unafJ:'ected by the nature or the viscosity of the solvent, but H2 was not formed when s-t1U202 lrJaS phctolyzed. in tolttene at 35°C nor 'tl!Jrl.en the peroxide 1;'JaS tl1.ermally o..ecoJnposed. in the gas p11ase. ~pC-Dideutero-~-butYlperoxide was prepared and decomposed in toluene at 110 - 150°C. The yield of D2 was about ·•e1ne same 248 the yield. of I{2 from s-Bu202, bU.t th.e rate of decomposition (at 135°C) 1iJas only 1/1.55 as fast. Ivlecl1.anisms fOl') J:1ydrogen produ.ction are discussed, but none satisfactorily explains all the evidence.

The kinetics and mechanism of the thermal decomposition of bis diphenyl methyl and related peroxides in liquid phase /|nby C. Thankachan. -- 260 St. Catharines, Ont. : [s. n.],

Rates and products have been determined for the thermal decomposition of bis diphenyl methyl peroxide and diphenyl methyl tert* butyl peroxide at 110@~145@C* The decomposition was uniformly unimolecular with activation energies for the bis diphenyl methyl peroxide in tetrachloroethylene* toluene and nitrobenzene 26,6* 28*3f and 27 Kcals/mole respectively. Diphenyl methyl tert* butyl peroxide showed an activation energy of 38*6 Kcals/mole* About 80-90% of the products in the case of diphenyl methyl peroxide could be explained by the concerted process, this coupled with the negative entropies of activation obtained is a conclusive evidence for the reaction adopting a major concerted path* All the products in the case of diphenyl methyl peroxide could be explained by known reactions of alkoxy radicals* About 80-85% of tert butanol and benzophenone formed suggested far greater cage disproportionation than diffusing apart* Rates of bis triphenyl methyl peroxide have been determined in tetrachloroethylene at 100-120@C* The activation energy was found to be 31 Kcals/mole*

The pancreatic islet system of the rock bass /|nby Edward Francis Squires. -- 260 St. Catharines, Ont. : [s. n.],

The endocrine pancreas of the rock bass (Ambloplites rupestris) was examined by light and electron microscopy. Two cell types with staining properties similar to mammalian A and B cells, and a third, non-staining cell type were found in the spherical pancreatic islets that were surrounded by a connective tissue capsule and embedded in two small masses of exocrine tissue. From an analysis of the ultrastructure of the A and B cells, a secretory cycle for each of these cell types was proposed. The secretory cycle of the A cell consisted of three well defined stages: (1) A cell production stage: during which A granule formation occurred in the sacs of the Golgi apparatus and the cell was characterized by the presence of numerous secretory granules, some elements of lamellar endoplasmic reticulum, and a homogeneously granular nucleus. The cytoplasm contained few distended cisternae, variable numbers of free ribosomes, microtubules and small vesicles. (2) A cell release stage: during which the release of A granules occurred and the cell usually contained several large distended cisternae and variable numbers of secretory granules. Granule release mechanisms included exocytosis, by which individual granules were released into the extracellular space after their membranes fused with the plasmalemma, and emiocytosis, by which one or more granules were released into a large cisterna whose membrane fused with the plasmalemma and formed a pore through which the cisternal contents passed out of the cell. (3) A cell reorganization stage: during which the changeover from the release stage to the production stage occurred and the reorganization of organelles and membrane structures took place. The cell contained few secretory granules and numerous small endoplasmic reticular cisternae. The cytoplasm exhibited less electron density than either of the other two stages. The A granule after formation underwent a series of morphological changes which were described in four numerically identified phases. The secretory cycle of the B cell consisred of two stages: (1) B cell production stage: during which the B granule formation occurred in the sacs of the Go1gi apparatus. The cell was characterized by an irregular outline, the presence of numerous secretory granules, and an irregularly shaped nucleus which contained variable amounts of clumped chromatin. The cytoplasm contained moderate amounts of lamellar endoplasmic reticulum studded with ribosomes, several small vesicles, and an active Go1gi apparatus. (2) B cell release stage: during which the release of B granules occurred. The cell contained a rounded nucleus with dispersed chromatin, several distended endoplasmic reticular cisternae and a variable number of secretory granules. Granule release occu~ by emiocytosis and exocytosis similar to that found for the A cell.

The preparation and reactions of some 1, 2-dipolar species /|nI. D. Brindle. -- 260 St. Catharines, Ont. : [s. n.],

This research was directed mainly towards the investigation of the reactions of allylic amineimides. The work can be divided into two main sections. Section 1 of the thesis deals mainly with thermolysis studies of amineimides. Sections 1a and 1b represent a comprehensive survey of amineimide literature up to 1971. N-A1ly1-N,N-dirnethylarnine-benzirnide was prepared and rearranged at 1400 to l-allyl-1-benzoyl-2,2-dimethylhydrazine. A tentative mechanism involving an initial migration to the carbonyl oxygen was disproved by incorporating the amineimide system into a five-membered ring. N,N~Dimethyl-N-propargylamine-benzimidedid not rearrange on heating; but the hydrobromide, on heating, disproportionated to give 1-benzoyl~2,2,2-trimethylhydraziniumbromide and I-benzoyl-2,2~ dimethylhydrazine. l-Ally'l--l, I-dimethyl-2-benzoy-lhydrazinium bromide and 1~benzoy-1-2,2, 2-trimethy-lhydrazinium iodide both disproportionated to give l~benzoyl-2,2-dimethylhydrazine. Section 1 concludes with a discussion of the mechanisms of ally'lic migrations in amineimides proposed by J. E. Baldwin. Section 2 deals with the formation of five-membered heterocyclic compounds from amineimides by bromination. 1,1-Dimethyl-2benzoyl- 4-bromopyrazolidinium bromide was formed from N-allyl-N,Ndime thy-lamtne-benzimide , 1,1-dimethyl-2-benzoyl-4-bromopyrazol-3enium bromide from N,N~dimethyl-N-propargylamine~benzimidevia the unusual acetylenic "bromonium" ion. Hydrogenolysis of both heterocyclic compounds gave the same product. The preparation was extended by forming 2,2-dimethyl-4-bromoisoxazolinium bromide from N-allylN, N-dimethylamine-N-oxide. Sections 3 and 4 cover a number of unsuccessful attempts to synthesise other amineimides and l,2-dipolar species.

The problem of national integration in plural societies : a case study of Pakistan, 1947-71 /|nMuhammed A. Quddus. -- 260 St. Catharines [Ont. : s. n.],

Pakistan had a plural society per excellence. Its people were divided geographically between two separate regions, spoke different languages, had different cultures and economic structures. Like other plural societies elsewhere, Pakistan also faced the problem of national integration. Cleavages along the lines of traditional attachments are fundamental to any plural society, as they were in Pakistan. But their political manifestation could have been kept within managable limits if the Central Government, overwhelmingly composed of the West Pakistanis, was seriously committed to the task. All that Pakistan needed to maintain her integrated existence was deliberate, calculated and conscious efforts on the part of the Central Government to give the Bengalis, the majority linguistic and geographic group in the country, a partnership in the state of Pakistan, an effective power in the decision-making process of the country, a reasonable share from the economic resources of the country, and to show respect to their hopes and aspirations. In addition, Pakistan needed a national platform to bring her divergent linguistic and geographic groups toge~her for some common, national purpos~s. Political parties were the only institutions which could have served this purpose. Pakistan miserably failed to sustain national political parties and failed to satisfy Bengalis' demands. This failure eventually resulted in the falling apart of the political system of Pakistan in 1971.

The Smiles rearrangement in hydrazidic systems and related syntheses /|nG. A. Pawelchak. -- 260 St. Catharines, Ont. : [s. n.],

This research was directed towards the investigation of the Smiles rearrangement in hydrazidic systems and the synthesis of related heterocyclic compounds. The work can be conveniently divided into two main sections. Section 1 of the thesis relates to the synthesis and examination of the O+N migration of phenoxy- derivatives of hydrazidic halides. In general, hydrazidic halides were found to react with 2-nitrophenol and 4-nitrophenol to give corresponding a-nitrophenoxy- compounds. These a-nitrophenoxy- compounds were found to rearrange in warm base to give the corresponding N-benzoyl compounds via a proposed five-membered transition state. Experiments conducted in styrene revealed no radical contribution to the rearrangement. Cross-over product analysis indicated the rearrangement as intramolecular and consistent with the Smiles rearrangement. The preparation of N-a-chlorobenzylidene-N'-2-nitrophenyl- -N'-(2,4-dibromophenyl)hydrazine from N-benzoyl-N'-2-nitrophenyl- N'-(2,4-dibromophenyl)hydrazine was accomplished using phosphorus oxychloride. Examination of this hydrazidic chloride indicated a marked decrease .in reactivity as compared to the N-a-chlorobenzylidene-N'-phenylhydrazine case. Section 2 concerns itself with the preparation of heterocyclic compounds using an analogy of the five-membered transition state present in the Smiles rearrangement of a substituted benzylidene derivatives A new preparation of 2,4-phenyl1,3,4- oxadiazol-S-one using N-benzoyl-N'-phenylhydrazine and ethyl thiochloroformate is reported. Two new preparations of N-a-thiobenzoyl-N'-(2,4-dibromophenylhydrazine are reported using sodium hydrosulfide in conjunction with N-a-bromobenzylidene-N'-(2,4-dibromophenyl)hydrazine in the first, and phosphorus pentasulfide with N-benzoylN'-( 2,4-dibromophenyl)hydrazine in the second. The latter is preferred due to the formation of a sulfide co-product in the former. Two preparations of 2-phenyl-4-(2,4-dibromophenyl)-1,3,4- thiadiazol-S-one are reported using N-thiobenzoyl-N'-(2,4-dibromophenyl) hydrazine and ethyl chloroformate and ethyl thiochloroformate Two rapid and easy preparations of 2-phenyl-4-(2,4-dibromophenyl)- 1,3,4-triazol-S-one are reported using ethyl chloroformate and ethyl thiochloroformate. Sodium cyanate in conjunction with a-aminobenzylidene-N'-(2,4-dibromophenyl)hydrazine also provided 2-phenyl-4-(2,4-dibromophenyl)-1,3,4-triazol-S-one Section 2 concludes with an examination of two possible mechanistic routes to the prepared heterocycles.