Diels-Alder Reactions Experiment

Diels-Alder Reactions Experiment Abstract A Diels Alder reaction was done during this experiment between anthracene and maleic anhydride via to yield 9, 10-dihydroanthracene-9, 10-ÃŽÂ ±, ÃŽÂ ²-succinic anhydride. Anthracene was the diene and maleic anhydride was the dienophile. Following recrystallization of the product using xylene and vacuum filtration, a percent yield of 39.9% was calculated for the recrystallized product that was collected. The yield may have been low due to several of the crystals being stuck to flask and not going into the funnel, and there may have been other sources of error. The percent recovery from recrystallization was 56%. The melting point of the recrystallized product was 260 264 °C, while the literature melting point of 262 264 °C. Comparing these values shows that the product was indeed and that recrystallization yielded a purer product. Upon examination of an infrared spectrum of the product and of anthracene and maleic anhydride spectra, the data showed that the product spectru m had similarities with both spectrums for anthracene and the maleic anhydride. This indicated that 9, 10-dihydroanthracene-9, 10-ÃŽÂ ±, ÃŽÂ ²-succinic anhydride was a product of both anthracene and maleic anhydride, and thus that the experiment was successful. Figure 1: Reaction scheme of 9,10 dihydroanthracene-9, 10- ÃŽÂ ±, ß-succinic anhydride Introduction The 1950, Otto Paul Hermann Diels and Kurt Alder were awarded Nobel Prize in chemistry for their work on the discovery and development of [4+2] cycloaddition reactions. Diels-Alder reactions are used to synthesize new carbon-carbon bonds, more commonly they form six-membered cyclic compounds. The Diels-Alder reaction is categorized as a pericyclic reaction, which involves the overlap of spatial orbitals as well as the hybridization and delocalization of the molecules.1 The Diels-Alder reaction is a member of a class of reactions called cycloadditions, which are under pericyclic reactions. Usually, the reaction involves three à Ã¢â€š ¬ bonds, two from the diene and one from the dienophile in the reaction to form a six-membered ring.Since this reaction involves four à Ã¢â€š ¬ electrons in the diene and two à Ã¢â€š ¬ electrons from the dienophile, it is sometimes referred to as a 4à Ã¢â€š ¬ + 2à Ã¢â€š ¬ cycloaddition. Various chiral auxiliaries and catalysts for asymmetric Die ls-Alder chemistry have been developed that allow the cycloaddition to proceed with very high levels of selectivity.3 The use of chiral Lewis acid catalysts and high pressure to enhance the selectivity and rate of these [4à Ã¢â€š ¬ + 2à Ã¢â€š ¬]-cycloadditions have further extended the scope of this remarkable reaction.1,2 Diels-Alder reactions are normally favored by electron donating groups on the diene and electron withdrawing groups on the dienophile. The diene must be able to achieve a s-cis conformation to generate the cis double bond in the cyclohexene product.3 Acyclic dienes may rotate around a single bond, but dienes locked in the s-trans conformation do not react.3 The purpose of this experiment is to yield 9,10-dihydroanthracene-9,10-ÃŽÂ ±, ÃŽÂ ²-succinic anhydride via a Diels Alder reaction between anthracene and maleic anhydride, as shown in figure 1. Anthracene acts as the diene and maleic anhydride functions as the dienophile. Xylene is used as a high boili ng temperature solvent so that the reaction will proceed quickly. A key characteristic of these reactions is their stereospecificity.3 Based on the interaction between a cyclic diene and a dienophile, different stereoisomeric compounds are formed. Stereochemistry represents a major component of the Diels-Alder reaction.2 Due to the interaction and arrangement between the conjugated diene and dienophile, an endo and exo product could be formed, which can characterize the reaction as stereo- and/or regioselective. Experimental Instruments used: The instruments that were used were the Thomas Hoover Melting, and a Nicolet IR 100 FT-IR were used in this experiment. Procedure and Observations: A reflux apparatus was assembled. Xylene (6 mL), anthracene (0.5 g), and maleic anhydride (0.25 g) were added to a round bottom flask (25 mL). The solution turned a yellow color when the reactants were added together. The reflux was then started, and once it began to boil, it was boiled for 30 minutes. A watch glass was weighed (35.55 g), which the product would later be transferred to. After reflux, the solution was cooled to room temperature, and then xylene (6 mL) was added to a test tube and laced into an ice bath. The solution appeared to be a golden yellow color after the reflux. Next, xylene (15 mL) was added to a beaker (50 mL), and then a vacuum apparatus was assembled. The solution was placed chilled for 5 minutes, and it became cloudy and crystals began to form. The solution was filtered through a Buchner funnel on the vacuum filtration. After the vacuum filtration, the crude product were light yellowish-brown crystals. Xylene (15 mL) was boiled , and was then added to the crude product, just enough to cover it, and was heated. The crystals began to dissolve the hot xylene was added, and as it dissolved the color became lighter and clearer. Once dissolved, the solution was then placed into an ice bath, after being cooled to room temperature. It was then put through the vacuum filtration; the recrystallized product was allowed to dry, and then weighed (0.28 g). Finally, the product was analyzed using IR and the melting point apparatus. References C. Oliver Kappe, S. Shaun Murphree, Albert Padwa, Synthetic applications of furan Diels-Alder chemistry, Tetrahedron, Volume 53, Issue 42, 1997, Pages 14179-14233, ISSN 0040-4020. Wade, L.G., Jr. The Diels-Alder Reaction of Anthracene and Maleic Anhydride (1998). Simek, Jan William., and L. G. Wade. Solutions Manual Organic Chemistry, Eighth Edition L.G. Wade, Jr. Boston: Pearson, Boston, 2013. Print.

J.J. Thomson †Discovery of the Electron

CHE003 Chemistry Individual Assignment J. J. Thomson – Discovery of the electron Table of Contents Introduction2 Biographical information3 Background information4 Experimental information5 Impact6 Conclusion7 J. J. Thomson – Discovery of the electron Introduction The discovery of the electron is affirmative and justly credited to the English physicist Sir Joseph John Thomson (Weinberg, 2003). He had found and identified the electron in Cavendish Laboratory, Cambridge in 1897. From many experiments, Thomson had certified that cathode rays carry negative charge and identified the cathode rays inside vacuum tubes as being electric currents composed of these tiny electrons (Hamblin, 2005). It was the crucial first step in the development of the twentieth-century concept of the atom (Simmons, 1996). In the following paragraphs, I will introduce the Thomson’s life and his important achievements. Biographical information J. J. Thomson was born at Cheetham Hill, a suburb of Manchester, England on December 18, 1856. His father Joseph Thomson was a publisher and book dealer; his mother was Emma Swindles, a housewife. The family’s environment was not good for learned, but he was excellent in study and had an exceptional memory. When Thomson was fourteen in 1870, he enrolled in Owens College and had been taught by the physics professor, Balfour Stewart. Then he entered Trinity College in 1876, as a minor scholar. In 1880, Thomson became a Fellow of Trinity College, when he was Second Wrangler and Second Smith's Prizeman; he remained at Cambridge for the rest of his life, and becoming lecturer in 1883. In 1884, Thomson was named Cavendish Professor of Experimental Physics at an exceptionally young age (Simmons, 1996). On April 30, 1897, was his first time announced preliminary discovery of electron during lecture in Royal Institute, England. In 1903, Thomson published a summary of his work; Conduction of electricity through gases, and he created the â€Å"plum-pudding† model, which is the first model of atom. Thomson won the Nobel Prize for Physics in 1906, a knighthood in 1908, and the Presidency of the Royal Society in 1915. He was also a member of the Board of Investigation and Research, which served Britain in World War One (Weinberg, 2003). After that, he resigned from the Cavendish Laboratory in 1919 to become Master of Trinity College, until died on August 30, 1940 (Hamblin, 2005). In addition, he married with Rose Elisabeth in 1980, they had one son; George Paget Thomson; also won the Nobel Prize for Physics in 1937, and one daughter. Background information In the end of nineteenth century and the beginning of the twentieth century were exciting and revolutionary time for physics (Franklin, 2004). They began to investigate the behavior of electricity in evacuated tubs. The conduction of electricity through a near vacuum appeared to produce a kind of â€Å"ray†, lighting up the inside of the tube. The cathode rays appeared to be like light, and thus some physicists concluded that they were wave but other evidence proofed that the rays were in fact material in nature. During 1894 to 1897, Thomson was investigated the phenomenon of cathode ray, which had been discovered in 1858 (Ne’eman& Kirsh, 1997). In 1897, he made a significant discovery that the â€Å"rays† were indeed built up of particles and that they were the constituents of all atom. Thomson believed that his experimental evidence, by electromagnetic deflection and measuring the kinetic energy of the ray, had proven it. In the first, he did not initially call it electron, but chose the word â€Å"corpuscle† to emphasize the material nature of the particle. Thomson had found the new particle was very much matter, and he believed that it was the fundamental form of matter in atoms (Hamblin, 2005). Moreover, Albert Einstein introduced his special theory of relativity, which fundamentally changed our concepts of space and time in 1905. Follow by this discovered, people also had changed the way to think about nature and formed an integral and important part of the physics of the time (Franklin, 2004). Experimental information The purpose of Thomson’s experiments in 1897 was to investigate the nature of the then recently discovered cathode rays. He was tried to decide between the view that rays were negatively charged, material particles and the view that they were disturbances in the â€Å"Aether†, the medium through which physicists believed that light waves traveled at the time (Franklin, 2004). In the first of several experiments, Thomson wanted to proof that the cathode rays carried negative charge. He placed two metal plates, connected to a battery, inside a cathode tube, creating a magnetic filed through which the rays would have to pass (Simmons, 1996). The rays were emitted from the negative electrode â€Å"the cathode† and caused a glow when they impinged on the glass or a plate coated with Zinc Sulphide fixed inside the tube. There is another physicist, William Crookes, has been published that the cathode rays were a stream of particles carrying negative charges substances in 1897 (Ne’eman& Kirsh, 1997). Thomson certified this by showing that the rays could be deflected from their straight path by a magnetic or an electric field, and that their behavior under the influence of these fields was exactly what would be expected of a stream of negatively charged particles. By measuring the deflection of the rays in combined electric and magnetic fields of different strengths he was able to calculate the speed of the particles and the ratio between the charges carried by each particle (e) and its mass (m), but no way could be found to calculating the charge and the mass separately. The ratio e/m of the particle was found to be independent of the type of metal of which the cathode was made or residual gas in the tube. Thomson repeated these experiments and found that the particles, which the light knocked out of the metal surface, were identical to the particles constituting the cathode rays. Thus he got the conclusion that these particles were present in all matter, and that by means of an electric voltage or irradiation with light they could be extracted from certain substances (Ne’eman& Kirsh, 1997). The particles were given the name â€Å"electrons† (corpuscle). Impact Firstly, the electron was not only the first of the basic particles to be clearly identified but also by far the lightest of the elementary particles (Weinberg, 2003). Secondly, as a consequence of its lightness, charge and stability, the electron has a unique importance to physics, biology and chemistry. The heat of our sun is produce by the electrons participate in the nuclear reaction. In addition, every atom in the universe consists of a dense core, was surrounded by a cloud of electrons. For chemistry, the chemical differences between one element and another one, depend almost entirely on the number of electrons in the atom, and the chemical forces that hold atoms together in all substances are due to the attraction of the electrons in each atom for the nuclei of the other atoms (Weinberg, 2003). Lastly, the cathode ray tube that we used in television screen and computer monitor today, was developed from experimental apparatus. It is basic from a glass tube plugged by metal electrodes, with the air evacuated and some specific gas pumped in. When the electrodes are connected to a battery with enough voltage, the cathode rays strike the opposite end of the tube and glow or fluoresce. The rays are streams of electrons, not light rays (Simmons, 1996). Conclusion In conclusion, Thomson had constituted one of the important milestones in physics: Cathode rays consist of particles that are elementary and found in all matter. Because of his famous experiments, the Cavendish Laboratory was already became a paradise for physicists at that moment, and number of his students also won the Nobel Prize. With change through time, there are nearly sixteen types of elementary particles have been known so far, but only one particle type has always remained on the list: the electron (Weinberg, 2003). Therefore, the achievements of J. J. Thomson were still having influence in the world. Bibliography List Dahl, P. F. (1997). Flash of the cathode rays: A history of J J Thomson's electron. USA: Institute of Physics Publishing. Franklin, A. (2004). Are there really neutrinos? : An evidential history. USA: Westview Press. (pp. 17-21). Hamblin, J. D. (2005). Science in the early twentieth century: An encyclopedia. Santa Barbara, CA, USA: ABC-CLIO, Inc. (pp. 18-20, 96-98, 320-321). Hollow, R. & Morgan, A. (1990). History of ideas in physics: Gravitation and atomic structure. Australia: Brooks Waterloo. (pp. 54-56). Ne'eman, Y. & Kirsh, Y. (1996). The particle hunters (2nd ed. ). Cambridge: Cambridge University Press. (pp. 2-5). Simmons, J. (1996). The scientific 100: A ranking of the most influential scientist, past and present. USA: Carol Publishing Group. (pp. 152-155). Weinberg, S. (2003). The discovery of subatomic particles. Cambridge: Cambridge University Press. (pp. 9-11).

The Secret Truth About Essay Critique Samples Uncovered

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To Kill A Mockingbird Chapter Questions - 2540 Words

To Kill A Mocking Bird – Chapter Questions 1) What do we learn about Atticus Finch, his children and the town of Maycomb in the first chapter? a) Atticus Finch is a wise, single father. He is a qualified, intelligent and distinguished lawyer practising in the south of Alabama in a rural town named Maycomb. Atticus has a high moral integrity and is bred from an upper-class background. He has a brother named Jack Finch and a sister named Alexandra. Atticus has two children named Jean-Louise Finch and Jem Finch. Jem is a quiet, studious boy who loves reading and football. Scout (Jean) is a tomboyish, confident girl who loves rolling in mud in her overalls and reading any book she can get her hands on. Maycomb is a close knit, old and†¦show more content†¦On the Sunday evening Atticus travels to the jail to stand guard and protect Tom Robinson as he was notified of possible â€Å"trouble and disturbance at the Jail’. When Jem and Dill run into the crowd, led by Scout, they are suddenly aware that they have walked into a bad situation. Though Jem realises the situation is precarious, he made a decision to stay a nd help Atticus protect Tom even after his father’s thorough protests. Dill and Scout on the other hand, are still too young to completely understand what is going on. They stand and fight with Jem though, knowing what he is doing will be what is right. Atticus continues to plea, order, threaten and at times, almost beg in a desperate attempt for the children to go home. He realises what a dangerous situation this is and could become if the mob turns violent so wants to protect them from this. 10) Why did the ‘Lynch Mob’ go home? What main point do you think the novelist hoped to make by introducing this episode into the story? a) The Lynch mob left the jail on Mr Cunningham’s command. Scout, who misunderstanding what’s going on, reminded him of his own human dignity. 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