Borane, any of a homologous series of inorganic compounds of boron and hydrogen or their derivatives.
The boron hydrides were first systematically synthesized and characterized during the period 1912 to roughly 1937 by the German chemist Alfred Stock. He called them boranes in analogy to the alkanes (saturated hydrocarbons), the hydrides of carbon (C), which is the neighbour of boron in the periodic table. Because the lighter boranes were volatile, sensitive to air and moisture, and toxic, Stock developed high-vacuum methods and apparatus for studying them. American work on boranes began in 1931, carried out by Hermann I. Schlesinger and Anton B. Burg. Boranes remained primarily of academic interest until World War II, when the U.S. government supported research to find volatile uranium compounds (borohydrides) for isotope separation, and the 1950s, when it supported programs to develop high-energy fuels for rockets and jet aircraft. (Boranes and their derivatives have much higher heats of combustion than hydrocarbon fuels.) William Nunn Lipscomb, Jr., received the 1976 Nobel Prize for Chemistry “for his studies on the structure of boranes illuminating problems of chemical bonding,” while one of Schlesinger’s students, Herbert Charles Brown, shared the 1979 prize for his hydroboration reaction (1956), the remarkably easy addition of BH3 (in the form of BH3 · S) to unsaturated organic compounds (i.e., alkenes and alkynes) in ether solvents (S) at room temperature to yield organoboranes quantitatively (that is, in a reaction that proceeds wholly, or almost wholly, to completion). The hydroboration reaction in turn opened up new avenues of research in the area of stereospecific organic synthesis.
The boranes that were prepared by Stock had the general composition BnHn + 4 and BnHn + 6, but more complex species, both neutral and negative (anionic), are known. The hydrides of boron are more numerous than those of any other element except carbon. The simplest isolable borane is B2H6, diborane(6). (The Arabic numeral in parentheses indicates the number of hydrogen atoms.) It is one of the most extensively studied and most synthetically useful chemical intermediates. It is commercially available, and for years many boranes and their derivatives were prepared from it, either directly or indirectly. Free BH3 (and B3H7) are very unstable, but they can be isolated as stable adducts (addition products) with Lewis bases (electron-donor molecules)—e.g., BH3 · N(CH3)3. Boranes may be solids, liquids, or gases; in general, their melting and boiling points increase with increasing complexity and molecular weight.
|Physical properties of some common boranes|
Structure and bonding of boranes
Rather than exhibiting the simple chain and ring configurations of carbon compounds, the boron atoms in the more complex boranes are located at the corners of polyhedrons, which can be considered either as deltahedrons (polyhedrons with triangular faces) or deltahedral fragments. Developing an understanding of these boron clusters has done much to help chemists rationalize the chemistry of other inorganic, organometallic, and transition-metal cluster compounds.
One of several systems of nomenclature suggested by the International Union of Pure and Applied Chemistry (IUPAC) employs characteristic structural prefixes: (1) closo- (a corruption of “clovo,” from Latin clovis, meaning “cage”), deltahedrons of n boron atoms; (2) nido- (from Latin nidus, meaning “nest”), nonclosed structures in which the Bn cluster occupies n corners of an (n + 1)-cornered polyhedron—i.e., a closo-polyhedron with one missing vertex; (3) arachno- (Greek, meaning “spider’s web”), clusters that are even more open, with boron atoms occupying ncontiguous corners of an (n + 2)-cornered polyhedron—i.e., a closo-polyhedron with two missing vertices; (4) hypho- (Greek, meaning “to weave” or “a net”), the most open clusters, with boron atoms occupying n corners of an (n + 3)-cornered closo-polyhedron; and (5) klado- (Greek, meaning “branch”), n vertices of an n + 4-vertex closo-polyhedron occupied by n boron atoms. Members of the hypho- and klado- series are currently known only as borane derivatives. Linkage between two or more of these polyhedral borane clusters is indicated by the prefix conjuncto- (Latin, meaning “join together”). For example, conjuncto-B10H16 is produced by joining the B3H8 units from two B6H9 molecules via a B−B bond.
One of the reasons for the great interest in boranes is the fact that they possess structures different from any other class of compounds. Because the bonding in boranes involves multicentre bonding, in which three or more atoms share a pair of bonding electrons, boranes are commonly called electron-deficient substances. Diborane(6) has the following structure:
This structure involves three-centre bridge bonding, in which one electron pair is shared between three (rather than two) atoms—two boron atoms and one hydrogen atom. (Seechemical bonding: Advanced aspects of chemical bonding: Boranes for a discussion of the three-centre bond.) The ability of boron to form such bonds in addition to normal covalent bonds leads to the formation of complex polyhedral boranes.
Reactions and synthesis of boranes
Although the simplest boranes—e.g., B2H6—are spontaneously flammable in air (burning with a characteristic green flame) and very reactive toward solvents containing replaceable protons, reactivity generally decreases with increasing molecular weight. Some of the higher-molecular-weight polyhedral anions, such as B10H102− and B12H122−, are remarkably stable in air, water, and heat. Arachno-boranes are generally more reactive and less thermally stable than nido-boranes, which in turn are more reactive and less thermally stable than closo-boranes. Alfred Stock first obtained mixtures of boranes in low yield by treating magnesium boride (Mg3B2) with hydrochloric acid (HCl). Diborane is more easily prepared in high yield by reaction of iodine (I2) with sodium tetrahydroborate (NaBH4, commonly called sodium borohydride) in diglyme as a solvent, 2NaBH4 + I2 → B2H6(g) + 2NaI + H2(g), or by reaction of a solid borohydride (i.e., a salt containing the BH4− ion) with an anhydrous acid, 2NaBH4 + 2H3PO4 → B2H6(g) + 2NaH2PO4 + 2H2(g).
The commercially available borohydrides, which are also important owing to their wide use as inorganic reducing agents, are the most commercially significant series of borane derivatives and the primary starting materials for preparing boranes on both a laboratory and an industrial scale. The stereospecific hydroboration reaction mentioned above, 3RCH=CH2 + 1/2B2H6 → B(CH2CH2R)3 (where R is an alkyl group), nearly quantitatively yields organoboranes, which in turn can yield various organic compounds such as the alkane corresponding to the initial alkene or the primary alcohol.George B. Kauffman
INTRODUCTION TO SYNTHESES
(mostly from Cassie Carter - with her kind permission)
- What is a synthesis?
Two types of syntheses
Standards for synthesis essays
How to write synthesis essays
Techniques for developing synthesis essays
Thesis statements, introductions, conclusions, and quotations
WHAT IS A SYNTHESIS?
A synthesis is a written discussion that draws on one or more sources. It follows that your ability to write syntheses depends on your ability to infer relationships among sources - essays, articles, fiction, and also nonwritten sources, such as lectures, interviews, observations. This process is nothing new for you, since you infer relationships all the time - say, between something you've read in the newspaper and something you've seen for yourself, or between the teaching styles of your favorite and least favorite instructors. In fact, if you've written research papers, you've already written syntheses. In an academic synthesis, you make explicit the relationships that you have inferred among separate sources.
The skills you've already been practicing in this course will be vital in writing syntheses. Clearly, before you're in a position to draw relationships between two or more sources, you must understand what those sources say; in other words, you must be able to summarize these sources. It will frequently be helpful for your readers if you provide at least partial summaries of sources in your synthesis essays. At the same time, you must go beyond summary to make judgments - judgments based, of course, on your critical reading of your sources - as you have practiced in your reading responses and in class discussions. You should already have drawn some conclusions about the quality and validity of these sources; and you should know how much you agree or disagree with the points made in your sources and the reasons for your agreement or disagreement.
Further, you must go beyond the critique of individual sources to determine the relationship among them. Is the information in source B, for example, an extended illustration of the generalizations in source A? Would it be useful to compare and contrast source C with source B? Having read and considered sources A, B, and C, can you infer something else - D (not a source, but your own idea)?
Because a synthesis is based on two or more sources, you will need to be selective when choosing information from each. It would be neither possible nor desirable, for instance, to discuss in a ten-page paper on the battle of Wounded Knee every point that the authors of two books make about their subject. What you as a writer must do is select the ideas and information from each source that best allow you to achieve your purpose.
Your purpose in reading source materials and then in drawing upon them to write your own material is often reflected in the wording of an assignment. For example, your assignment may ask that you evaluate a text, argue a position on a topic, explain cause and effect relationships, or compare and contrast items. While you might use the same sources in writing an argumentative essay as your classmate uses in writing a comparison/contrast essay, you will make different uses of those sources based on the different purposes of the assignments. What you find worthy of detailed analysis in Source A may be mentioned only in passing by your classmate.
USING YOUR SOURCES
Your purpose determines not only what parts of your sources you will use but also how you will relate them to one another. Since the very essence of synthesis is the combining of information and ideas, you must have some basis on which to combine them. Some relationships among the material in you sources must make them worth sythesizing. It follows that the better able you are to discover such relationships, the better able you will be to use your sources in writing syntheses. Your purpose in writing (based on your assignment) will determine how you relate your source materials to one another. Your purpose in writing determines which sources you use, which parts of them you use, at which points in your essay you use them, and in what manner you relate them to one another.
TWO TYPES OF SYNTHESES
THE ARGUMENT SYNTHESIS: The purpose of an argument synthesis is for you to present your own point of view - supported, of course, by relevant facts, drawn from sources, and presented in a logical manner. The thesis of an argumentative essay is debatable. It makes a proposition about which reasonable people could disagree, and any two writers working with the same source materials could conceive of and support other, opposite theses.
STANDARDS FOR SYNTHESIS ESSAYS
2. Keep in mind that original thought and insightful analysis are required for a 4.0, 3.5, or 3.0 paper; 2.5 and below evaluations tend not to present original ideas.
3. A 4.0, 3.5, or 3.0 paper will create a "dialogue" between the essay author's ideas and her sources, and also among the sources themselves. 2.5 and below evaluations will often summarize one point at a time, with the essay author's idea stated at the end. If you imagine a synthesis essay as a room in which the synthesis writer is joined by the authors of her/his sources, the 4.0, 3.5, or 3.0 essay has everyone engaged in conversation or debate, with everyone commenting on (or arguing against) each other's ideas directly. In the 2.5 and below essay, each person in the room stands up in turn, gives a speech, and sits down, with little or no question and answer period in between or afterward.
4. Take special care to address your audience in an appropriate manner. Make sure you establish your credibility on the subject and that you provide sufficient information to make your argument (thesis) convincing.
- 5. Organize your paper logically:
- A. State your thesis clearly and make sure that it reflects the focus of your essay.
- B. Make sure your main points are clearly stated (use topic sentences), and connect each point to your thesis as explicitly as possible.
- C. Divide paragraphs logically.
- D. Provide appropriate transitions both within and between paragraphs.
7. Select words precisely. When in doubt, use a dictionary!
8. Make sure sentences are clear and unambiguous. Avoid passive voice. Double-check to see that sentences are adequately varied in length and style, and that there are no fragments or run-ons. Also proofread carefully to correct any other sentence errors.
9. Proofread carefully to identify and correct mechanical errors, such as errors in plurals or possessives, subject-verb agreement, shifts in verb tense or person ("you"), comma errors, spelling errors, and so on.
10. Quadruple check your MLA documentation. Are your parenthetical citations correct? Is your Works Cited list correct according to MLA style, and does it include all sources cited in your essay?
11. Be sure to give your essay a descriptive and attention-getting title (NOT "Synthesis," for goodness sake!!!).
12. Make sure your essay is formatted correctly and posted to your web site correctly.
HOW TO WRITE SYNTHESIS ESSAYS
- Consider your purpose in writing. Read the topic assignment carefully. What are you trying to accomplish in your essay? How will this purpose shape the way you approach your sources?
- Select and carefully read your sources, according to your purpose. Re-read the sources, mentally summarizing each. Identify those aspects or parts of your sources that will help you in fulfilling your purpose. When rereading, label or underline the passages for main ideas, key terms, and any details you want to use in the synthesis.
- Formulate a thesis. Your thesis is the main idea that you want to present in your synthesis. It must be expressed as a complete sentence and include a statement of the topic and your assertion about that topic. Sometimes the thesis is the first sentence, but more often it is the final sentence of the first paragraph.
- Decide how you will use your source material and take notes. How will the information and the ideas in your sources help you to fulfill your purpose? Re-read your sources and write down the information from your sources that will best develop and support your thesis.
- Develop and organizational plan, according to your thesis. (See Techniques for Developing Synthesis Essays immediately below.) How will you arrange your material? It is not necessary to prepare a formal outline, but you should have some plan in mind that will indicate the order in which you will present your material and that will indicate the relationships among your sources.
- Write the first draft of your synthesis, following your organizational plan. Be flexible with your plan, however, and allow yourself room to incorporate new ideas you discover as you write. As you discover and incorporate new ideas, re-read your work frequently to ensure that your thesis still accounts for what follows and that what follows still logically supports your thesis.
- Document your sources. Use MLA-style in-text citations and a Works Cited list to credit your sources for all material you quote, paraphrase, or summarize. For example, if I wanted to note in my essay the difference between name-calling and argumentum ad hominem as personal forms of attack, I would credit the article on "Politics: The Art of Bamboozling" fromWARAC by offering a citation that includes the author's last name and the exact page number where she discussed this notion (Cross 302). At the end of the essay, I would have a complete bibliographic citation for the "Politics" article.
- Revise your synthesis. Insert transitional words and phrases where necessary. Integrate all quotations so they flow smoothly within your own sentences. Use attribution phrases to distinguish between your sources' ideas and your own ideas. Make sure the essay reads smoothly, logically, and clearly from beginning to end. Check for grammatical correctness, punctuation, and spelling.
TECHNIQUES FOR DEVELOPING SYNTHESIS ESSAYS
Summary can be useful - and sophisticated - if handled judiciously, selectively, and in combination with other techniques. At some time you may need to summarize a crucial source in some detail. At another point, you may wish to summarize a key section or paragraph of a source in a single sentence. Try to anticipate what your reader needs to know at any given point of your paper in order to comprehend or appreciate fully the point you are making.
EXAMPLE OR ILLUSTRATION: At one or more points in your paper, you may wish to refer to a particularly illuminating example or illustration from your source material. You might paraphrase this example (i.e., recount it, in some detail, in your own words), summarize it, or quote it directly from your source. In all these cases, of course, you would properly credit your source.
TWO (OR MORE) REASONS: The "two reasons" approach can be an extremely effective method of development. You simply state your thesis, then offer reasons why the statement is true, supported by evidence from your sources. You can advance as many reasons for the truth of your thesis as needed; but save the most important reason(s) for last, because the end of the paper is what will remain most clearly in the reader's mind.
STRAWMAN: When you use the strawman technique, you present an argument against your thesis, but immediately afterward you show that this argument is weak or flawed. The advantage of this technique is that you demonstrate your awareness of the other side of the argument and show that you are prepared to answer it. The strawman argument first presents an introduction and thesis, then the main opposing argument, a refutation of the opposing argument, and finally a positive argument.
CONCESSION: Like the strawman, the concession technique presents the opposing viewpoint, but it does not proceed to demolish the opposition. Instead, it concedes that the opposition has a valid point but that, even so, the positive argument is the stronger one. This method is particularly valuable when you know your reader holds the opposing view.
COMPARISON AND CONTRAST: Comparison and contrast techniques enable you to examine two subjects (or sources) in terms of one another. When you compare, you consider similarities. When you contrast, you consider differences. By comparing and contrasting, you perform a multifaceted analysis that often suggests subtleties that otherwise might not have come to your attention.
To organize a comparison/contrast analysis, you must carefully read sources in order to discover significant criteria for analysis. A criterion is a specific point to which both of your authors refer and about which they may agree or disagree. The best criteria are those that allow you not only to account for obvious similarities and differences between sources but also to plumb deeper, to more subtle and significant similarities and differences. There are two basic formulas for comparison/contrast analysis:
|I. Introduce essay, state thesis||I. Introduce essay, state thesis|
|II. Summarize passage A||II. Introduce Criterion 1|
|A. View on Criterion I||A. Passage A's viewpoint|
|B. View on Criterion 2||B. Passage B's viewpoint|
|III. Summarize passage B||III. Introduce Criterion 2|
|A. View on Criterion 1||A. Passage A's viewpoint|
|B. View on Criterion 2||B. Passage B's viewpoint|
|IV. Discussion and conclusion||IV. Discussion and conclusion|