Benzene drawing

Pyridine is a flat, hexagonal molecule with bond angles of 120°. It undergoes substitution rather than addition and generally behaves like benzene. Draw a picture of the 7T orbitals of pyridine to explain its properties. Check your answer by looking ahead to Section 15.7. 

The articles by J. R. Anderson, J. H. Sinfelt, and R. B. Moyes and P. B. Wells, on the other hand, deal with a classical field, namely hydrocarbons on metals. The pattern of modem wTork here still very much reflects the important role in the academic studies of deuterium exchange reactions and the mechanisms advanced by pioneers like Horiuti and Polanyi, the Farkas brothers, Rideal, Tw igg, H. S. Taylor, and Turkevich. Using this method, Anderson takes ultrathin metal films with their separated crystallites as idealized models for supported metal catalysts. Sinfelt is concerned with hydrogcnolysis on supported metals and relates the activity to the percentage d character of the metallic bond. Moyes and Wells deal with the modes of chemisorption of benzene, drawing on the results of physical techniques and the ideas of the organometallic chemists in their discussions. 

In the chapter, we established that electron-withdrawing groups direct meta. Among such reactions is the nitration of trifluoromethyl benzene. Draw out the detailed mechanism for this reaction and also for a reaction that does not happen—the nitration of the same compound in the para position. Draw all the delocalized structures of the intermediates and convince yourself that the intermediate for para substitution is destabilized by the CF3 group while that for meta substitution is not. 

An important observation supporting the need for resonance in the LE model is that there are only three different structures of dichlorobenzene (C6H4C12). How does this fact support the need for the concept of resonance Borazine (B3N3H6) has often been called inorganic benzene. Draw Lewis structures for borazine. Borazine is a six-membered ring of alternating boron and nitrogen atoms. 

Propose a synthesis of 4-chIoro-l-nitro-2 propyibenzene from benzene. Draw the target molecule and identify its substituents Vj... 

This time, as a result of the cyclic nature of this molecule, it is possible to draw three new double bonds, and not just two. This arises, because what were the two unpaired electrons that were at the ends of the chain, are now adjacent to each other and so may interact to form the third bond. Superficially, the new molecule looks the same as the old one, except that the double bonds have moved one position around the ring. However, even though this looks like a small difference, in fact it belies the fact that the cyclic version of the triene has completely different properties from its linear cousin. This cyclic triene molecule is benzene. Draw a representation for the time-averaged redistribution of the electrons present in these three double bonds within this cyclic molecule. 

For each reaction one molecule of xylene would be generated as well as one molecule of benzene. Draw the different transition states that you beheve would lead to the formation of the different xylene isomers. Based on these transition states might you expect to observe transition state selectivity and could you rationalize the selectivity of ZSM-5 for p-xy lene based on that What are the pore dimensions ofZSM-5 ... 

Borazine (BsNsHg) has often been called inorganic benzene. Draw Lewis structures for borazine. Borazine is a six-membered ring of alternating boron and nitrogen atoms. 

A final note about nomenclature is in order for benzene. Drawing a benzene ring occupies a lot of space, so a shorthand representation is used in many structures. In 96, the shorthand symbol Ph is used to represent a phenyl substituent. In the older chemical literature, the Greek symbol ( ) (phi) was sometimes used. The Ph representation will be used often in this book, and compound 96 is named 5-chloro-2,6-diphenyloct-2-ene. 

Alternatively, any or all three files for benzene, cyclohexene, and cyclohexane can be generated using the draw option of PCMODEL. Either way, the cyclohexene file is... 

Compute the IIMO eigenvalues for benzene and draw its energy level diagram. 16. Draw the energy level diagram for pyrrole. 

B. Dc.war benzene (2) exists as cis and tram isomers. Draw struetures of the two f onris. construct the appropriate input files and determine the c.is-iram isomerization energy of (2). 

Cholestenone. Place a mixture of 1 0 g. of purified cholesterol and 0-2 g. of cupric oxide in a test-tube clamped securely at the top, add a fragment of Dry Ice in order to displace the air by carbon dioxide, and insert a plug of cotton wool in the mouth of the tube. Heat in a metal bath at 300-315° for 15 minutes and allow to cool rotate the test-tube occasionally in order to spread the melt on the sides. Warm with a few ml. of benzene and pour the black suspension directly into the top of a previously prepared chromatographic column (1) rinse the test-tube with a little more benzene and pour the rinsings into the column. With the aid of shght suction (> 3-4 cm. of mercury), draw the solution into the alumina column stir the top 0 -5 cm. or so with a stout copper wire to... 

A 1968 German stamp com bines a drawing of the struc ture of benzene with a portrait of Kekule... 

Oxazoles give acylamino ketones (158) by acid-catalyzed ring scission, although they are somewhat more stable than furans. The oxazole ring is also moderately stable to alkali (74AHCU7)99) as expected, reaction with hydroxide ions is facilitated by electron-with-drawing substituents and fused benzene rings. 

The crystallization of wax from lubricating oil fractions makes better oil. This is done by adding a solvent (often a mixture of benzene and methyl ethyl ketone) to the oil at a temperature of about -5 F. The benzene keeps the oil in solution and maintains fluidity at low temperature the methyl ethyl ketone acts to precipitate the wax. Rotary filters deposit the wax crystals on a sp woven cloth stretched over a perforated cylindrical drum. A vacuum in the drum draws the oil through the perforations. The wax crystals are removed from the cloth by metal scrapers and ol vent-washed to remove oil followed by solvent distillation to remove oil for reuse. 

You may also want to draw on the benzene optimization we performed in Chapter 3. 

Measure the carbon-carbon bond length in benzene. Would you describe it as a single bond, a double bond, or somewhere in between Draw whatever resonance contributors are needed to justify your conclusion. 

Draw the two resonance contributors that are needed to describe each transition state. Identify all partial carbon-carbon double bonds () and measure their distances. Are these values like that found in benzene, or do transition states have their own characteristic partial double bond... 

Compare atomic charges and electrostatic potential maps for the three cations. For each, is the charge localized or delocalized Is it associated with an empty a-type or Tt-type orbital Examine the lowest-unoccupied molecular orbital (LUMO) of each cation. Draw all of the resonance contributors needed for a complete description of each cation. Assign the hybridization of the C" atom, and describe how each orbital on this atom is utilized (o bond, n bond, empty). How do you explain the benzene ring effects that you observe ... 

Examine the geometry of methylbenzyne. Measure carbon-earbon distances. Which 7C bonds are deloealized and whieh are localized Is there really a triple bond (Compare bond distance to triple bond in hexa-l,5-dien-3-yne and to partial double bonds in benzene). Are you able to draw a single Lewis structure whieh adequately represents the geometry of the molecule ... 

Draw and compare Lewis structures for benzene and pyridine. How many 7C electrons does each molecule have Where are the most accessible electrons in each Display the electrostatic potential map for pyridine and compare it to the corresponding map for benzene. Would you expect electrophilic attack on pyridine to occur analogously to that in benzene If so, should pyridine be more or less susceptible to aromatic substitution than benzene If not, where would you expect electrophilic attack to occur Explain. 

Draw the most important resonance contributors for nitrobenzene (include all of the contributors needed to explain for the variation in electrostatic potential, charge and chemical shift relative to benzene). Do these resonance contributors account for the different behavior of 6meta and 6paia Explain. 

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