Drawing Lewis Structures

Since nucleophilic atoms have nonbonding electrons they can be identified by inspection of Lewis structures. Draw Lewis structures of triraethylamine, methyl fluoride, and phenol. Draw all nonbonding electron pairs and identify all nucleophilic atoms. 

Now, if you were a benchwarmer like me, there was never a symbol on the board for you only the players who actually play in the game earn one of coach s Xs. The same is true when drawing electrons on a Lewis structures Only the electrons that can participate in chemical bonding, the valence electrons, earn a spot on the Lewis structure drawings. The electrons that are in the inner shells of an atom don t play a role in bonding, so they are ignored. 

Solution to 29a 1 Our first attempt at a Lewis structure (drawing the atoms with the hydrogens on the outside of the molecule) shows that carbon is the only atom that does not form the needed number of bonds. 

Complete each Lewis structure, draw all important resonance structures, predict a value for the bond angles requested, and explain your reasoning. 

Below are four resonance structures of the eonjugate base of para-nitrophenol with the nitro group drawn as a full Lewis structure. Draw a fifth resonance structure that shows that nitro withdraws electrons from the ring via resonance effects. 

It is not possible to draw unambiguous Lewis structures for excited states of the sort that are so useful in depicting ground-state chemistry. Instead, it is common to asterisk the normal carbonyl structure and provide information about the nature and multiplicity of the excited state ... 

Is the double bond incorporated into allene significantly shorter, significantly longer or about the same length as the bond in ethene Draw a Lewis structure for allene to justify your conclusion. 

Draw a Lewis structure for singlet methylene, CH2 (all the electrons in singlet methylene are spin-paired). Ho many electrons remain after all bonds have been formei Where are the extra electrons located, in the plane the molecule or perpendicular to the plane Examine t highest-occupied molecular orbital (HOMO) of methyle to tell. 

Draw Lewis structures for allyl cation. Where is the positive charge Examine atomic charges as well as the electrostatic potential map for localized and delocalized forms of allyl cation. Which carbon (s) carries the charge in each ... 

What happens to electrons which are left over after all bonds have been formed Do they associate with individual atoms or are they spread uniformly throughout the molecule Draw a Lewis structure for trimethylamine. How many electrons are needed to make bonds How many are left over Where are they Display the highest-occupied molecular orbital (HOMO) for trimethylamine. Where is it located ... 

Examine the HOMO-2 forphenylisocyanide. Is it directly involved in any o or K bonds If so, which bonds If not, describe where it is located. Draw a Lewis structure for the molecule which is consistent with your result. 

Draw Lewis structures for methyl anion, ammonia and hydronium cation. How many electrons are left over in each after all bonds have been made Display and compare electron density surfaces for methyl anion, ammonia and hydronium cation. Which is the smallest molecule Which is the largest Rationalize your observation. (Hint Compare the number of electrons in each molecule, and the nuclear charge on the central atom in each molecule.)... 

Based on its structure and valence electron count, draw a Lewis structure or series of Lewis structures for diborane Examine the bond density surface. Does it substantiate 01 refute your speculation ... 

Draw a Lewis structure (or series of Lewis structures) foi 2-norbornyl cation which adequately describes its geometry, charge distribution and bond density surface, Relate this structure to your description of 3-methyl-1-butyl cation. 

Compare atomic charges and electrostatic potential maps for imidazole NH protonated and imidazole Nprotonated. In which ion is the positive charge more delocalized Compare carbon-nitrogen bond distances in each ion to those in imidazole as a standard. Are these distances consistent with the bonding patterns shown above for each ion Draw whatever Lewis structures are needed to describe each ion s geometry and charge distribution. 

Does your transition state drawing look more like a sing Lewis structure or a resonance hybrid If the latter, whi resonance contributors must you combine to generate a of the features of this hybrid ... 

Nucleophiles can also act as acids and bases, and this behavior substantially alters their nucleophilicity. At pH 5, trimethylamine exists mainly as its conjugate acid, trimethylammonium cation. First draw a Lewis structure, and then examine the electrostatic potential for trimethylammonium ion. On the basis of the map, which is the better nucleophile, the cation or the corresponding neutral amine At pH 12, phenol exists mainly as its conjugate base, phenoxide anion. First draw a Lewis structure (or series of Lewis structures), and then examine the electrostatic potential map for phenoxide anion. Which is the better nucleophile, phenoxide or phenol ... 

Draw the Lewis structure of each carbocation (show all formal charges). Do these structures provide any indication of which carbocation will form most readily Explain. Examine the electrostatic potential map of each carbocation. Which carbocation shows the greatest localization of positive charge Which shows the greatest delocalization of charge Where does the positive charge go in the most delocalized ion Do these observations provide any indication of which caibocation will form most readily ... 

At which point in the initial addition is there the greatest separation of charge Draw Lewis structures for C4H9 and Cl that show all nonbonding electrons and formal charges. 

Draw Lewis structures for the possible carbocations resulting from protonation of the double bond in 3-methyl-1-butene, and decide which is favored. (Check your result using available energy data for C5H11 carbocations.) What would be the product of bromide addition to the more stable cation Is this the observed product ... 

The first step in the addition of an electrophile such as HBr to an alkyne involves protonation and subsequent formation of an intermediate vinyl cation. Where does propyne protonate Compare energies of 1-methylvinyl and 2-methylvinyl cations. Which is more stable Why Measure CC bond distance in the more stable cation. Does the cation incorporate a full triple bond (as in propyne) or a double bond (as in propene). Examine atomic charges and electrostatic potential maps to locate the positive charge in the two cations. Is the more stable ion the one in which the charge is better delocalized Use the charges together with information about the ions geometry to draw Lewis structures (or a series of Lewis structures) for 1-methylvinyl and 2-methylvinyl cations. 

Obtain the energies of the different possible carbanions alleyne-H+). Which one is most stable Does it correspond to removal of the most electron-poor proton Examine the geometry and atomic charges of the favored carbanion. Where is the negative charge Draw the Lewis structure of this ion. Predict the structure of the Sn2 product. 

Phenol has different chemical properties from those of typical alcohols. Display the electrostatic potential map for phenol. Does this suggest that phenol is likely to be a stronger or weaker acid than any of the compounds discussed above Compare the electrostatic potential map for 4-nitrophenol to that for phenol. What effect does substitution by nitro have on acid strength Explain your result by considering charge delocalization in the conjugate base. Draw all reasonable Lewis structures for phenoxide anion and for 4-nitrophenoxide anion. Which is more delocalized Is this consistent with experimental pKa s ... 

Examine electrostatic potential maps for potassium hydride and hydrogen chloride. How are they similar and how are they different (Focus on whether the molecules are polar or nonpolar (compare dipole moments), and on the electronic character of hydrogen.) Draw the ionic Lewis structure that is most consistent with each electrostatic potential map. Does each atom have a filled valence shell ... 

In order to predict the structure of the product, you must identify the factors that will tend to favor selective ketal formation. Consider selective carbonyl protonation first. Obtain energies and atomic charges, and display electrostatic potential maps of the alternative protonated ketones (protonated ketone A, protonated ketone B). Identify the more stable isomer. Compare geometries and draw whatever Lewis structures are needed to account for your data. Why is one isomer more stable than the other Is the more stable isomer also that in which the positive charge is better delocalized Will the more stable isomer undergo nucleophilic attack more or less easily than the other Explain. 

Draw a Lewis structure for cyclohexenone that involves charge separation for the most polar bond. Then, draw a Lewis structure that will delocalize one or both charges. Next, examine the actual geometry of cyclohexenone. Are the bond distances consistent with the Lewis structure shown above, or have they altered in accord with your alternative (charge separated) Lewis structure (Structures for cyclohexene and cyclohexanone are available for reference.)... 

Compare and contrast the electrostatic potential map of a typical detergent with that of a typical soap (stearate). Which part of each molecule will be most water soluble (hydrophilic) Draw a Lewis structure that describes each molecule s water-soluble group (make sure you indicate all necessary formal charges and lone pairs). Which part(s) of each molecule will be most grease soluble (lipophilic) What kinds of atoms and bonds are found in these groups ... 

How many different enolates may arise from deprotonation of 2,4-pentanedione Draw Lewis structures for each, and predict which is likely to be the most stable. Check your conclusions by examining the energies of the different possible enolates (enolate A, B...). Is the most stable enolate that derived from deprotonation of the most electron-poor hydrogen Compare the electrostatic potential maps of the anions with each other and with your Lewis structures. Revise your drawings to be consistent with the maps. Why is one of the enolates preferred over the others ... 

Examine the geometry of planar corannulene. Are all of its six-membered rings the same If so, draw a Lewis structure whieh best represents the molecule. If not, draw one or more Lewis structures as appropriate. 

Draw a Lewis structure (or a series of Lewis structures) for nitrobenzenium ion. Where is the positive charge Examine the electrostatic potential map for nitrobenzenium ion. Where would you expect electron-donor substituents to have the greatest stabilizing effect (consider meta and para positions only) Which is the more stable, meta or para-nitrotoluenium ion (intermediates in nitration of toluene) Compare electrostatic potential maps to that for nitrobenzenium ion. Does your result suggest that methyl acts as an electron donor ... 

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