Electrostatic potential maps hydrogen

The interaction between these molecules is illustrated by using three different representations ball and stick, line representation, and electrostatic potential maps. Hydrogen bonding between CHCI3 (chloroform) and (CH3)2CO (acetone) molecules produces forces of attraction between unlike molecules that exceed those between like molecules. 

The electrostatic potential map of hydrogen fluoride (HF) was shown in the preceding section and IS repeated here Compare it to the electrostatic po tential map of lithium hydride (LiH)... 

Figure 2 4 uses electrostatic potential maps to show this build up of electron den sity m the region between two hydrogen atoms as they approach each other closely enough for their orbitals to overlap... 

Examine the electrostatic potential map of H3B THE (borane-tetrahydrofuran complex) on Learning By Modeling How does the electrostatic potential of the hydrogens bonded to boron dif fer from the potential of the hydrogens of the tetrahydrofuran ring" ... 

Lone pair donation from the hydroxyl oxygen makes the carbonyl group less elec trophilic than that of an aldehyde or ketone The graphic that opened this chapter is an electrostatic potential map of formic acid that shows the most electron rich site to be the oxygen of the carbonyl group and the most electron poor one to be as expected the OH hydrogen... 

As useful as molecular models are, they are limited in that they only show the location of the atoms and the space they occupy. Another important dimension to molecular structure is its electron distribution. We introduced electrostatic potential maps in Section 1.5 as a way of illustrating charge distribution and will continue to use them throughout the text. Figure 1.6(d) shows the electrostatic potential map of methane. Its overall shape is similar to the volume occupied by the space-filling model. The most electron-rich regions are closer to carbon and the most electron-poor ones are closer to the hydrogens. 

Problem 1.8 concerned the charge distribution in methane (CH4), chloromethane (CH3CI), and methyllithium (CH3Li). Inspect molecular models of each of these compounds, and compare them with respect to how charge is distributed among the various atoms (carbon, hydrogen, chlorine, and lithium). Compare their electrostatic potential maps. 

FIGURE 2.4 Valence bond picture of bonding in H2 as illustrated by electrostatic potential maps. The Is orbitals of two hydrogen atoms overlap to give an orbital that contains both electrons of an H2 molecule. 

The S—H bond is less polai than the O—H bond, as is cleaiTy seen in the electrostatic potential maps of Figure 15.7. The decreased polarity of the S—H bond, especially the decreased positive character of the proton, causes hydrogen bonding to be absent in thiols. Thus, methanethiol (CH3SH) is a gas at room temperature (bp 6°C), whereas methanol (CH3OH) is a liquid (bp 65°C). 

Next, examine electrostatic potential maps for the same set of compounds. Focus your attention on the value of the potential around hydrogen. For which molecule is it most positive For which is it most negative Is there a correlation between the value of the potential and the difference in electronegativities Plot charge on hydrogen (vertical axis) vs. difference in electronegativities (horizontal axis). Is there a correlation ... 

First, attempt to identify the most acidic hydrogen in the starting material, based on hybridization or on the nature of neighboring atoms. Explain your rationale. Next, examine the electrostatic potential map for starting material alkyne). Which hydrogen appears to be most electron poor Is this the one that you predicted What makes this hydrogen more electron poor than the others ... 

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 ... 

Both NaH and KH are used to deprotonate alcohols. KH is more reactive than NaH. Compare atomic charges and electrostatic potential maps of potassium hydride and sodium hydride. For which is the hydrogen more negatively charged Which should be the better source of hydride ... 

Experimental reactivity patterns are based on solution behavior which are influenced by interactions between solvent and reacting molecules (especially ions). Compare electrostatic potential maps of 2-methyl-2-propyl cation and dimethylhydroxy cation. Identify sites that might form strong hydrogen bonds with water. Which ion will be better stabilized by its interaction with water ... 

Compare electrostatic potential maps for propane, acetone and 2,4-pentanedione, and identify the most positively-charged acidic hydrogen(s) in each. Is there a correlation between electrostatic potential and pK (see table at right) ... 

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 atomic charges and display the electrostatic potential map for 2,7-octadione. Are you able to say which hydrogens (at Ci or at C3) are more likely to be abstracted by base, and conclude which is the kinetically-favored enolate Which enolate (2,7-octadione, Cl enolate or C3 enolate) is the lower in energy What do you conclude is the thermodynamically-favored enolate Is this also the enolate in which the negative charge is better delocalized Compare electrostatic potential maps to tell. 

Examine atomic charges and display electrostatic potential maps for ammonium and trimethylammonium ions (protonated ammonia and trimethylamine, respectively). How many acidic hydrogens are there in each Assuming that solvent coordinates to acidic hydrogens, how many solvation sites are there in each ... 

The previous calculation assumed that the solvation energy of ammonium was equal the solvation energy of a single water molecule times the number of water binding sites. Is this a valid assumption Compare the electrostatic potential maps of ammonium ion and ammonium ion+water. For which are the exposed hydrogens more acidic Did the calculation underestimate or overestimate the difference in solvation energies ... 

Examine atomic charges as well as the electrostatic potential map of ascorbic acid. Which hydrogen(s) is likely to be most acidic ... 

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