Structure and Bonding

Question: Which of the given resonance structures (A, B, or C) contributes most to the resonance hybrid? Which contributes the least?

Question: Consider the compounds and ions with curved arrows drawn below. When the curved arrows give a second valid resonance structure, draw the resonance structure. When the curved arrows generate an invalid Lewis structure, explain why the structure is unacceptable.

                                                      a.

                                                       b.

                                                        c.

                                                         d.

Question: Predict all bond angles in each compound.

$$\begin{gathered} \mathbf{a}\mathbf{.}\mathbf{ }{\mathbf{CH}}_{\mathbf{3}}\mathbf{Cl} \\ \mathbf{b}\mathbf{.}\mathbf{ }{\mathbf{NH}}_{\mathbf{2}}\mathbf{OH} \\ \mathbf{c}\mathbf{.}\mathbf{ }{\mathbf{CH}}_{\mathbf{2}}\mathbf{=}{\mathbf{NCH}}_{\mathbf{3}} \\ \mathbf{d}\mathbf{.}\mathbf{ }\mathbf{CH}\mathbf{\equiv }{\mathbf{CCH}}_{\mathbf{2}}\mathbf{OH} \end{gathered}$$

e.

Question: Predict the geometry around each highlighted atom

                                   a.

                                    b.

                                    c.

                                     d.

                                     e.

Question: Draw in all the carbon and hydrogen atoms in each molecule.

                                                  a.

                                                 b.

                                                 c.

                                                d.

Question: Convert each molecule into a skeletal structure.

                                          a.

                                           b.

                                    c.

                                                     d.

Question: Convert the following condensed formulas into skeletal structures:

$$\begin{gathered} \mathbf{a}\mathbf{.}\mathbf{ }{\mathbf{CH}}_{\mathbf{3}}{\mathbf{CONHCH}}_{\mathbf{3}\mathbf{ }\mathbf{ }\mathbf{ }\mathbf{ }\mathbf{ }\mathbf{ }\mathbf{ }\mathbf{ }\mathbf{ }\mathbf{ }\mathbf{ }\mathbf{ }\mathbf{ }\mathbf{ }\mathbf{ }\mathbf{ }}\mathbf{c}\mathbf{.}\left({\mathrm{CH}}_3\right)\mathbf{COH}\mathbf{ }\mathbf{ }\mathbf{ }\mathbf{ }\mathbf{ }\mathbf{ }\mathbf{ }\mathbf{ }\mathbf{e}\mathbf{.}{\mathbf{CH}}_{\mathbf{3}}{\mathbf{COCH}}_{\mathbf{2}}{\mathbf{CO}}_{\mathbf{2}}\mathbf{H} \\ \mathbf{b}\mathbf{.}\mathbf{ }{\mathbf{CH}}_{\mathbf{3}}{\mathbf{COCH}}_{\mathbf{2}}\mathbf{Br}\mathbf{ }\mathbf{ }\mathbf{ }\mathbf{ }\mathbf{ }\mathbf{ }\mathbf{ }\mathbf{ }\mathbf{ }\mathbf{ }\mathbf{ }\mathbf{d}\mathbf{.}{\mathbf{CH}}_{\mathbf{3}}\mathbf{COCl}\mathbf{ }\mathbf{ }\mathbf{ }\mathbf{ }\mathbf{ }\mathbf{ }\mathbf{ }\mathbf{ }\mathbf{ }\mathbf{ }\mathbf{f}\mathbf{.}\mathbf{ }{\mathbf{HO}}_{\mathbf{2}}\mathbf{CCH}\left(\mathrm{OH}\right){\mathbf{CO}}_{\mathbf{2}}\mathbf{H} \end{gathered}$$

Question: Draw in all the hydrogen atoms and nonbonded electron pairs in each ion.

                                               a.

                                                 b.

                                                  c.

                                                  d.

                                                  e.

Question: Predict the hybridization and geometry around each highlighted atom.

                                a.

                                b.

                                c.

                                  d.

                                 e.

Question: What orbitals are used to form each highlighted bond? For multiple bonds, indicate the orbitals used in individual bonds.

                                        a.

                                           b.

                                           c.

Question: Ketene, ${\mathbf{CH}}_{\mathbf{2}}\mathbf{=}\mathbf{C}\mathbf{=}\mathbf{O}$ , is an unusual organic molecule that has a single carbon atom doubly bonded to two different atoms. Determine the hybridization of both C and the O in ketene. Then, draw a diagram showing what orbitals are used to form each bond (similar to Figures 1.10 and 1.11).

Question: Rank the following bonds in order of increasing bond length.

Question: Answer the following questions about compound A:

1. Label the shortest   single bond.
2. Label the longest   single bond.
3. Considering all the bonds, label the shortest   bond.
4. Label the weakest  bond.
5. Label the strongest   bond.
6. Explain why bond [1] and bond [2] are different in length, even though they are both  single bonds.

Question: Two useful organic compounds that contain Cl atoms are vinyl chloride $\left({\mathrm{CH}}_2=\mathrm{CH}-\mathrm{Cl}\right)$   and chloroethane $\left({\mathrm{CH}}_3{\mathrm{CH}}_2\mathrm{Cl}\right)$ . Vinyl chloride is the starting material used to prepare poly (vinyl chloride), a plastic used in insulation, pipes, and bottles. Chloroethane (ethyl chloride) is a local anesthetic. Why is the bond of vinyl chloride stronger than the bond in chloroethane?

Question: Use the symbols  and   to indicate the polarity of the highlighted bonds.

                                                   a.

                                                    b.

                                                      c.

Question: Label the polar bonds in each molecule. Indicate the direction of the net dipole (if there is one). 

$$\begin{gathered} \mathbf{a}\mathbf{.}\mathbf{ }{\mathbf{CHBr}}_{\mathbf{3}} \\ \mathbf{b}\mathbf{.}\mathbf{ }{\mathbf{CH}}_{\mathbf{3}}{\mathbf{CH}}_{\mathbf{2}}{\mathbf{OCH}}_{\mathbf{2}}{\mathbf{CH}}_{\mathbf{3}} \end{gathered}$$

c.

   d. 

Question: Anacin is an over-the-counter pain reliever that contains aspirin and caffeine. Answer the following questions about each compound:

a. What is the molecular formula?  

b. How many lone pairs are present on heteroatoms?

 c. Label the hybridization state of each carbon. 

d. Draw three additional resonance structures.

Question: Answer the following questions about acetonitrile $\left({\mathrm{CH}}_{3}C\equiv N\right)$ :

a. Determine the hybridization of both C and N atoms. 

b. Label all bonds as $\mathit{\sigma }$ or$\mathbf{\pi }$  .

c. In what type of orbital does the lone pair on N reside? 

d. Label all bonds as polar or nonpolar.

Question: Benzene is the simplest member of a whole class of compounds called aromatic hydrocarbons.

a. How is each carbon atom hybridized?

b. What is the geometry around each carbon atom? What is the overall geometry of the benzene ring? 

c. Follow the indicated curved arrow notation to draw a second resonance structure.

                                                                  

d. Benzene and other aromatic hydrocarbons are shown in Chapter 17 to be very stable. Offer an explanation.

Question: The principles of this chapter can be applied to organic molecules of any size. Answer the following questions about amoxicillin, an antibiotic from the penicillin family: 

a. Predict the hybridization and geometry around each highlighted atom.

 b. Label five polar bonds using the symbols  ${\mathbf{\delta }}^{\mathbf{+}}\mathbf{ }\mathbf{and}\mathbf{ }\mathbf{ }{\mathbf{\delta }}^{\mathbf{-}}$ . 

c. How many π bonds does amoxicillin have? Label them.  

d. Find a C- H bond containing a carbon atom having a hybrid orbital with 33% s character.

Question:

a. What is the hybridization of each N atom in nicotine? 

b. What is the geometry around each N atom? 

c. In what type of orbital does the lone pair on each N atom reside?

d. Draw a constitutional isomer of nicotine. 

e. Draw a resonance structure of nicotine.

Question: Stalevo is the trade name for a medication used in Parkinson’s disease, containing L-dopa, carbidopa, and entacapone.

 a. Draw a Lewis structure for entacapone.

 b. Which C–C bond in entacapone is the longest?

 c. Which C–C single bond is the shortest?

 d. Which C–N bond is the longest? 

 e. Which C–N bond is the shortest?

 f. Use curved arrows to draw a resonance structure that is an equal contributor to the resonance hybrid. 

 g. Use curved arrows to draw a resonance structure that is a minor contributor to the resonance hybrid.

Question:  $\stackrel{\mathbf{+}}{\mathbf{C}}{\mathbf{H}}_{\mathbf{3}\mathbf{ }}\mathbf{and}\mathbf{ }\stackrel{\mathbf{-}}{\mathbf{C}}{\mathbf{H}}_{\mathbf{3}}$ are two highly reactive carbon species.

1. What is the predicted hybridization and geometry around each carbon atom?
2. Two electrostatic potential plots are drawn for these species. Which ion corresponds to which diagram and why?

                                                             A.

                                                              B.

Question: The N atom in ${\mathbf{CH}}_{\mathbf{3}}{\mathbf{CONH}}_{\mathbf{2}}$   (acetamide) is ${\mathbf{sp}}^{\mathbf{2}}$  hybridized, even though it is surrounded by four groups. Using this information, draw a diagram that shows the orbitals used by the atoms in the $\mathbf{-}{\mathbf{CONH}}_{\mathbf{2}}$ portion of acetamide, and offer an explanation as to the observed hybridization

Question: Use the observed bond lengths to answer each question. (a) Why is bond [1] longer than bond [2] (143 pm versus 136 pm)? (b) Why are bonds [3] and [4] equal in length (127 pm) and shorter than bond [2]?

Question: Draw at least ten more resonance structures for acetaminophen, the active pain reliever in Tylenol.

Question: When two carbons having different hybridizations are bonded together, the C-C bond contains a slight dipole. In a C_sp² - C_sp³ bond, what is the direction of the dipole? Which carbon is considered more electronegative?

Question: Draw all possible isomers having a molecular formula C₄H₈ that contains one π  bond.

Question: Use the principles of resonance theory to explain why carbocation A is more stable than carbocation B.

Question: The curved arrow notation introduced in Section 1.6 is a powerful method used by organic chemists to show the movement of electrons not only in resonance structures but also in chemical reactions. Since each curved arrow shows the movement of two electrons, following the curved arrows illustrates what bonds are broken and formed in a reaction. Consider the following three-step process: (a) Add curved arrows in Step [1] to show the movement of electrons. (b) Use the curved arrows drawn in Step [2] to identify the structure of X; X is converted in Step [3] to phenol and HCl.