Identify electrophiles (Lewis acids) and nucleophiles (Lewis bases), and write equations

The C O double bond has a dipole moment of about 2.4 D and a bond length of about 1.23 . (a) Calculate the amount of charge separation in this bond. (b) Use this information to evaluate the relative importance of the following two resonance contributors: O C R R C+ R R O (R is a general symbol for a carbon-containing group.)

The N F bond is more polar than the N H bond, but NF3 has a smaller dipole moment than NH3. Explain this curious result. NH3 NF3 m = 1.5 D m = 0.2 D

For each of the following compounds: 1. Draw the Lewis structure. 2. Show how the bond dipole moments (and those of any nonbonding pairs of electrons) contribute to the molecular dipole moment. 3. Estimate whether the compound will have a large, small, or zero dipole moment. (a) NH4 + (b) O3 (a) NH4 + has four polar NH bonds. These bonds are probably more polarized than a typical NH bond, because the N in NH4 + bears a formal positive charge. Nevertheless, these four polar bonds have a symmetric tetrahedral arrangement so they cancel each other. dipoles cancel net dipole = 0 +N H H H H (b) Ozone (O3) is an sp2 hybrid structure, with a lone pair on the central oxygen atom. Therefore, O3 must be bent. The resonance structures imply partial negative charges on the outer oxygens and a partial positive charge on the central oxygen. The lone pair on the central oxygen cancels part, but not all, of the vector sum of the two OO dipoles. The resulting net dipole is relatively small.

Two isomers of 1,2-dichloroethene are known. One has a dipole moment of 2.4 D; the other has zero dipole moment. Draw the two isomers, and explain why one has zero dipole moment. CHClCHCl 1,2-dichloroethene

Draw the hydrogen bonding that takes place between (a) two molecules of ethanol. (b) two molecules of propylamine. (c) a molecule of dimethyl ether and two molecules of water. (d) two molecules of trimethylamine and a molecule of water.

For each pair of compounds, circle the compound you expect to have the higher boiling point. Explain your reasoning. (a) (CH3)3CC(CH3)3 or (CH3)2CHCH2CH2CH(CH3)2 (b) CH3(CH2)6CH3 or CH3(CH2)5CH2OH (c) CH3CH2OCH2CH3 or CH3CH2CH2CH2OH (d) HOCH2(CH2)4CH2OH or (CH3)3CCH(OH)CH3 (e) (CH3CH2CH2)2NH or (CH3CH2)3N (f) NH or NH2

Circle the member of each pair that is more soluble in water. (a) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OCH}_{2} \mathrm{CH}_{3} \text { or } \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{3}\) (b) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OCH}_{2} \mathrm{CH}_{3} \text { or } \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{OH}\) (c) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{NHCH}_{3} \text { or } \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{3}\) (d) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH} \text { or } \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{OH}\)

Calculate the pH of the following solutions. (a) 5.00 g of HBr in 100 mL of aqueous solution (b) 1.50 g of NaOH in 50 mL of aqueous solution

Ammonia appears in Table 2-2 as both an acid and a conjugate base. (a) Explain how ammonia can act as both an acid and a base. Which of these roles does it commonly fill in aqueous solutions? (b) Show how water can serve as both an acid and a base. (c) Calculate \(K_a\) and \(pK_a\) for the hydronium ion, \(H_3O^+\). (d) Show how methanol (\(CH_3OH\)) can serve as both an acid and a base. Write an equation for the reaction of methanol with sulfuric acid.

Write equations for the following acidbase reactions. Use the information in Table 2-2 or Appendix 4 to predict whether the equilibrium will favor the reactants or the products. (a) HCOOH + -CN (b) CH3COO- + CH3OH (c) (CH3)2CHOH + NaNH2 (d) NaOCH3 + HCN (e) HCl + CH3CH2OH (f) H3O+ + CH3O(g) N H + OH (h) N H + COOH (i) SH CH + 3CH2O (j) CH3CH2OH + C C Na+

Ethanol, methylamine, and acetic acid are all amphoteric, reacting as either acids or bases depending on the conditions. ethanol CH3CH2OH methylamine CH3NH2 acetic acid CH3 C OH O (a) Rank ethanol, methylamine, and acetic acid in decreasing order of acidity. In each case, show the equation for the reaction with a generic base (B:-) to give the conjugate base. (b) Rank ethanol, methylamine, and acetic acid in decreasing order of basicity. In each case, show the equation for the reaction with a generic acid (HA) to give the conjugate acid.

For each of the following reactions, suggest which solvent(s) would be compatible with the acids and bases involved. (We will ignore any other possible reactions for now.) Your choices of solvents are pentane, diethyl ether, ethanol, water, and ammonia. Refer to Appendix 4 for any needed values of pKa, or estimate them. (a) CH3Li + HCCH CH4 + HCCLi (b) CH3Li + (CH3)3COH CH4 + (CH3)3COLi (c) H N H N CH + 3CH2SH2 + CH3CH2SH + + H H (d) NaNH2 + (CH3)3COH NH3 + (CH3)3CONa (e) (e) HBr + + Br CH3 CH3 C O CH3 H CH3 C +O (f)(f) + HCl + Cl

Write equations for the following acidbase reactions. Label the conjugate acids and bases, and show any inductive stabilization. Predict whether the equilibrium favors the reactants or products. Try to do this without using a table of pKa values, but if you need a hint, you can consult Appendix 4. (a) CH3CH2OH + CH3NH- (b) F3CCOONa + Br3CCOOH (c) CH3OH + H2SO4 (d) NaOH + H2S (e) CH3NH3 + + CH3O- (f) BrCH2CH2OH + F3CCH2O(g) NaOCH2CH3 + Cl2CHCH2OH (h) H2Se + NaNH2 (i) CH3CHFCOOH + FCH2CH2COO- (j) CF3CH2O- + FCH2CH2OH

Rank the following acids in decreasing order of their acid strength. In each case, explain why the previous compound should be a stronger acid than the one that follows it. OH Cl O OH Br O OH Br O OH ClCl O

Like nitrogen and carbon, oxygen also shows this same hybridization effect on acidity. Both of the following compounds can lose a proton from a positively charged oxygen with three bonds to give a conjugate base containing a neutral oxygen with two bonds. One of these structures has pKa = -2.4, while the other has pKa = -8.0. (a) Show the reaction of each compound with water. (b) Match each structure with its pKa, and explain your choice. OC H H H CH3 H H CH3 OCH + +

Consider the type of orbitals involved, and rank the following nitrogen compounds in order of decreasing basicity. Give the structures of their conjugate acids, and estimate their pKas from similar compounds in Appendix 4. Rank the conjugate acids in order of increasing acidity. (Hint: These two orders should be the same!) NCH3 NHCH3 C N

Consider each pair of bases, and explain which one is more basic. Draw their conjugate acids, and show which one is a stronger acid.

Which is a stronger base: ethoxide ion or acetate ion? Give pKb values (without looking them up) to support your choice.

The preceding equation for the protonation of acetamide shows a hypothetical product that is not actually formed. When acetamide is protonated by a strong enough acid, it does not protonate on nitrogen, but at a different basic site. Draw the structure of the actual conjugate acid of acetamide, and explain (resonance) why protonation occurs where it does rather than on nitrogen. Calculate the pKa of this conjugate acid.

Acetic acid can also react as a very weak base (pKb = 20). Two different sites on acetic acid might become protonated to give the conjugate acid. Draw both of these possible conjugate acids, and explain (resonance) why the correct one is more stable. Calculate the pKa of this conjugate acid.

Choose the more acidic member of each pair of isomers, and show why the acid you chose is more acidic.

Choose the more basic member of each pair of isomers, and show why the base you chose is more basic.

In the following acid base reactions, 1. draw Lewis structures of the reactants and the products. 2. determine which species are acting as electrophiles (acids) and which are acting as nucleophiles (bases). 3. use the curved-arrow formalism to show the movement of electron pairs in these reactions, as well as the imaginary movement in the resonance hybrids of the products.

Classify the following hydrocarbons, and draw a Lewis structure for each one. A compound may fit into more than one of the following classifications: alkane cycloalkane aromatic hydrocarbon alkene cycloalkene alkyne cycloalkyne (a) \(\left(\mathrm{CH}_{3} \mathrm{CH}_{2}\right)_{2} \mathrm{CHCH}\left(\mathrm{CH}_{3}\right)_{2}\) (b) \(\mathrm{CH}_{3} \mathrm{CHCHCH}_{2} \mathrm{CH}_{3}\) (c) \(\mathrm{CH}_{3} \mathrm{CCCH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{3}\) (d) (e) (f) (g) (h) (i)

Draw a Lewis structure, and classify each of the following compounds. The possible classifications are as follows: alcohol ketone carboxylic acid ether aldehyde alkene (a) CH2CHCHO (b) CH3CH2CH(OH)CH3 (c) CH3COCH2CH3 (d) CH3CH2OCHCH2 (e) COOH (f) O (g) O (h) CHO (i) CH2OH

Draw a Lewis structure, and classify each of the following compounds: (a) CH3CH2CONHCH3 (b) (CH3CH2)2NH (c) (CH3)2CHCOOCH3 (d) CH3CHCHCOCl (e) (CH3CH2)2O (f) CH3CH2CH2CN (g) (CH3)3CCH2CH2COOH (h) O O (i) O O (j) N CH3 O N CH3 (k) (l) N C O CH3 O O (m) (n) C CH3 O N H COCH3

Circle the functional groups in the following structures. State to which class (or classes) of compounds the structure belongs. (a) CH2CHCH2COOCH3 (b) CH3OCH3 (c) CH3CHO (d) CH3CONH2 (e) CH3NHCH3 (f) RCOOH (g) CH2OH (h) CN (i) O (j) O OH CH2OH OH O hydrocortisone (k) CH3 CH3 C16H33 CH3 CH3 HO O vitamin E

Identify polar and nonpolar molecules. Identify those molecules that engage in hydrogen bonding, either between themselves or with other hydrogen-bond donors. (Problems 2-28, 29, 30, 31, and 32)

Predict general trends in the boiling points and solubilities of compounds based on their size, polarity, and ability to form hydrogen bonds. (Problems 2-31, 32, 33, 34, and 35)

Predict relative acidities and basicities based on the structure, bonding, and resonance of conjugate acid base pairs. (Problems 2-36, 37, 38, 40, 45, 46, 47, 48, and 54)

Calculate and interpret values of \(K_a\), \(K_b\), \(pK_a\), and \(pK_b\). Use these values, and values for similar compounds, to predict products of acid base reactions. (Problems 2-39, 41, 42, 43, 44, and 48)

Identify electrophiles (Lewis acids) and nucleophiles (Lewis bases), and write equations for Lewis acid base reactions using curved arrows to show the flow of electrons. (Problems 2-50, 51, 52, and 53)

Identify alkanes, alkenes, and aromatic hydrocarbons, and draw structural formulas for examples. (Problems 2-55, 56, and 57)

Identify alcohols, ethers, aldehydes, ketones, carboxylic acids, and esters, and draw structural formulas for examples. Problems 2-55, 56, and 57

Identify amines, amides, and nitriles, and draw structural formulas for examples. Problems 2-55, 56, and 57

The CN triple bond in acetonitrile has a dipole moment of about 3.6 D and a bond length of about 1.16 . Calculate the amount of charge separation in this bond. How important is the charge-separated resonance form in the structure of acetonitrile? acetonitrile + CH3 C N CH3 C N

For each of the following compounds, 1. draw the Lewis structure. 2. show how the bond dipole moments (and those of any nonbonding pairs of electrons) contribute to the molecular dipole moment. 3. estimate whether the compound will have a large, small, or zero dipole moment. (a) CH3CHNCH3 (b) CH3CH2OH (c) CBr4 (d) (d) C C CH H3 3 O (e) (e) C C CN CN CN CN (f) (f) N H (g) (g) Cl (h) (h) C C NH H3 2

Sulfur dioxide has a dipole moment of 1.60 D. Carbon dioxide has a dipole moment of zero, even though C - O bonds are more polar than S - O bonds. Explain this apparent contradiction.

Which of the following pure compounds can form hydrogen bonds? Which can form hydrogen bonds with water? Which ones do you expect to be soluble in water? (a) (CH3CH2)2NH (b) (CH3CH2)3N (c) CH3CH2CH2OH (d) (CH3CH2CH2)2O (e) CH3(CH2)3CH3 (f) CH2CHCH2CH3 (g) CH3COCH3 (h) CH3CH2COOH (i) CH3CH2CHO (j) (j) O (k) (k) O O (l) (l) C C H3 NH2

Predict which member of each pair is more soluble in water. Explain your prediction. (a) (a) or O (b) (b) or O O O (c) (c) or O CH3 O (d) (d) or CH2OH (e) (e) or Br Br O (f) (f) or O O

Diethyl ether and butan-1-ol are isomers, and they have similar solubilities in water. Their boiling points are very different, however. Explain why these two compounds have similar solubility properties but dramatically different boiling points. CH3CH2OCH2CH3 CH3CH2CH2CH2OH diethyl ether, bp 35 C butan-1-ol, bp 118 C 8.4 mL dissolves in 100 mL H2O 9.1 mL dissolves in 100 mL H2O

N-Methylpyrrolidine has a boiling point of 81\(^{\circ}\)C, and piperidine has a boiling point of 106\(^{\circ}\)C. (a) Explain the large difference (25\(^{\circ}\)C) in boiling point for these two isomers. (b) Tetrahydropyran has a boiling point of 88\(^{\circ}\)C, and cyclopentanol has a boiling point of 141\(^{\circ}\)C. These two isomers have a boiling point difference of 53\(^{\circ}\)C. Explain why the two oxygen-containing isomers have a much larger boiling point difference than the two amine isomers. (c) N,N -Dimethylformamide has a boiling point of 150\(^{\circ}\)C, and N-methylacetamide has a boiling point of 206\(^{\circ}\)C, for a difference of 56\(^{\circ}\)C. Explain why these two nitrogen-containing isomers have a much larger boiling point difference than the two amine isomers. Also explain why these two amides have higher boiling points than any of the other four compounds shown (two amines, an ether, and an alcohol).

Predict which compound in each pair has the higher boiling point. Explain your prediction. (a) CH3CH2OCH3 or CH3CH(OH)CH3 (b) CH3CH2CH2CH3 or CH3CH2CH2CH2CH3 (c) CH3CH2CH2CH2CH3 or (CH3)2CHCH2CH3 (d) CH3CH2CH2CH2CH3 or CH3CH2CH2CH2CH2Cl (e) (e) or NH CH3 N (f) (f) or O NH CH3 NH

All of the following compounds can react as acids. Without using a table of acidities, rank them in order of increasing acidity. Explain your ranking. (a) \(CH_3CH_2SO_3H\) (b) \(CH_3CH_2OH\) (c) \(CH_3CH_2COOH\) (d) \(CH_3CHClCOOH\) (e) \(ClCH_2CH_2COOH\)

Rank the following species in order of increasing acidity. Explain your reasons for ordering them as you do. HF NH3 H2SO4 CH3OH CH3COOH H3O+ H2O

Rank the following species in order of increasing basicity. Explain your reasons for ordering them as you do. \(\begin{array}{lllllll} \mathrm{NH}_{3} & \mathrm{CH}_{3} \mathrm{O}^{-} & \mathrm{H}_{2} \mathrm{O} & \mathrm{CH}_{3} \mathrm{COO}^{-} & \mathrm{NaOH} & \mathrm{NH}_{2}^{-} & \mathrm{HSO}_{4}^{-} \end{array}\)

The \(K_a\) of phenylacetic acid is \(5.2\ \times\ 10^{-5}\), and the \(pK_a\) of propionic acid is 4.87. (a) Calculate the \(pK_a\) of phenylacetic acid and the \(K_a\) of propionic acid. (b) Which of these is the stronger acid? Calculate how much stronger an acid it is. (c) Predict whether the following equilibrium will favor the reactants or the products.

The following compound can become protonated on any of the three nitrogen atoms. One of these nitrogens is much more basic than the others, however. (a) Draw the important resonance forms of the products of protonation on each of the three nitrogen atoms. (b) Determine which nitrogen atom is the most basic. CH3 NH C NH NH2

The following compounds are listed in increasing order of acidity. In each case, the most acidic proton is shown in red. (a) Show the structure of the conjugate base of each acid, including any resonance forms. (b) Explain why X is a stronger acid than W. (c) Explain why Y is a stronger acid than X. (d) Explain why Z is a stronger acid than Y.

Predict the products of the following acid–base reactions. (a) \(\mathrm{H}_{2} \mathrm{SO}_{4}+\mathrm{CH}_{3} \mathrm{COO}^{-} \rightleftarrows\) (b) \(\mathrm{CH}_{3} \mathrm{COOH}+\left(\mathrm{CH}_{3}\right)_{3} \mathrm{~N}: \rightleftarrows\) (e) \(\mathrm{H}_{2} \mathrm{O}+\mathrm{NH}_{3} \longleftrightarrow\) (g) \(\mathrm{HCOOH}+\mathrm{CH}_{3} \mathrm{O}^{-} \longleftrightarrow\)

Consider the following proposed Brønsted–Lowry acid–base reactions. In each case, draw the products of a transfer of the most acidic proton on the acid to the most basic site on the base. Use Appendix 4 to find or estimate the \(pK_a\) values for the acids and the \(pK_b\) values for the bases. Then determine which side of the reaction is favored, either reactants or products.

Compare the relative acidity of 1-molar aqueous solutions of the following acids. \(\begin{array}{lllllll} \mathrm{NH}_{4} \mathrm{Cl} & \mathrm{CH}_{3} \mathrm{COOH} & \mathrm{BrCH}_{2} \mathrm{COOH} & \mathrm{F}_{3} \mathrm{CCOOH} & \mathrm{H}_{2} \mathrm{SO}_{4} & \mathrm{HCl} & \mathrm{HBr} \end{array}\) \(\mathrm{p} K_{\mathrm{a}}=9.26\ \ \ \quad \mathrm{p} K_{\mathrm{a}}=4.74\ \ \ \quad \mathrm{p} K_{\mathrm{a}}=2.9\ \ \ \quad \mathrm{p} K_{\mathrm{a}}=0.2\ \ \ \quad \mathrm{p} K_{\mathrm{a}}=-5\ \ \ \quad \mathrm{p} K_{\mathrm{a}}=-7\ \ \ \quad \mathrm{p} K_{\mathrm{a}}=-9\)

The following compounds can all react as acids. (a) For each compound, show its conjugate base. Show any resonance forms if applicable. (b) Rank the conjugate bases in the order you would predict, from most stable to least stable. (c) Rank the original compounds in order, from strongest acid to weakest acid.

The following compounds can all react as bases. (a) For each compound, show its conjugate acid. Show any resonance forms if applicable. (b) Rank the conjugate acids in the order you would predict, from most stable to least stable. (c) Rank the original compounds in order, from strongest base to weakest base.

The following compounds can all react as acids. (a) For each compound, show its conjugate base. Show any resonance forms if applicable. (b) Rank the conjugate bases in the order you would predict, from most stable to least stable. (c) Rank the original compounds in order, from strongest acid to weakest acid.

Consider the following compounds that vary from nearly nonacidic to strongly acidic. Draw the conjugate bases of these compounds, and explain why the acidity increases so dramatically with substitution by nitro groups. \(\begin{array}{llll} \mathrm{CH}_{4} & \mathrm{CH}_{3} \mathrm{NO}_{2} & \mathrm{CH}_{2}\left(\mathrm{NO}_{2}\right)_{2} & \mathrm{CH}\left(\mathrm{NO}_{2}\right)_{3} \end{array}\) \(\mathrm{p} K_{\mathrm{a}} \cong 50\ \ \ \quad \mathrm{p} K_{\mathrm{a}}=10.2\ \ \ \quad \mathrm{p} K_{\mathrm{a}}=3.6\ \ \ \quad \mathrm{p} K_{\mathrm{a}}=0.17\)

Methyllithium (CH3Li) is often used as a base in organic reactions. (a) Predict the products of the following acidbase reaction. CH3CH2OH + CH3Li (b) What is the conjugate acid of CH3Li? Would you expect CH3Li to be a strong base or a weak base?

Label the reactants in these acid–base reactions as Lewis acids (electrophiles) or Lewis bases (nucleophiles). Use curved arrows to show the movement of electron pairs in the reactions.

In each reaction, label the reactants as Lewis acids (electrophiles) or Lewis bases (nucleophiles). Use curved arrows to show the movement of electron pairs in the reactions. Draw any nonbonding electrons to show how they participate in the reactions.

Each of these compounds can react as an electrophile. In each case, use curved arrows to show how the electrophile would react with the strong nucleophile sodium ethoxide, \(\mathrm{Na}^{+-} \mathrm{OCH}_{2} \mathrm{CH}_{3}\). (b) NH_4^+ (c) \(CH_3CH_2Br\) (d) \(BH_3\) (e) \(CH_3COOH\) (f) \(H_2C=CH-CHO\)

Each of these compounds can react as a nucleophile. In each case, use curved arrows to show how the nucleophile would react with the strong electrophile BF3. (a) (a) O (b) (b) (c) (c) O (d) (CH3)3N (e) CH3CH2OH (f) (CH3)2S

The pKa of ascorbic acid (vitamin C, page 55) is 4.17, showing that it is slightly more acidic than acetic acid (CH3COOH, pKa 4.74). (a) Show the four different conjugate bases that would be formed by deprotonation of the four different OH groups in ascorbic acid. (b) Compare the stabilities of these four conjugate bases, and predict which OH group of ascorbic acid is the most acidic. (c) Compare the most stable conjugate base of ascorbic acid with the conjugate base of acetic acid, and suggest why these two compounds have similar acidities, even though ascorbic acid lacks the carboxylic acid (COOH)group.

Give a definition and an example for each class of organic compounds. (a) alkane (b) alkene (c) alkyne (d) alcohol (e) ether (f) ketone (g) aldehyde (h) aromatic hydrocarbon (i) carboxylic acid (j) ester (k) amine (l) amide

Circle the functional groups in the following structures. State to which class (or classes) of compounds the structure belongs. (a) (a) O O (b) (b) COOH (c) (c) CHO (d) (d) O (e) (e) O O (f) (f) O N H (g) (g) CH2OCH3 CN (h) (h) CH3 C COOCH3 NH2 H (i) (i) H2N CH COOH CH2 OH

Many naturally occurring compounds contain more than one functional group. Identify the functional groups in the following compounds: (a) Penicillin G is a naturally occurring antibiotic. (b) Dopamine is the neurotransmitter that is deficient in Parkinsons disease. (c) Capsaicin gives the fiery taste to chili peppers. (d) Thyroxine is the principal thyroid hormone. (e) Testosterone is a male sex hormone. HO CH2C HO CH3O HO HO O I I CH2 I I H2 NH2 CH COOH NH2 C O NH N S COOH penicillin G O dopamine capsaicin thyroxine O OH testosterone