The C=N triple bond in acetonitrile has a dipole moment of about 3.6 D and a bond length of about 1.16 Å. Calculate the amount of charge separation in this bond. How important is the charge-separated resonance form in the structure of acetonitrile? |CH,-C=N: → CH,-ċ=N 道, acetonitrile

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Chapter1: Chemical Foundations
Section: Chapter Questions
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The C=N triple bond in acetonitrile has a dipole moment of about 3.6 D and a bond length of about 1.16 Å. Calculate the
amount of charge separation in this bond. How important is the charge-separated resonance form in the structure of acetonitrile?
2-28
CH,-C=N: → CH,-ċ=N:
acetonitrile
For each of the following compounds,
1. draw the Lewis structure.
2-29
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.
(а) CН
CH=N-CH3
() CH; — СН,ОН
(c) СВr
NC.
CN
(d)
CH, —С—СH,
(e)
(f)
NC
CN
H
.Cl
(8)
(h)
CH, —С—NH,
2-30
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.
2
CHAPTER 2
Acids and Bases; Functional Groups
2-31
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
(d) (CH;CH,CH2),O
(b) (CH3CH2)3N
(c) CH;CH-CH,ОН
(e) CH3(CH,);CH3
(f) CH2=CH-CH,CH3
(g) CH3COCH3
(h) CH-CH-COОН
() CH;СH-CHО
(k)
(1)
CH, —С—NH,
2-32
Predict which member of each pair is more soluble in water. Explain your prediction.
-CH,
(a)
or
(b)
or
(c)
or
Br
(d)
-CH,OH
(e)
(f)
or
or
Br
or
Transcribed Image Text:The C=N triple bond in acetonitrile has a dipole moment of about 3.6 D and a bond length of about 1.16 Å. Calculate the amount of charge separation in this bond. How important is the charge-separated resonance form in the structure of acetonitrile? 2-28 CH,-C=N: → CH,-ċ=N: acetonitrile For each of the following compounds, 1. draw the Lewis structure. 2-29 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. (а) CН CH=N-CH3 () CH; — СН,ОН (c) СВr NC. CN (d) CH, —С—СH, (e) (f) NC CN H .Cl (8) (h) CH, —С—NH, 2-30 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. 2 CHAPTER 2 Acids and Bases; Functional Groups 2-31 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 (d) (CH;CH,CH2),O (b) (CH3CH2)3N (c) CH;CH-CH,ОН (e) CH3(CH,);CH3 (f) CH2=CH-CH,CH3 (g) CH3COCH3 (h) CH-CH-COОН () CH;СH-CHО (k) (1) CH, —С—NH, 2-32 Predict which member of each pair is more soluble in water. Explain your prediction. -CH, (a) or (b) or (c) or Br (d) -CH,OH (e) (f) or or Br or
2-37
Rank the following species in order of increasing acidity. Explain your reasons for ordering them as you do.
HF NH3 H,SO4 CH3OH CH;COOH H,O* H,0
2-38
Rank the following species in order of increasing basicity. Explain your reasons for ordering them as you do.
NH3 CH30
H2O CH3CO0"
NaOH
NH,
HSO,
2-39
The Ka of phenylacetic acid is 5.2 × 10°, and the pK, of propionic acid is 4.87.
CH, —С—оН
CH, —СH, —С-ОН
phenylacetic acid, K = 5.2 x 10-s
propionic acid, pK, = 4.87
(a) Calculate the pKa of phenylacetic acid and the Ka 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.
CH,COO
+ CH,CH,COOH
-CH,COOH + CH,CH,COO-
*2-40
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.
NH
CH, —NH—С
`NH,
2-41
The following compounds are listed in increasing order of acidity. In each case, the most acidic proton is shown in red.
OH
CH,
NH
H
H.
W, pKa = 25
X, pKa = 23
Y, pKa = 8.8
Z, pKa = 4.2
(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.
(а) H-SO4
2-42
CH;COO
(b) СH;CООН
(CH3)3N:
(c)
С—ОН
+
FHO-
(d) Но—С— ОН
+ 2-ОН
(1) (CH.),NH
(h) NH,CH,COOH +
(е) Н,О
+
NH,
OH
(g) HCООН
CH30
2 -ОН
2-43
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 pKa values for the
acids and the pKp values for the bases. Then determine which side of the reaction is favored, either reactants or products.
СООН
(а)
(b)
O,N
O,N
Transcribed Image Text:2-37 Rank the following species in order of increasing acidity. Explain your reasons for ordering them as you do. HF NH3 H,SO4 CH3OH CH;COOH H,O* H,0 2-38 Rank the following species in order of increasing basicity. Explain your reasons for ordering them as you do. NH3 CH30 H2O CH3CO0" NaOH NH, HSO, 2-39 The Ka of phenylacetic acid is 5.2 × 10°, and the pK, of propionic acid is 4.87. CH, —С—оН CH, —СH, —С-ОН phenylacetic acid, K = 5.2 x 10-s propionic acid, pK, = 4.87 (a) Calculate the pKa of phenylacetic acid and the Ka 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. CH,COO + CH,CH,COOH -CH,COOH + CH,CH,COO- *2-40 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. NH CH, —NH—С `NH, 2-41 The following compounds are listed in increasing order of acidity. In each case, the most acidic proton is shown in red. OH CH, NH H H. W, pKa = 25 X, pKa = 23 Y, pKa = 8.8 Z, pKa = 4.2 (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. (а) H-SO4 2-42 CH;COO (b) СH;CООН (CH3)3N: (c) С—ОН + FHO- (d) Но—С— ОН + 2-ОН (1) (CH.),NH (h) NH,CH,COOH + (е) Н,О + NH, OH (g) HCООН CH30 2 -ОН 2-43 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 pKa values for the acids and the pKp values for the bases. Then determine which side of the reaction is favored, either reactants or products. СООН (а) (b) O,N O,N
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