Excerpts for McGraw-Hill's 500 Organic Chemistry Questions : Ace Your College Exams


McGraw-Hill's 500 Organic Chemistry Questions

Ace Your College Exams
By Estelle Meislich Herbert Meislich Jacob Sharefkin

McGraw-Hill

Copyright © 2013 The McGraw-Hill Companies, Inc.
All right reserved.

ISBN: 978-0-07-178965-3

Contents



Chapter One

Structure and Properties

1. What are the important differences between organic and inorganic compounds?

2. What are the three important classes of organic compounds?

3. Specify the type of chemical bond in the following compounds:

(A) Li2O

(B) PH3

(C) N2O

(D) CaF2

4. How does the Lewis—Langmuir octet rule explain the formation of chemical bonds?

5. Identify donor and acceptor species in the formation of coordinate covalent bonds in the following:

(A) H3O+

(B) Cu(NH3)2+4

(D) H3N : BF3

6. Write electron-dot structures for the following covalent compounds:

(A) F2O

(B) H2O2

(C) PCl3

(D) CH3Cl

(E) N2H4 (hydrazine)

7. Determine the positive or negative charge, if any, on the following:

(A) [ILLUSTRATION OMITTED]

(B) [ILLUSTRATION OMITTED]

(C) [ILLUSTRATION OMITTED]

(D) [ILLUSTRATION OMITTED]

(E) [ILLUSTRATION OMITTED]

8. Write structural formulas for the following:

(A) HOCl

(B) CH3Br

(C) HONO

(D) ClCN

9. Write two isomeric structures with the molecular formula C2H6O.

10. Derive all structural formulas for the isomers of the following:

(A) C3H8

(B) C4H10.

(C) C5H12

11. Write structural formulas for all the C4H8 isomers.

12. Give structural formulas for cyclic compounds having the molecular formula C5H10.

13. Determine the formal charges on each atom in the following:

(A) H:O:Cl

(B) NH+

(C) H2O:BF3

14. Write Lewis structures with FCs for the following:

(A) Nitric acid, HONO2

(B) Sulfuric acid, HOSO2OH

15. With the aid of formal charges, determine which Lewis structure is more likely to be correct for each of the following molecules:

(A) [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]

(B) [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]

16. (A) Define a functional group.

(B) Why are functional groups important in organic chemistry?

17. (A) Write the structure for a 3-C carboxylic acid.

(B) Show structures for the following derivatives of this acid:

I. an ester

II. an acid chloride

III. an amide

18. Analysis of a compound A gives 92.25% C and 7.743% H. Calculate the following:

(A) its empirical formula

(B) its molecular formula

The molecular weight (MW) is determined to be 78.11g/mol.

19. An 11.75-g sample of a hydrocarbon is volatilized at 1-atm pressure and 100°C to a gas that occupies 5.0 L. What is its MW? (R = 0.0821 L · atm/mol · K)

20. Complete combustion of 0.858 g of compound X gives 2.63 g of CO2 and 1.28 g of H2O.

(A) Find the % composition of X.

(B) What is the lowest MW it can have?

21. The molal freezing point depression constant for camphor as a solvent is 40°C kg/mol. Pure camphor melts at 179°C. When 0.108 g of compound A is dissolved in 0.90 g of camphor, the solution melts at 166°C. Find the molecular weight of A.

22. In a nitration of benzene, 10.0 g of benzene gave 13.2 g of nitrobenzene.

(A) What is the theoretical yield of nitrobenzene?

(B) What is the percentage yield?

Chapter Two

Bonding and Molecular Structure

23. Give the relationship between the principal energy level (shell), n, and

(A) the maximum number of e-s in a shell

(B) the number of sublevels (subshells) in a shell

(C) For the third shell (n = 3), give

I. the maximum number of electrons

II. the number of subshells

24. (A) Give the shape and draw the cross section of the following:

I. a 1s AO

II. a 2p AO

(B) How are these shapes determined?

(C) State whether an electron can ever be in the nucleus of an atom with

I. an s AO

II. a p AO

(D) Respond to the question, "How can an e- move from one lobe of a p AO to the other lobe without passing through the nucleus?"

25. (A) State the Aufbau (German for "building up") principle for filling orbitals with electrons.

(B) State and explain Hund's rule for filling orbitals.

(C) Give the electron distribution for a ground state C atom that

I. follows Hund's rule

II. does not follow Hund's rule

(D) If individual C atoms could be isolated (they cannot be), what different physical properties would separate the two electron distributions given in (C)?

(E) Which are the valence electrons?

26. Draw an energy diagram showing the relationship between two AOs and the MOs resulting from their combination.

27. Sketch the combination of the needed AOs to form the following MOs:

(A) σs (sigma)

(B) σsp

(C) πy (pi)

28. Sketch the formation of the following MOs:

(A) σ*s

(B) σ*sp

(C) π*y

29. (A) How are electrons distributed in the MOs when two atoms interact to form a bond?

(B) Illustrate (A) with H+2, H2, HHe, and He2. Give the symbolism for the molecular orbital electronic structure.

(C) How can a MO electronic structure be used to predict whether these (or any species) can exist?

(D) Which, if any, do not exist?

(E) List each substance in decreasing order of stability.

30. (A) Define the term bond order.

(B) Give the bond order of C2, N2, O2, NO, CN-.

31. (A) Account for the observed bond angles of

I. 107° in NH3

II. 105° in H2O

(B) Could N and O use ground state AOs to form equivalent bonds?

(C) Why do N and O use HOs for bonding?

32. (A) Give the HO used by N and C.

(B) Predict its shape for each of the following:

I. NH+4

II. CH3NH2

III. H2C = O

IV. H2C = NH

V. HC = N

33. What kinds of hybrid orbitals are predicted for the underlined atom?

(A) H2NOH

(B) H2S

(C) [B.bar]F-4

(D) HO[C.bar] [equivalent to] [N.bar]

(E) O = [C.bar] = O

(F) H2[C.bar] = [C.bar] = O

34. (A) Arrange the gaseous hydrogen halides in order of decreasing dipole moments and rationalize your order.

(B) The dipole moments for the methyl halides are: CH3F, 1.82 D; CH3Cl, 1.94 D; CH3Br, 1.79 D; and CH3I, 1.64 D. Explain.

35. Organometallics are compounds containing C—metal bonds. Metals typically have low electronegativity values, and the C—metal bond moment is toward the more electronegative C.

(A) What generalization can be made as to the nature of the C—metal bond and the electronegativity of the metal?

(B) State the kind of bond you would expect between C and

I. an alkali metal

II. a group 2 metal

Give an example of each.

(C) Give an example of a C—metal bond that contains little or no ionic character. (Refer to a table of electronegativity values, if necessary.)

36. The usual ONs of the following atoms are given: for H, +1; for O, —2; and for halogens (X), —1. Determine the ON of the underlined atom in each species:

(A) [C.bar]O2

(B) [P.bar]Cl3

(C) [N.bar]2O5

(D) [S.bar]O2-3

(E) [N.bar]H+4

37. (A) How does the oxidation number reveal whether a substance has undergone oxidation or reduction?

(B) Identify the following changes as oxidations, reductions, or neither.

I. CH4 -> CH3OH

II. H2CCl2 -> H2 C=O

III. H2C = CH2 -> H3CCH3

IV. [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]

38. Define the three types of intermolecular forces that can lead to interactions between neutral molecules, in order of decreasing strength.

39. The boiling point of H2O (100°C) is much higher than that of HF (-83°C), even though they both form H bonds and have similar molecular weights. Explain.

40. The three isomeric pentanes, C5H12, have boiling points of 9.5, 28, and 36°C. Match each boiling point with the correct structure and give your reasons.

41. (A) Differentiate between structural isomers and contributing (resonance) structures.

(B) What is a resonance hybrid?

42. Write resonance structures for the following substances, showing all outer- shell electrons and formal charges when present:

(A) formate ion, HCO-2

(B) nitrite ion, NO-2

(C) formaldehyde, H2CO

(D) nitrate ion, NO-3

43. (A) Describe the resonance hybrid of

I. NO-2

I. NO-3

in terms of overlapping atomic orbitals.

(B) What is meant by the term delocalization (resonance) energy?

(C) Compare the delocalization (resonance) energies (stabilities) of NO-2 and NO-3.

44. Explain why each of the following structures is not a resonance form.

(A) :[??]=[??]: and :[??]-[??]:

(B) H2[??]-O-H and H2[??]=0-H

(C) [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]

Chapter Three

Chemical Reactivity and Organic Reactions

45. Classify each of the following carbon intermediates:

(A) C2H5[??]—H

(B) (CH3)3

(C) CH3[??]HCH3

(D) H2C = CH - CH+2

46. Supply the structure and type for the intermediate species designated by:

(A) [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]

(B) [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]

(C) [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]

(D) CH3CHI2 + Zn -> ? ZnI2

(E) CH3CH2Cl + AlCl3 ->? + [AlCl4]-

(F) [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]

(G) [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]

47. (A) What is the major factor that influences the relative stabilities of carbanions, radicals, and carbocations?

(B) Define the term inductive effect.

(C) How does the inductive effect of alkyl group affect the stability of these three intermediates?

48. Give the type of each of the following reactions. (A reaction may belong to more than one type.)

(A) H2C=CH2+Br2 -> H2CBr—CH2Br

(B) HO:- + CH3Cl -> CH3OH + Cl-

(C) Me2NH+2 + CH3O- -> Me2NH+CH3OH

(D) CHCl3 + OH- ->: CCl2 + H2O+Cl-

(E) [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]

(F) [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]

(G) [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]

(H) [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]

(I) [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]

(J) [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]

(K) [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]

49. The following equation represents the mechanistic steps for chlorination of methane:

[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]

(A) Write the equation for the overall reaction obtained from the sum of the propagation steps 2 and 3, and give its classification.

(B) List the intermediates in all the steps.

(C) Which steps are homolytic?

(D) Classify step 1.

(E) List the displacement steps.

(F) Are any of the steps additions?

(G) Which step follows step 3?

(H) Name the reactions whose steps keep repeating themselves.

(I) Write an equation for the formation of a by-product from the collision of intermediates. Classify this reaction.

50. Identify the species I and II as electrophiles (E) or nucleophiles (Nu) in the following reactions:

[TABLE OMITTED]

51. (A) Identify the acids and bases and the conjugate acid-base pairs when

I. CH3COOH

II. CH3NH2 dissociate in water.

(B) What generalization can be made about the net direction of the acid-base equilibrium?

(C) Draw a conclusion about the acid-base behavior of H2O.

52. Identify reactants I and II as a Lewis acid A or Lewis base B in the following:

[TABLE OMITTED]

53. Discuss how

(A) acid strength is related to Ka, the acid ionization constant, and to pKa

(B) base strength is related to Kb, the base ionization constant, and to pKb

The values of pKa and pKb are defined as —log Ka and —log Kb, respectively.

54. Account for the greater acidity of acetic acid, CH3COOH (abbreviated HOAc), in water than in methanol, MeOH.

55. Compare the following:

(A) the acid strengths of CH3COOH, ClCH2COOH, Cl2CHCOOH, and Cl3CCOOH

(B) the base strengths of their conjugate bases

56. Account for the fact that, unlike other amines (RNH2), guanidine, is a strong base.

57. (A) Which thermodynamic function is most often used in organic chemistry to express the heat of a reaction?

(B) Give the sign of [increment of H] for an

I. exothermic

II. endothermic reaction

(C) Give the algebraic sign of [increment of H] for a reaction involving

I. breaking

II. formation of covalent bonds

(D) Give the symbol used for change in enthalpy for reactions whose participating compounds are in their standard state.

58. (A) Define bond-dissociation energy.

(B) Find the algebraic sign of the [increment of H] values used for

I. bond-dissociation energies, [increment of H]d

II. bond formation

(C) What is the difference between bond-dissociation energy and bond energy?

(D) Which value is found in most tables?

(E) How are bond strengths and [increment of H] values related?

59. (A) Use the bond-dissociation energy values, given in kcal/mol in parentheses, to calculate the heat of reaction, [increment of H]r, for monobromination of methane:

H3C - H(102) + Br - Br(46)->H3C - Br(70) + H - Br(88)

(B) Is this reaction endothermic or exothermic?

60. Find [increment of H]r for the following reaction, and decide whether it is exothermic or endothermic. The values in parentheses are, as usual, in kJ/mol.

H2C - CH2(590) + H - H(435)->H3C - CH3(for C - C, 368; for C - H, 410)

61. (A) Define standard heat of formation, [increment of Hf

(B) Write the equation for the [increment of Hf formation of acetylene, C2H2.

(C) Calculate [increment of Hf for C2H2 from the following thermochemical combustion equations (complete oxidations with O2), where (g) and (l) are for gas and liquid, respectively.

I. [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]

II. [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]

III. [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]

Note that fractional numbers of moles of O2 are used in these equations in order to have 1 mol of the compound oxidized. This is done because the [increment of H]°'s are given per mole of reactant oxidized.

(D) What can be said about the chemical stability of acetylene?

62. Calculate [increment of G]° for monochlorination of methane (Ke = 4.8×1018 at standard conditions and 25°C).

63. From the signs of [increment of H] and T]increment of S] tabulated below for reactions (A)-(D) predict the sign of [increment of G], the direction in which the reaction proceeds, and whether Ke is more or less than 1.

(Continues...)



Excerpted from McGraw-Hill's 500 Organic Chemistry Questions by Estelle Meislich Herbert Meislich Jacob Sharefkin Copyright © 2013 by The McGraw-Hill Companies, Inc.. Excerpted by permission of McGraw-Hill. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
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