INTRO ORGANIC ANSWERS
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INTRO ORGANIC ANSWERS
a) ketone
b) alkyne
c) alcohol
d) aldehyde
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INTRO ORGANIC ANSWERS
2.
3.
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INTRO ORGANIC ANSWERS
a)
b)
c)
d)
e)
f)
g)
h)
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INTRO ORGANIC ANSWERS
4.
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INTRO ORGANIC ANSWERS
a)
b)
d)
e)
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INTRO ORGANIC ANSWERS
5.
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INTRO ORGANIC ANSWERS
a)
c)
d)
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INTRO ORGANIC ANSWERS
6. Synthetic organic compounds include medicines, dyes, paints, polymers, pesticides, food additives, fibers, etc.
7. Natural organic compounds include hair, skin, muscles, vegetables, meats, coal, oil, natural gas, etc.
8. < 10 % is for chemical products and > 90% are burned as energy.
9. Carbon has 4 bonds in all of its compounds. It can never exceed 4 bonds, because only the 2s and 2p orbitals are available and they can hold a maximum of 8 valence electrons (4 bonds). The 3s orbital is too high in energy to be used by carbon. Carbon has 3 bonds in some of its C+ intermediates formed during reactions but these are not stable products. Intermediates are short-lived, reactive species.
10. valence
11. Isoelectronic means ‘having the same electronic configuration’.
12.
13. Group number = number of valence electrons, for the representative (Group A) elements.
14. Valence electrons are those in the highest shell. They do not include inner shell electrons.
16.
17.
18.
a)
b)
c)
d)
20. Electronegativity is a number indicating how strongly an atom attracts electrons to which it is bonded. Non metals have high EN, e.g., F = 4.0 and metals have low EN, e.g., Na = 1.0
21. The periodic trends in EN in each cluster below are shown. 1 = lowest, 3 = highest.
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INTRO ORGANIC ANSWERS
a) F Cl Br EN decreases down each Group as size of the atoms increase
b) N O F EN increases left to right across each period as the net core charge increases
c) Li Na K EN decreases down each group
d) Be B C EN increases left to right across each period
22. 0.0, Choose pairs of non metals, since non metals can form covalent bonds, (CS2, PH3, CI4)
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INTRO ORGANIC ANSWERS
a) non polar covalent: 0.0 £ DEN £ 0.4, e.g., CH4, DEN(C-H) = (2.5-2.1) = 0.4
b) polar covalent: 0.5 £ DEN £ 1.7, e.g., HCl, DEN(Cl-H) = (3.0 –2.1) = 0.9
c) ionic 1.8 £ DEN £ 3.2, e.g., NaF, DEN(F-Na) = (4.0 – 1.0) = 3.0
24. d+, d-
25. Separation of + and – charge is called an (electric) ‘dipole’.
26. The movement of electron density through sigma (s) bonds is called the inductive effect. In a s bond, electrons spend most of their time nearer the more electronegative element, the bond is ‘polarized’. For example, in an OH bond, the electrons spend most of their time nearer O than H, since O is more electronegative.
a) DEN in NaBr = 1.8 and the compound has ionic bonds
b) DEN in BeBr2 = 1.3 and the compound has polar covalent bonds.
c) DEN in NCl3 = 0.0 and the compound has pure covalent bonds.
28. He 1s2, Ne 2s22p6, Ar 3s23p6, Kr 4s24p6, Xe 5s25p6, Rn 6s26p6. Noble gases are stable (chemically unreactive). Other representative elements react to gain, lose or share electrons to become isoelectronic with the nearest noble gas.
29. Lowest IE = 1, highest IE = 4. Atoms with the highest electronegativity have the highest IE also.
a) transition metals, non metals, alkali metals, metalloids
2 4 1 3
30. Valence Shell Electron Pair Repulsion Theory (VSEPR).
31. Carbon (Group 4A) 6C 1s2 2s22px12py12pz0
32. A single bond is also called a sigma (s) bond.
a) A double bond is made of 1 s bond and 1 p bond.
b) A triple bond is made of 1 s bond and 2 p bonds
33. The hybridization state of carbon in the following situations is given:
a) C has four s bonds = sp3 hybridization
b) C has three s bonds and one p bond = sp2 hybridization
c) C has two s bonds and two p bonds = sp hybridization
34. The hybridization state of atoms are shown in the following table:
C
/ N / O / H / Halogenonly s bonds (no p bonds) / sp3 / sp3 / sp3 / unhybridized / unhybridized
one p bond (1double bond) / sp2 / sp2 / sp2 / does not form / ------
two p bonds (2 double or 1 triple) / sp / sp / does not form / does not form / ------
35.
36. Hydrogen is unhybridized in all of its compounds.
37. Other than a few exceptions that we will study later, singly bonded halogens are always unhybridized.
a) The C in a methyl cation is sp2 hybridized.
b) The C in a methyl radical is also sp2 hybridized.
c) The C in a methyl anion is sp3 hybridized
39. conjugated, isolated, cumulated.
40.
41. The carbocation stability order of 3° > 2° > 1° > methyl is the result of two interactions, the inductive effect and hyperconjugation. Re: the inductive effect: Alkyl groups are weak electron donor groups. They donate electron density to the C+ through s bonds. This delocalizes (spreads out) the + charge on the C+ rendering the C+ less reactive (more stable). 3° C+’s have the most (three) alkyl groups directly bonded the C+ whereas methyl C+’s have the least (none). H atoms are not electron donating. Re: hyperconjugation: The C+ is stabilized by a shift of electron density from adjoining alkyl groups via partial overlap between the C+’s empty p orbital and the s bonds (e.g., C-H bonds) in the alkyl groups. See page 19 in the ORGANIC INTRO NOTES for pictures.
42. Inductive effect and Hyperconjugation.
43.
44.
45.
46.
47. Be, B and Al
48. Hypervalent atoms have expanded valence shells, i.e., they have more than 8 around them in their bonded structures. They can use not only their ns and np orbitals but also their nd orbitals.
Other examples are possible.
49.
50. Resonance delocalizes electric charge. Delocalization (spreading out) charge reduces the reactivity of the charged atom.
51. Arrhenius acid. An Arrhenius base is one that contains the OH group and produces OH- in water. Examples include hydroxides of active metals, e.g., NaOH, KOH, LiOH, Ca(OH)2, etc.
52. A Bronsted acid is a proton (H+) donor, e.g., HCl. A Bronsted base is a proton acceptor, e.g., NH3, NH2-, CH3O-, CH3COO-, etc.
53. ‘conjugate’ acid/base pairs.
Bronsted acid / pKa / Bronsted base / pKbCH3COOH / 4.7 / CH3COO- / 9.3
H2O / 15.74 / OH- / -1.74
H3BO3 / 9.2 / H2BO3- / 4.8
HAsO4-2 / 11.5 / AsO4-3 / 3.5
HCO3- / 10.3 / CO3-2 / 3.7
HNO2 / 3.1 / NO2- / 10.9
HSO4- / 2.0 / SO4-2 / 12.0
55. H3O+, hydronium ion, pKa = -1.74. OH-, hydroxide ion, pKb = -1.74
56. Water reacts with acids stronger than the hydronium ion, producing hydronium ion. The strength of strong acids is reduced (leveled) to pKa = -1.74 . Water reacts with bases stronger than hydroxide ion producing hydroxide ion. The strength of strong bases is reduced (leveled) to pKb = -1.74.
57.
% / pKeq / Acid / Base / Conj. Base / Conj. Acid100 / -14.4 / HBr / NaHCO3 / ® / NaBr / H2CO3
15 / +1.5 / HN3 / KF / ® / KN3 /
HF
97 / -3.3 / H2SO4 / H2O / ® / HSO4- / H3O+58. pKeq £ -3 and Keq ³ 1000
a) False
b) True
60. A Lewis acid is an electron pair acceptor, e.g., AlCl3, a carbocation such as CH3+ and others (see notes pages 34 & 35).
61. A Lewis base is an electron pair donor, e.g., Li+H:-, F- and others (see notes pages 34 & 35).
62. Binary acids increase in strength left-to-right across each period and down each group. Electrophile strength is the same. A good H+ donor is also a good electron pair acceptor.
Conjugate bases of binary acids increase in strength right-to-left across each period (and so does nucleophilic strength). In general, a stronger base is a better nucleophile. However conjugate bases of binary acids increase in strength up each group but nucleophilic strength increases down each group as the nucleophile grows larger. Increasing size contributes more to nucleophile strength. The larger nucleophiles are said to be more ‘polarizable’ as they can distort their outer valence electron cloud to readily make bonds by donating electrons. The valence electrons of these larger nucleophiles are farther from and more loosely held by the distant nucleus.
63. OH-, H-, NH2-, etc. are strong Bronsted bases (see pK table) and good nucleophiles (see nucleophilicity table, p.39).
Br-, I-, CN-, etc. are weak Bronsted bases and good nucleophiles.
H3O+, HCl, H2SO4, BF3, etc. are strong Bronsted acids and good electrophiles.
64.
65. Without looking in pK tables, in each group, number each compound in order of increasing acidity, where 1 = least acidic and 4 = most acidic.
a) HBr HF HCl HI
b) OH2 NH3 HF CH4
c) CHF2COOH CH2FCOOH CH3COOH CF3COOH
66. For polyprotic acids, their pKa increases (acidity decreases) by a factor of ca. 105 for each H removed.
a) the acidity of H2SO3 is approximately 105 ´ greater than its conjugate base HSO3-
b) the acidity of H3AsO4 is approximately 1010 ´ greater than HAsO4-2
67. For oxyacids of the same central atom but differing number of oxygens such as shown below, pKa decreases (acidity increases) by a factor of ca. 105 for each oxygen added. The additional oxygens produce more resonance structures to stabilize the conjugate base formed after the acid donates a proton. Since the conjugate base is weaker, the related acid must be stronger.
HIO, HIO2, HIO3, HIO4
acidity increasing
68. The most polarizable groups have the least electronegative central atom and are the largest (valence electrons farthest from the nucleus).
a) H2O H2S H2Se
b) NH3 PH3 AsH3
c) F- Cl- Br- I-
69. The best leaving group is the most polarizable and is the most stable base (if it leaves as an anion) or neutral (if one must choose between an anion or a neutral species). It takes more energy to separate oppositely charged ions than neutral species.
a) -I -Br -Cl -F
b) -OH2+ -OH
c) -NH3+ -NH2
70. Nucleophiles can be negative or neutral but never positive; they can be basic, neutral or weakly acidic but never strongly acidic. Electrophiles can be positive or neutral but never negative; they can be acidic, neutral or even weakly basic, but not strongly basic.
a) cannot be a nucleophile SO4-2 HSO4- H2SO4 Fe+3
b) cannot be an electrophile H+ OH- CH3OH H2O
71. Mechanisms show the movement of electrons, which is always from nucleophile to electrophile, i.e., Nu:- ® E+. Mechanisms do not show movement of atoms, ions or molecules. We know that molecules must collide in order to react but it does not matter which species strikes another or which way they are moving.
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